=
=
"""Break *iterable* into lists of length *n*:
>>> list(chunked([1, 2, 3, 4, 5, 6], 3))
[[1, 2, 3], [4, 5, 6]]
By the default, the last yielded list will have fewer than *n* elements
if the length of *iterable* is not divisible by *n*:
>>> list(chunked([1, 2, 3, 4, 5, 6, 7, 8], 3))
[[1, 2, 3], [4, 5, 6], [7, 8]]
To use a fill-in value instead, see the :func:`grouper` recipe.
If the length of *iterable* is not divisible by *n* and *strict* is
``True``, then ``ValueError`` will be raised before the last
list is yielded.
"""
=
yield
return
return
"""Return the first item of *iterable*, or *default* if *iterable* is
empty.
>>> first([0, 1, 2, 3])
0
>>> first([], 'some default')
'some default'
If *default* is not provided and there are no items in the iterable,
raise ``ValueError``.
:func:`first` is useful when you have a generator of expensive-to-retrieve
values and want any arbitrary one. It is marginally shorter than
``next(iter(iterable), default)``.
"""
return
return
"""Return the last item of *iterable*, or *default* if *iterable* is
empty.
>>> last([0, 1, 2, 3])
3
>>> last([], 'some default')
'some default'
If *default* is not provided and there are no items in the iterable,
raise ``ValueError``.
"""
return
# Work around https://bugs.python.org/issue38525
and :
return
return
return
"""Return the nth or the last item of *iterable*,
or *default* if *iterable* is empty.
>>> nth_or_last([0, 1, 2, 3], 2)
2
>>> nth_or_last([0, 1], 2)
1
>>> nth_or_last([], 0, 'some default')
'some default'
If *default* is not provided and there are no items in the iterable,
raise ``ValueError``.
"""
return
"""Wrap an iterator to allow lookahead and prepending elements.
Call :meth:`peek` on the result to get the value that will be returned
by :func:`next`. This won't advance the iterator:
>>> p = peekable(['a', 'b'])
>>> p.peek()
'a'
>>> next(p)
'a'
Pass :meth:`peek` a default value to return that instead of raising
``StopIteration`` when the iterator is exhausted.
>>> p = peekable([])
>>> p.peek('hi')
'hi'
peekables also offer a :meth:`prepend` method, which "inserts" items
at the head of the iterable:
>>> p = peekable([1, 2, 3])
>>> p.prepend(10, 11, 12)
>>> next(p)
10
>>> p.peek()
11
>>> list(p)
[11, 12, 1, 2, 3]
peekables can be indexed. Index 0 is the item that will be returned by
:func:`next`, index 1 is the item after that, and so on:
The values up to the given index will be cached.
>>> p = peekable(['a', 'b', 'c', 'd'])
>>> p[0]
'a'
>>> p[1]
'b'
>>> next(p)
'a'
Negative indexes are supported, but be aware that they will cache the
remaining items in the source iterator, which may require significant
storage.
To check whether a peekable is exhausted, check its truth value:
>>> p = peekable(['a', 'b'])
>>> if p: # peekable has items
... list(p)
['a', 'b']
>>> if not p: # peekable is exhausted
... list(p)
[]
"""
=
=
return
return False
return True
"""Return the item that will be next returned from ``next()``.
Return ``default`` if there are no items left. If ``default`` is not
provided, raise ``StopIteration``.
"""
return
return
"""Stack up items to be the next ones returned from ``next()`` or
``self.peek()``. The items will be returned in
first in, first out order::
>>> p = peekable([1, 2, 3])
>>> p.prepend(10, 11, 12)
>>> next(p)
10
>>> list(p)
[11, 12, 1, 2, 3]
It is possible, by prepending items, to "resurrect" a peekable that
previously raised ``StopIteration``.
>>> p = peekable([])
>>> next(p)
Traceback (most recent call last):
...
StopIteration
>>> p.prepend(1)
>>> next(p)
1
>>> next(p)
Traceback (most recent call last):
...
StopIteration
"""
return
return
# Normalize the slice's arguments
= 1
= 0
=
< 0:
= -1
=
# If either the start or stop index is negative, we'll need to cache
# the rest of the iterable in order to slice from the right side.
# Otherwise we'll need to find the rightmost index and cache to that
# point.
=
=
return
return
=
>= :
return
"""Return a sorted merge of the items from each of several already-sorted
*iterables*.
>>> list(collate('ACDZ', 'AZ', 'JKL'))
['A', 'A', 'C', 'D', 'J', 'K', 'L', 'Z', 'Z']
Works lazily, keeping only the next value from each iterable in memory. Use
:func:`collate` to, for example, perform a n-way mergesort of items that
don't fit in memory.
If a *key* function is specified, the iterables will be sorted according
to its result:
>>> key = lambda s: int(s) # Sort by numeric value, not by string
>>> list(collate(['1', '10'], ['2', '11'], key=key))
['1', '2', '10', '11']
If the *iterables* are sorted in descending order, set *reverse* to
``True``:
>>> list(collate([5, 3, 1], [4, 2, 0], reverse=True))
[5, 4, 3, 2, 1, 0]
If the elements of the passed-in iterables are out of order, you might get
unexpected results.
On Python 3.5+, this function is an alias for :func:`heapq.merge`.
"""
return
"""Decorator that automatically advances a PEP-342-style "reverse iterator"
to its first yield point so you don't have to call ``next()`` on it
manually.
>>> @consumer
... def tally():
... i = 0
... while True:
... print('Thing number %s is %s.' % (i, (yield)))
... i += 1
...
>>> t = tally()
>>> t.send('red')
Thing number 0 is red.
>>> t.send('fish')
Thing number 1 is fish.
Without the decorator, you would have to call ``next(t)`` before
``t.send()`` could be used.
"""
=
return
return
"""Return the number of items in *iterable*.
>>> ilen(x for x in range(1000000) if x % 3 == 0)
333334
This consumes the iterable, so handle with care.
"""
# This approach was selected because benchmarks showed it's likely the
# fastest of the known implementations at the time of writing.
# See GitHub tracker: #236, #230.
=
return
"""Return ``start``, ``func(start)``, ``func(func(start))``, ...
>>> from itertools import islice
>>> list(islice(iterate(lambda x: 2*x, 1), 10))
[1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
"""
yield
=
"""Wrap an iterable in a ``with`` statement, so it closes once exhausted.
For example, this will close the file when the iterator is exhausted::
upper_lines = (line.upper() for line in with_iter(open('foo')))
Any context manager which returns an iterable is a candidate for
``with_iter``.
"""
yield from
"""Return the first item from *iterable*, which is expected to contain only
that item. Raise an exception if *iterable* is empty or has more than one
item.
:func:`one` is useful for ensuring that an iterable contains only one item.
For example, it can be used to retrieve the result of a database query
that is expected to return a single row.
If *iterable* is empty, ``ValueError`` will be raised. You may specify a
different exception with the *too_short* keyword:
>>> it = []
>>> one(it) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
ValueError: too many items in iterable (expected 1)'
>>> too_short = IndexError('too few items')
>>> one(it, too_short=too_short) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
IndexError: too few items
Similarly, if *iterable* contains more than one item, ``ValueError`` will
be raised. You may specify a different exception with the *too_long*
keyword:
>>> it = ['too', 'many']
>>> one(it) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
ValueError: Expected exactly one item in iterable, but got 'too',
'many', and perhaps more.
>>> too_long = RuntimeError
>>> one(it, too_long=too_long) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
RuntimeError
Note that :func:`one` attempts to advance *iterable* twice to ensure there
is only one item. See :func:`spy` or :func:`peekable` to check iterable
contents less destructively.
"""
=
=
=
pass
=
return
"""Yield successive distinct permutations of the elements in *iterable*.
>>> sorted(distinct_permutations([1, 0, 1]))
[(0, 1, 1), (1, 0, 1), (1, 1, 0)]
Equivalent to ``set(permutations(iterable))``, except duplicates are not
generated and thrown away. For larger input sequences this is much more
efficient.
Duplicate permutations arise when there are duplicated elements in the
input iterable. The number of items returned is
`n! / (x_1! * x_2! * ... * x_n!)`, where `n` is the total number of
items input, and each `x_i` is the count of a distinct item in the input
sequence.
If *r* is given, only the *r*-length permutations are yielded.
>>> sorted(distinct_permutations([1, 0, 1], r=2))
[(0, 1), (1, 0), (1, 1)]
>>> sorted(distinct_permutations(range(3), r=2))
[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]
"""
# Algorithm: https://w.wiki/Qai
# Yield the permutation we have
yield
# Find the largest index i such that A[i] < A[i + 1]
break
# If no such index exists, this permutation is the last one
return
# Find the largest index j greater than j such that A[i] < A[j]
break
# Swap the value of A[i] with that of A[j], then reverse the
# sequence from A[i + 1] to form the new permutation
, = ,
= # A[i + 1:][::-1]
# Algorithm: modified from the above
# Split A into the first r items and the last r items
, = ,
=
=
# Yield the permutation we have
yield
# Starting from the right, find the first index of the head with
# value smaller than the maximum value of the tail - call it i.
=
break
=
return
# Starting from the left, find the first value of the tail
# with a value greater than head[i] and swap.
, = ,
break
# If we didn't find one, start from the right and find the first
# index of the head with a value greater than head[i] and swap.
, = ,
break
# Reverse head[i + 1:] and swap it with tail[:r - (i + 1)]
+= # head[i + 1:][::-1]
+= 1
, = ,
=
=
=
return
return
"""Intersperse filler element *e* among the items in *iterable*, leaving
*n* items between each filler element.
>>> list(intersperse('!', [1, 2, 3, 4, 5]))
[1, '!', 2, '!', 3, '!', 4, '!', 5]
>>> list(intersperse(None, [1, 2, 3, 4, 5], n=2))
[1, 2, None, 3, 4, None, 5]
"""
== 1:
# interleave(repeat(e), iterable) -> e, x_0, e, e, x_1, e, x_2...
# islice(..., 1, None) -> x_0, e, e, x_1, e, x_2...
return
# interleave(filler, chunks) -> [e], [x_0, x_1], [e], [x_2, x_3]...
# islice(..., 1, None) -> [x_0, x_1], [e], [x_2, x_3]...
# flatten(...) -> x_0, x_1, e, x_2, x_3...
=
=
return
"""Return the elements from each of the input iterables that aren't in the
other input iterables.
For example, suppose you have a set of packages, each with a set of
dependencies::
{'pkg_1': {'A', 'B'}, 'pkg_2': {'B', 'C'}, 'pkg_3': {'B', 'D'}}
If you remove one package, which dependencies can also be removed?
If ``pkg_1`` is removed, then ``A`` is no longer necessary - it is not
associated with ``pkg_2`` or ``pkg_3``. Similarly, ``C`` is only needed for
``pkg_2``, and ``D`` is only needed for ``pkg_3``::
>>> unique_to_each({'A', 'B'}, {'B', 'C'}, {'B', 'D'})
[['A'], ['C'], ['D']]
If there are duplicates in one input iterable that aren't in the others
they will be duplicated in the output. Input order is preserved::
>>> unique_to_each("mississippi", "missouri")
[['p', 'p'], ['o', 'u', 'r']]
It is assumed that the elements of each iterable are hashable.
"""
=
=
=
return
"""Return a sliding window of width *n* over the given iterable.
>>> all_windows = windowed([1, 2, 3, 4, 5], 3)
>>> list(all_windows)
[(1, 2, 3), (2, 3, 4), (3, 4, 5)]
When the window is larger than the iterable, *fillvalue* is used in place
of missing values:
>>> list(windowed([1, 2, 3], 4))
[(1, 2, 3, None)]
Each window will advance in increments of *step*:
>>> list(windowed([1, 2, 3, 4, 5, 6], 3, fillvalue='!', step=2))
[(1, 2, 3), (3, 4, 5), (5, 6, '!')]
To slide into the iterable's items, use :func:`chain` to add filler items
to the left:
>>> iterable = [1, 2, 3, 4]
>>> n = 3
>>> padding = [None] * (n - 1)
>>> list(windowed(chain(padding, iterable), 3))
[(None, None, 1), (None, 1, 2), (1, 2, 3), (2, 3, 4)]
"""
yield
return
=
=
-= 1
=
yield
=
yield
0 < < :
+= *
yield
"""Yield all of the substrings of *iterable*.
>>> [''.join(s) for s in substrings('more')]
['m', 'o', 'r', 'e', 'mo', 'or', 're', 'mor', 'ore', 'more']
Note that non-string iterables can also be subdivided.
>>> list(substrings([0, 1, 2]))
[(0,), (1,), (2,), (0, 1), (1, 2), (0, 1, 2)]
"""
# The length-1 substrings
=
yield
=
=
# And the rest
yield
"""Yield all substrings and their positions in *seq*
The items yielded will be a tuple of the form ``(substr, i, j)``, where
``substr == seq[i:j]``.
This function only works for iterables that support slicing, such as
``str`` objects.
>>> for item in substrings_indexes('more'):
... print(item)
('m', 0, 1)
('o', 1, 2)
('r', 2, 3)
('e', 3, 4)
('mo', 0, 2)
('or', 1, 3)
('re', 2, 4)
('mor', 0, 3)
('ore', 1, 4)
('more', 0, 4)
Set *reverse* to ``True`` to yield the same items in the opposite order.
"""
=
=
return
"""Wrap *iterable* and return an object that buckets it iterable into
child iterables based on a *key* function.
>>> iterable = ['a1', 'b1', 'c1', 'a2', 'b2', 'c2', 'b3']
>>> s = bucket(iterable, key=lambda x: x[0]) # Bucket by 1st character
>>> sorted(list(s)) # Get the keys
['a', 'b', 'c']
>>> a_iterable = s['a']
>>> next(a_iterable)
'a1'
>>> next(a_iterable)
'a2'
>>> list(s['b'])
['b1', 'b2', 'b3']
The original iterable will be advanced and its items will be cached until
they are used by the child iterables. This may require significant storage.
By default, attempting to select a bucket to which no items belong will
exhaust the iterable and cache all values.
If you specify a *validator* function, selected buckets will instead be
checked against it.
>>> from itertools import count
>>> it = count(1, 2) # Infinite sequence of odd numbers
>>> key = lambda x: x % 10 # Bucket by last digit
>>> validator = lambda x: x in {1, 3, 5, 7, 9} # Odd digits only
>>> s = bucket(it, key=key, validator=validator)
>>> 2 in s
False
>>> list(s[2])
[]
"""
=
=
=
= or
return False
=
return False
return True
"""
Helper to yield items from the parent iterator that match *value*.
Items that don't match are stored in the local cache as they
are encountered.
"""
# If we've cached some items that match the target value, emit
# the first one and evict it from the cache.
yield
# Otherwise we need to advance the parent iterator to search for
# a matching item, caching the rest.
=
return
=
yield
break
:
=
yield from
return
return
"""Return a 2-tuple with a list containing the first *n* elements of
*iterable*, and an iterator with the same items as *iterable*.
This allows you to "look ahead" at the items in the iterable without
advancing it.
There is one item in the list by default:
>>> iterable = 'abcdefg'
>>> head, iterable = spy(iterable)
>>> head
['a']
>>> list(iterable)
['a', 'b', 'c', 'd', 'e', 'f', 'g']
You may use unpacking to retrieve items instead of lists:
>>> (head,), iterable = spy('abcdefg')
>>> head
'a'
>>> (first, second), iterable = spy('abcdefg', 2)
>>> first
'a'
>>> second
'b'
The number of items requested can be larger than the number of items in
the iterable:
>>> iterable = [1, 2, 3, 4, 5]
>>> head, iterable = spy(iterable, 10)
>>> head
[1, 2, 3, 4, 5]
>>> list(iterable)
[1, 2, 3, 4, 5]
"""
=
=
return ,
"""Return a new iterable yielding from each iterable in turn,
until the shortest is exhausted.
>>> list(interleave([1, 2, 3], [4, 5], [6, 7, 8]))
[1, 4, 6, 2, 5, 7]
For a version that doesn't terminate after the shortest iterable is
exhausted, see :func:`interleave_longest`.
"""
return
"""Return a new iterable yielding from each iterable in turn,
skipping any that are exhausted.
>>> list(interleave_longest([1, 2, 3], [4, 5], [6, 7, 8]))
[1, 4, 6, 2, 5, 7, 3, 8]
This function produces the same output as :func:`roundrobin`, but may
perform better for some inputs (in particular when the number of iterables
is large).
"""
=
return
"""Flatten an iterable with multiple levels of nesting (e.g., a list of
lists of tuples) into non-iterable types.
>>> iterable = [(1, 2), ([3, 4], [[5], [6]])]
>>> list(collapse(iterable))
[1, 2, 3, 4, 5, 6]
Binary and text strings are not considered iterable and
will not be collapsed.
To avoid collapsing other types, specify *base_type*:
>>> iterable = ['ab', ('cd', 'ef'), ['gh', 'ij']]
>>> list(collapse(iterable, base_type=tuple))
['ab', ('cd', 'ef'), 'gh', 'ij']
Specify *levels* to stop flattening after a certain level:
>>> iterable = [('a', ['b']), ('c', ['d'])]
>>> list(collapse(iterable)) # Fully flattened
['a', 'b', 'c', 'd']
>>> list(collapse(iterable, levels=1)) # Only one level flattened
['a', ['b'], 'c', ['d']]
"""
yield
return
=
yield
return
yield from
yield from
"""Invoke *func* on each item in *iterable* (or on each *chunk_size* group
of items) before yielding the item.
`func` must be a function that takes a single argument. Its return value
will be discarded.
*before* and *after* are optional functions that take no arguments. They
will be executed before iteration starts and after it ends, respectively.
`side_effect` can be used for logging, updating progress bars, or anything
that is not functionally "pure."
Emitting a status message:
>>> from more_itertools import consume
>>> func = lambda item: print('Received {}'.format(item))
>>> consume(side_effect(func, range(2)))
Received 0
Received 1
Operating on chunks of items:
>>> pair_sums = []
>>> func = lambda chunk: pair_sums.append(sum(chunk))
>>> list(side_effect(func, [0, 1, 2, 3, 4, 5], 2))
[0, 1, 2, 3, 4, 5]
>>> list(pair_sums)
[1, 5, 9]
Writing to a file-like object:
>>> from io import StringIO
>>> from more_itertools import consume
>>> f = StringIO()
>>> func = lambda x: print(x, file=f)
>>> before = lambda: print(u'HEADER', file=f)
>>> after = f.close
>>> it = [u'a', u'b', u'c']
>>> consume(side_effect(func, it, before=before, after=after))
>>> f.closed
True
"""
yield
yield from
"""Yield slices of length *n* from the sequence *seq*.
>>> list(sliced((1, 2, 3, 4, 5, 6), 3))
[(1, 2, 3), (4, 5, 6)]
By the default, the last yielded slice will have fewer than *n* elements
if the length of *seq* is not divisible by *n*:
>>> list(sliced((1, 2, 3, 4, 5, 6, 7, 8), 3))
[(1, 2, 3), (4, 5, 6), (7, 8)]
If the length of *seq* is not divisible by *n* and *strict* is
``True``, then ``ValueError`` will be raised before the last
slice is yielded.
This function will only work for iterables that support slicing.
For non-sliceable iterables, see :func:`chunked`.
"""
=
yield
return
return
"""Yield lists of items from *iterable*, where each list is delimited by
an item where callable *pred* returns ``True``.
>>> list(split_at('abcdcba', lambda x: x == 'b'))
[['a'], ['c', 'd', 'c'], ['a']]
>>> list(split_at(range(10), lambda n: n % 2 == 1))
[[0], [2], [4], [6], [8], []]
At most *maxsplit* splits are done. If *maxsplit* is not specified or -1,
then there is no limit on the number of splits:
>>> list(split_at(range(10), lambda n: n % 2 == 1, maxsplit=2))
[[0], [2], [4, 5, 6, 7, 8, 9]]
By default, the delimiting items are not included in the output.
The include them, set *keep_separator* to ``True``.
>>> list(split_at('abcdcba', lambda x: x == 'b', keep_separator=True))
[['a'], ['b'], ['c', 'd', 'c'], ['b'], ['a']]
"""
yield
return
=
=
yield
yield
yield
return
=
-= 1
yield
"""Yield lists of items from *iterable*, where each list ends just before
an item for which callable *pred* returns ``True``:
>>> list(split_before('OneTwo', lambda s: s.isupper()))
[['O', 'n', 'e'], ['T', 'w', 'o']]
>>> list(split_before(range(10), lambda n: n % 3 == 0))
[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]]
At most *maxsplit* splits are done. If *maxsplit* is not specified or -1,
then there is no limit on the number of splits:
>>> list(split_before(range(10), lambda n: n % 3 == 0, maxsplit=2))
[[0, 1, 2], [3, 4, 5], [6, 7, 8, 9]]
"""
yield
return
=
=
yield
yield +
return
=
-= 1
yield
"""Yield lists of items from *iterable*, where each list ends with an
item where callable *pred* returns ``True``:
>>> list(split_after('one1two2', lambda s: s.isdigit()))
[['o', 'n', 'e', '1'], ['t', 'w', 'o', '2']]
>>> list(split_after(range(10), lambda n: n % 3 == 0))
[[0], [1, 2, 3], [4, 5, 6], [7, 8, 9]]
At most *maxsplit* splits are done. If *maxsplit* is not specified or -1,
then there is no limit on the number of splits:
>>> list(split_after(range(10), lambda n: n % 3 == 0, maxsplit=2))
[[0], [1, 2, 3], [4, 5, 6, 7, 8, 9]]
"""
yield
return
=
=
yield
yield
return
=
-= 1
yield
"""Split *iterable* into pieces based on the output of *pred*.
*pred* should be a function that takes successive pairs of items and
returns ``True`` if the iterable should be split in between them.
For example, to find runs of increasing numbers, split the iterable when
element ``i`` is larger than element ``i + 1``:
>>> list(split_when([1, 2, 3, 3, 2, 5, 2, 4, 2], lambda x, y: x > y))
[[1, 2, 3, 3], [2, 5], [2, 4], [2]]
At most *maxsplit* splits are done. If *maxsplit* is not specified or -1,
then there is no limit on the number of splits:
>>> list(split_when([1, 2, 3, 3, 2, 5, 2, 4, 2],
... lambda x, y: x > y, maxsplit=2))
[[1, 2, 3, 3], [2, 5], [2, 4, 2]]
"""
yield
return
=
=
return
=
yield
yield +
return
=
-= 1
=
yield
"""Yield a list of sequential items from *iterable* of length 'n' for each
integer 'n' in *sizes*.
>>> list(split_into([1,2,3,4,5,6], [1,2,3]))
[[1], [2, 3], [4, 5, 6]]
If the sum of *sizes* is smaller than the length of *iterable*, then the
remaining items of *iterable* will not be returned.
>>> list(split_into([1,2,3,4,5,6], [2,3]))
[[1, 2], [3, 4, 5]]
If the sum of *sizes* is larger than the length of *iterable*, fewer items
will be returned in the iteration that overruns *iterable* and further
lists will be empty:
>>> list(split_into([1,2,3,4], [1,2,3,4]))
[[1], [2, 3], [4], []]
When a ``None`` object is encountered in *sizes*, the returned list will
contain items up to the end of *iterable* the same way that itertools.slice
does:
>>> list(split_into([1,2,3,4,5,6,7,8,9,0], [2,3,None]))
[[1, 2], [3, 4, 5], [6, 7, 8, 9, 0]]
:func:`split_into` can be useful for grouping a series of items where the
sizes of the groups are not uniform. An example would be where in a row
from a table, multiple columns represent elements of the same feature
(e.g. a point represented by x,y,z) but, the format is not the same for
all columns.
"""
# convert the iterable argument into an iterator so its contents can
# be consumed by islice in case it is a generator
=
yield
return
yield
"""Yield the elements from *iterable*, followed by *fillvalue*, such that
at least *n* items are emitted.
>>> list(padded([1, 2, 3], '?', 5))
[1, 2, 3, '?', '?']
If *next_multiple* is ``True``, *fillvalue* will be emitted until the
number of items emitted is a multiple of *n*::
>>> list(padded([1, 2, 3, 4], n=3, next_multiple=True))
[1, 2, 3, 4, None, None]
If *n* is ``None``, *fillvalue* will be emitted indefinitely.
"""
=
yield from
< 1:
= 0
yield
+= 1
= %
yield
"""After the *iterable* is exhausted, keep yielding its last element.
>>> list(islice(repeat_last(range(3)), 5))
[0, 1, 2, 2, 2]
If the iterable is empty, yield *default* forever::
>>> list(islice(repeat_last(range(0), 42), 5))
[42, 42, 42, 42, 42]
"""
=
yield
=
yield from
"""Distribute the items from *iterable* among *n* smaller iterables.
>>> group_1, group_2 = distribute(2, [1, 2, 3, 4, 5, 6])
>>> list(group_1)
[1, 3, 5]
>>> list(group_2)
[2, 4, 6]
If the length of *iterable* is not evenly divisible by *n*, then the
length of the returned iterables will not be identical:
>>> children = distribute(3, [1, 2, 3, 4, 5, 6, 7])
>>> [list(c) for c in children]
[[1, 4, 7], [2, 5], [3, 6]]
If the length of *iterable* is smaller than *n*, then the last returned
iterables will be empty:
>>> children = distribute(5, [1, 2, 3])
>>> [list(c) for c in children]
[[1], [2], [3], [], []]
This function uses :func:`itertools.tee` and may require significant
storage. If you need the order items in the smaller iterables to match the
original iterable, see :func:`divide`.
"""
=
return
"""Yield tuples whose elements are offset from *iterable*.
The amount by which the `i`-th item in each tuple is offset is given by
the `i`-th item in *offsets*.
>>> list(stagger([0, 1, 2, 3]))
[(None, 0, 1), (0, 1, 2), (1, 2, 3)]
>>> list(stagger(range(8), offsets=(0, 2, 4)))
[(0, 2, 4), (1, 3, 5), (2, 4, 6), (3, 5, 7)]
By default, the sequence will end when the final element of a tuple is the
last item in the iterable. To continue until the first element of a tuple
is the last item in the iterable, set *longest* to ``True``::
>>> list(stagger([0, 1, 2, 3], longest=True))
[(None, 0, 1), (0, 1, 2), (1, 2, 3), (2, 3, None), (3, None, None)]
By default, ``None`` will be used to replace offsets beyond the end of the
sequence. Specify *fillvalue* to use some other value.
"""
=
return
=
+=
yield
"""``zip`` the input *iterables* together, but raise
``UnequalIterablesError`` if they aren't all the same length.
>>> it_1 = range(3)
>>> it_2 = iter('abc')
>>> list(zip_equal(it_1, it_2))
[(0, 'a'), (1, 'b'), (2, 'c')]
>>> it_1 = range(3)
>>> it_2 = iter('abcd')
>>> list(zip_equal(it_1, it_2)) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
more_itertools.more.UnequalIterablesError: Iterables have different
lengths
"""
# Check whether the iterables are all the same size.
=
=
break
# If we didn't break out, we can use the built-in zip.
return
# If we did break out, there was a mismatch.
# If any one of the iterables didn't have a length, start reading
# them until one runs out.
return
"""``zip`` the input *iterables* together, but offset the `i`-th iterable
by the `i`-th item in *offsets*.
>>> list(zip_offset('0123', 'abcdef', offsets=(0, 1)))
[('0', 'b'), ('1', 'c'), ('2', 'd'), ('3', 'e')]
This can be used as a lightweight alternative to SciPy or pandas to analyze
data sets in which some series have a lead or lag relationship.
By default, the sequence will end when the shortest iterable is exhausted.
To continue until the longest iterable is exhausted, set *longest* to
``True``.
>>> list(zip_offset('0123', 'abcdef', offsets=(0, 1), longest=True))
[('0', 'b'), ('1', 'c'), ('2', 'd'), ('3', 'e'), (None, 'f')]
By default, ``None`` will be used to replace offsets beyond the end of the
sequence. Specify *fillvalue* to use some other value.
"""
=
> 0:
return
return
"""Return the input iterables sorted together, with *key_list* as the
priority for sorting. All iterables are trimmed to the length of the
shortest one.
This can be used like the sorting function in a spreadsheet. If each
iterable represents a column of data, the key list determines which
columns are used for sorting.
By default, all iterables are sorted using the ``0``-th iterable::
>>> iterables = [(4, 3, 2, 1), ('a', 'b', 'c', 'd')]
>>> sort_together(iterables)
[(1, 2, 3, 4), ('d', 'c', 'b', 'a')]
Set a different key list to sort according to another iterable.
Specifying multiple keys dictates how ties are broken::
>>> iterables = [(3, 1, 2), (0, 1, 0), ('c', 'b', 'a')]
>>> sort_together(iterables, key_list=(1, 2))
[(2, 3, 1), (0, 0, 1), ('a', 'c', 'b')]
To sort by a function of the elements of the iterable, pass a *key*
function. Its arguments are the elements of the iterables corresponding to
the key list::
>>> names = ('a', 'b', 'c')
>>> lengths = (1, 2, 3)
>>> widths = (5, 2, 1)
>>> def area(length, width):
... return length * width
>>> sort_together([names, lengths, widths], key_list=(1, 2), key=area)
[('c', 'b', 'a'), (3, 2, 1), (1, 2, 5)]
Set *reverse* to ``True`` to sort in descending order.
>>> sort_together([(1, 2, 3), ('c', 'b', 'a')], reverse=True)
[(3, 2, 1), ('a', 'b', 'c')]
"""
# if there is no key function, the key argument to sorted is an
# itemgetter
=
# if there is a key function, call it with the items at the offsets
# specified by the key function as arguments
=
# if key_list contains a single item, pass the item at that offset
# as the only argument to the key function
=
=
# if key_list contains multiple items, use itemgetter to return a
# tuple of items, which we pass as *args to the key function
=
=
return
"""The inverse of :func:`zip`, this function disaggregates the elements
of the zipped *iterable*.
The ``i``-th iterable contains the ``i``-th element from each element
of the zipped iterable. The first element is used to to determine the
length of the remaining elements.
>>> iterable = [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
>>> letters, numbers = unzip(iterable)
>>> list(letters)
['a', 'b', 'c', 'd']
>>> list(numbers)
[1, 2, 3, 4]
This is similar to using ``zip(*iterable)``, but it avoids reading
*iterable* into memory. Note, however, that this function uses
:func:`itertools.tee` and thus may require significant storage.
"""
, =
# empty iterable, e.g. zip([], [], [])
return
# spy returns a one-length iterable as head
=
=
return
# basically if we have an iterable like
# iter([(1, 2, 3), (4, 5), (6,)])
# the second unzipped iterable would fail at the third tuple
# since it would try to access tup[1]
# same with the third unzipped iterable and the second tuple
# to support these "improperly zipped" iterables,
# we create a custom itemgetter
# which just stops the unzipped iterables
# at first length mismatch
return
return
"""Divide the elements from *iterable* into *n* parts, maintaining
order.
>>> group_1, group_2 = divide(2, [1, 2, 3, 4, 5, 6])
>>> list(group_1)
[1, 2, 3]
>>> list(group_2)
[4, 5, 6]
If the length of *iterable* is not evenly divisible by *n*, then the
length of the returned iterables will not be identical:
>>> children = divide(3, [1, 2, 3, 4, 5, 6, 7])
>>> [list(c) for c in children]
[[1, 2, 3], [4, 5], [6, 7]]
If the length of the iterable is smaller than n, then the last returned
iterables will be empty:
>>> children = divide(5, [1, 2, 3])
>>> [list(c) for c in children]
[[1], [2], [3], [], []]
This function will exhaust the iterable before returning and may require
significant storage. If order is not important, see :func:`distribute`,
which does not first pull the iterable into memory.
"""
=
=
, =
=
= 0
=
+= + 1
return
"""If *obj* is iterable, return an iterator over its items::
>>> obj = (1, 2, 3)
>>> list(always_iterable(obj))
[1, 2, 3]
If *obj* is not iterable, return a one-item iterable containing *obj*::
>>> obj = 1
>>> list(always_iterable(obj))
[1]
If *obj* is ``None``, return an empty iterable:
>>> obj = None
>>> list(always_iterable(None))
[]
By default, binary and text strings are not considered iterable::
>>> obj = 'foo'
>>> list(always_iterable(obj))
['foo']
If *base_type* is set, objects for which ``isinstance(obj, base_type)``
returns ``True`` won't be considered iterable.
>>> obj = {'a': 1}
>>> list(always_iterable(obj)) # Iterate over the dict's keys
['a']
>>> list(always_iterable(obj, base_type=dict)) # Treat dicts as a unit
[{'a': 1}]
Set *base_type* to ``None`` to avoid any special handling and treat objects
Python considers iterable as iterable:
>>> obj = 'foo'
>>> list(always_iterable(obj, base_type=None))
['f', 'o', 'o']
"""
return
return
return
return
"""Return an iterable over `(bool, item)` tuples where the `item` is
drawn from *iterable* and the `bool` indicates whether
that item satisfies the *predicate* or is adjacent to an item that does.
For example, to find whether items are adjacent to a ``3``::
>>> list(adjacent(lambda x: x == 3, range(6)))
[(False, 0), (False, 1), (True, 2), (True, 3), (True, 4), (False, 5)]
Set *distance* to change what counts as adjacent. For example, to find
whether items are two places away from a ``3``:
>>> list(adjacent(lambda x: x == 3, range(6), distance=2))
[(False, 0), (True, 1), (True, 2), (True, 3), (True, 4), (True, 5)]
This is useful for contextualizing the results of a search function.
For example, a code comparison tool might want to identify lines that
have changed, but also surrounding lines to give the viewer of the diff
context.
The predicate function will only be called once for each item in the
iterable.
See also :func:`groupby_transform`, which can be used with this function
to group ranges of items with the same `bool` value.
"""
# Allow distance=0 mainly for testing that it reproduces results with map()
, =
= *
=
=
return
"""An extension of :func:`itertools.groupby` that can apply transformations
to the grouped data.
* *keyfunc* is a function computing a key value for each item in *iterable*
* *valuefunc* is a function that transforms the individual items from
*iterable* after grouping
* *reducefunc* is a function that transforms each group of items
>>> iterable = 'aAAbBBcCC'
>>> keyfunc = lambda k: k.upper()
>>> valuefunc = lambda v: v.lower()
>>> reducefunc = lambda g: ''.join(g)
>>> list(groupby_transform(iterable, keyfunc, valuefunc, reducefunc))
[('A', 'aaa'), ('B', 'bbb'), ('C', 'ccc')]
Each optional argument defaults to an identity function if not specified.
:func:`groupby_transform` is useful when grouping elements of an iterable
using a separate iterable as the key. To do this, :func:`zip` the iterables
and pass a *keyfunc* that extracts the first element and a *valuefunc*
that extracts the second element::
>>> from operator import itemgetter
>>> keys = [0, 0, 1, 1, 1, 2, 2, 2, 3]
>>> values = 'abcdefghi'
>>> iterable = zip(keys, values)
>>> grouper = groupby_transform(iterable, itemgetter(0), itemgetter(1))
>>> [(k, ''.join(g)) for k, g in grouper]
[(0, 'ab'), (1, 'cde'), (2, 'fgh'), (3, 'i')]
Note that the order of items in the iterable is significant.
Only adjacent items are grouped together, so if you don't want any
duplicate groups, you should sort the iterable by the key function.
"""
=
=
=
return
"""An extension of the built-in ``range()`` function whose arguments can
be any orderable numeric type.
With only *stop* specified, *start* defaults to ``0`` and *step*
defaults to ``1``. The output items will match the type of *stop*:
>>> list(numeric_range(3.5))
[0.0, 1.0, 2.0, 3.0]
With only *start* and *stop* specified, *step* defaults to ``1``. The
output items will match the type of *start*:
>>> from decimal import Decimal
>>> start = Decimal('2.1')
>>> stop = Decimal('5.1')
>>> list(numeric_range(start, stop))
[Decimal('2.1'), Decimal('3.1'), Decimal('4.1')]
With *start*, *stop*, and *step* specified the output items will match
the type of ``start + step``:
>>> from fractions import Fraction
>>> start = Fraction(1, 2) # Start at 1/2
>>> stop = Fraction(5, 2) # End at 5/2
>>> step = Fraction(1, 2) # Count by 1/2
>>> list(numeric_range(start, stop, step))
[Fraction(1, 2), Fraction(1, 1), Fraction(3, 2), Fraction(2, 1)]
If *step* is zero, ``ValueError`` is raised. Negative steps are supported:
>>> list(numeric_range(3, -1, -1.0))
[3.0, 2.0, 1.0, 0.0]
Be aware of the limitations of floating point numbers; the representation
of the yielded numbers may be surprising.
``datetime.datetime`` objects can be used for *start* and *stop*, if *step*
is a ``datetime.timedelta`` object:
>>> import datetime
>>> start = datetime.datetime(2019, 1, 1)
>>> stop = datetime.datetime(2019, 1, 3)
>>> step = datetime.timedelta(days=1)
>>> items = iter(numeric_range(start, stop, step))
>>> next(items)
datetime.datetime(2019, 1, 1, 0, 0)
>>> next(items)
datetime.datetime(2019, 1, 2, 0, 0)
"""
=
=
=
=
=
== 2:
, =
=
== 3:
, , =
== 0:
=
= >
return <
return >
return % ==
return % ==
return False
= not
= not
return and # True if both empty
return
return False
return
:
=
=
>= :
=
# -self._len < key.start < self._len
=
=
<= -:
=
# -self._len < key.stop < self._len
=
return
return
return
=
return
return
return
=
=
=
=
=
= -
= -
= 0
# distance > 0 and step > 0: regular euclidean division
, =
= +
return ,
return
return
return
return
, =
return
, =
return
+=
return + *
"""Cycle through the items from *iterable* up to *n* times, yielding
the number of completed cycles along with each item. If *n* is omitted the
process repeats indefinitely.
>>> list(count_cycle('AB', 3))
[(0, 'A'), (0, 'B'), (1, 'A'), (1, 'B'), (2, 'A'), (2, 'B')]
"""
=
return
=
return
"""Yield 3-tuples of the form ``(is_first, is_last, item)``.
>>> list(mark_ends('ABC'))
[(True, False, 'A'), (False, False, 'B'), (False, True, 'C')]
Use this when looping over an iterable to take special action on its first
and/or last items:
>>> iterable = ['Header', 100, 200, 'Footer']
>>> total = 0
>>> for is_first, is_last, item in mark_ends(iterable):
... if is_first:
... continue # Skip the header
... if is_last:
... continue # Skip the footer
... total += item
>>> print(total)
300
"""
=
=
return
=
=
yield == 0, False,
yield == 0, True,
"""Yield the index of each item in *iterable* for which *pred* returns
``True``.
*pred* defaults to :func:`bool`, which will select truthy items:
>>> list(locate([0, 1, 1, 0, 1, 0, 0]))
[1, 2, 4]
Set *pred* to a custom function to, e.g., find the indexes for a particular
item.
>>> list(locate(['a', 'b', 'c', 'b'], lambda x: x == 'b'))
[1, 3]
If *window_size* is given, then the *pred* function will be called with
that many items. This enables searching for sub-sequences:
>>> iterable = [0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3]
>>> pred = lambda *args: args == (1, 2, 3)
>>> list(locate(iterable, pred=pred, window_size=3))
[1, 5, 9]
Use with :func:`seekable` to find indexes and then retrieve the associated
items:
>>> from itertools import count
>>> from more_itertools import seekable
>>> source = (3 * n + 1 if (n % 2) else n // 2 for n in count())
>>> it = seekable(source)
>>> pred = lambda x: x > 100
>>> indexes = locate(it, pred=pred)
>>> i = next(indexes)
>>> it.seek(i)
>>> next(it)
106
"""
return
=
return
"""Yield the items from *iterable*, but strip any from the beginning
for which *pred* returns ``True``.
For example, to remove a set of items from the start of an iterable:
>>> iterable = (None, False, None, 1, 2, None, 3, False, None)
>>> pred = lambda x: x in {None, False, ''}
>>> list(lstrip(iterable, pred))
[1, 2, None, 3, False, None]
This function is analogous to to :func:`str.lstrip`, and is essentially
an wrapper for :func:`itertools.dropwhile`.
"""
return
"""Yield the items from *iterable*, but strip any from the end
for which *pred* returns ``True``.
For example, to remove a set of items from the end of an iterable:
>>> iterable = (None, False, None, 1, 2, None, 3, False, None)
>>> pred = lambda x: x in {None, False, ''}
>>> list(rstrip(iterable, pred))
[None, False, None, 1, 2, None, 3]
This function is analogous to :func:`str.rstrip`.
"""
=
=
=
yield from
yield
"""Yield the items from *iterable*, but strip any from the
beginning and end for which *pred* returns ``True``.
For example, to remove a set of items from both ends of an iterable:
>>> iterable = (None, False, None, 1, 2, None, 3, False, None)
>>> pred = lambda x: x in {None, False, ''}
>>> list(strip(iterable, pred))
[1, 2, None, 3]
This function is analogous to :func:`str.strip`.
"""
return
"""An extension of :func:`itertools.islice` that supports negative values
for *stop*, *start*, and *step*.
>>> iterable = iter('abcdefgh')
>>> list(islice_extended(iterable, -4, -1))
['e', 'f', 'g']
Slices with negative values require some caching of *iterable*, but this
function takes care to minimize the amount of memory required.
For example, you can use a negative step with an infinite iterator:
>>> from itertools import count
>>> list(islice_extended(count(), 110, 99, -2))
[110, 108, 106, 104, 102, 100]
You can also use slice notation directly:
>>> iterable = map(str, count())
>>> it = islice_extended(iterable)[10:20:2]
>>> list(it)
['10', '12', '14', '16', '18']
"""
=
=
=
return
return
return
=
=
= or 1
= 0
# Consume all but the last -start items
=
=
# Adjust start to be positive
=
# Adjust stop to be positive
=
>= 0:
=
=
# Slice the cache
= -
return
yield
and :
# Advance to the start position
# When stop is negative, we have to carry -stop items while
# iterating
=
=
yield
# When both start and stop are positive we have the normal case
yield from
= -1
# Consume all but the last items
= - - 1
=
=
# If start and stop are both negative they are comparable and
# we can just slice. Otherwise we can adjust start to be negative
# and then slice.
, = ,
, = , None
yield
# Advance to the stop position
= + 1
# stop is positive, so if start is negative they are not comparable
# and we need the rest of the items.
=
= None
# stop is None and start is positive, so we just need items up to
# the start index.
is None:
= None
= + 1
# Both stop and start are positive, so they are comparable.
= None
= -
return
=
yield from
"""An extension of :func:`reversed` that supports all iterables, not
just those which implement the ``Reversible`` or ``Sequence`` protocols.
>>> print(*always_reversible(x for x in range(3)))
2 1 0
If the iterable is already reversible, this function returns the
result of :func:`reversed()`. If the iterable is not reversible,
this function will cache the remaining items in the iterable and
yield them in reverse order, which may require significant storage.
"""
return
return
"""Yield groups of consecutive items using :func:`itertools.groupby`.
The *ordering* function determines whether two items are adjacent by
returning their position.
By default, the ordering function is the identity function. This is
suitable for finding runs of numbers:
>>> iterable = [1, 10, 11, 12, 20, 30, 31, 32, 33, 40]
>>> for group in consecutive_groups(iterable):
... print(list(group))
[1]
[10, 11, 12]
[20]
[30, 31, 32, 33]
[40]
For finding runs of adjacent letters, try using the :meth:`index` method
of a string of letters:
>>> from string import ascii_lowercase
>>> iterable = 'abcdfgilmnop'
>>> ordering = ascii_lowercase.index
>>> for group in consecutive_groups(iterable, ordering):
... print(list(group))
['a', 'b', 'c', 'd']
['f', 'g']
['i']
['l', 'm', 'n', 'o', 'p']
Each group of consecutive items is an iterator that shares it source with
*iterable*. When an an output group is advanced, the previous group is
no longer available unless its elements are copied (e.g., into a ``list``).
>>> iterable = [1, 2, 11, 12, 21, 22]
>>> saved_groups = []
>>> for group in consecutive_groups(iterable):
... saved_groups.append(list(group)) # Copy group elements
>>> saved_groups
[[1, 2], [11, 12], [21, 22]]
"""
yield
"""This function is the inverse of :func:`itertools.accumulate`. By default
it will compute the first difference of *iterable* using
:func:`operator.sub`:
>>> from itertools import accumulate
>>> iterable = accumulate([0, 1, 2, 3, 4]) # produces 0, 1, 3, 6, 10
>>> list(difference(iterable))
[0, 1, 2, 3, 4]
*func* defaults to :func:`operator.sub`, but other functions can be
specified. They will be applied as follows::
A, B, C, D, ... --> A, func(B, A), func(C, B), func(D, C), ...
For example, to do progressive division:
>>> iterable = [1, 2, 6, 24, 120]
>>> func = lambda x, y: x // y
>>> list(difference(iterable, func))
[1, 2, 3, 4, 5]
If the *initial* keyword is set, the first element will be skipped when
computing successive differences.
>>> it = [10, 11, 13, 16] # from accumulate([1, 2, 3], initial=10)
>>> list(difference(it, initial=10))
[1, 2, 3]
"""
, =
=
return
=
return
"""Return a read-only view of the sequence object *target*.
:class:`SequenceView` objects are analogous to Python's built-in
"dictionary view" types. They provide a dynamic view of a sequence's items,
meaning that when the sequence updates, so does the view.
>>> seq = ['0', '1', '2']
>>> view = SequenceView(seq)
>>> view
SequenceView(['0', '1', '2'])
>>> seq.append('3')
>>> view
SequenceView(['0', '1', '2', '3'])
Sequence views support indexing, slicing, and length queries. They act
like the underlying sequence, except they don't allow assignment:
>>> view[1]
'1'
>>> view[1:-1]
['1', '2']
>>> len(view)
4
Sequence views are useful as an alternative to copying, as they don't
require (much) extra storage.
"""
=
return
return
return
"""Wrap an iterator to allow for seeking backward and forward. This
progressively caches the items in the source iterable so they can be
re-visited.
Call :meth:`seek` with an index to seek to that position in the source
iterable.
To "reset" an iterator, seek to ``0``:
>>> from itertools import count
>>> it = seekable((str(n) for n in count()))
>>> next(it), next(it), next(it)
('0', '1', '2')
>>> it.seek(0)
>>> next(it), next(it), next(it)
('0', '1', '2')
>>> next(it)
'3'
You can also seek forward:
>>> it = seekable((str(n) for n in range(20)))
>>> it.seek(10)
>>> next(it)
'10'
>>> it.seek(20) # Seeking past the end of the source isn't a problem
>>> list(it)
[]
>>> it.seek(0) # Resetting works even after hitting the end
>>> next(it), next(it), next(it)
('0', '1', '2')
Call :meth:`peek` to look ahead one item without advancing the iterator:
>>> it = seekable('1234')
>>> it.peek()
'1'
>>> list(it)
['1', '2', '3', '4']
>>> it.peek(default='empty')
'empty'
Before the iterator is at its end, calling :func:`bool` on it will return
``True``. After it will return ``False``:
>>> it = seekable('5678')
>>> bool(it)
True
>>> list(it)
['5', '6', '7', '8']
>>> bool(it)
False
You may view the contents of the cache with the :meth:`elements` method.
That returns a :class:`SequenceView`, a view that updates automatically:
>>> it = seekable((str(n) for n in range(10)))
>>> next(it), next(it), next(it)
('0', '1', '2')
>>> elements = it.elements()
>>> elements
SequenceView(['0', '1', '2'])
>>> next(it)
'3'
>>> elements
SequenceView(['0', '1', '2', '3'])
By default, the cache grows as the source iterable progresses, so beware of
wrapping very large or infinite iterables. Supply *maxlen* to limit the
size of the cache (this of course limits how far back you can seek).
>>> from itertools import count
>>> it = seekable((str(n) for n in count()), maxlen=2)
>>> next(it), next(it), next(it), next(it)
('0', '1', '2', '3')
>>> list(it.elements())
['2', '3']
>>> it.seek(0)
>>> next(it), next(it), next(it), next(it)
('2', '3', '4', '5')
>>> next(it)
'6'
"""
=
=
=
= None
return
=
= None
+= 1
return
=
return
return False
return True
=
return
=
-= 1
return
return
=
= -
"""
:func:`run_length.encode` compresses an iterable with run-length encoding.
It yields groups of repeated items with the count of how many times they
were repeated:
>>> uncompressed = 'abbcccdddd'
>>> list(run_length.encode(uncompressed))
[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
:func:`run_length.decode` decompresses an iterable that was previously
compressed with run-length encoding. It yields the items of the
decompressed iterable:
>>> compressed = [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
>>> list(run_length.decode(compressed))
['a', 'b', 'b', 'c', 'c', 'c', 'd', 'd', 'd', 'd']
"""
return
return
"""Return ``True`` if exactly ``n`` items in the iterable are ``True``
according to the *predicate* function.
>>> exactly_n([True, True, False], 2)
True
>>> exactly_n([True, True, False], 1)
False
>>> exactly_n([0, 1, 2, 3, 4, 5], 3, lambda x: x < 3)
True
The iterable will be advanced until ``n + 1`` truthy items are encountered,
so avoid calling it on infinite iterables.
"""
return ==
"""Return a list of circular shifts of *iterable*.
>>> circular_shifts(range(4))
[(0, 1, 2, 3), (1, 2, 3, 0), (2, 3, 0, 1), (3, 0, 1, 2)]
"""
=
return
"""Return a decorator version of *wrapping_func*, which is a function that
modifies an iterable. *result_index* is the position in that function's
signature where the iterable goes.
This lets you use itertools on the "production end," i.e. at function
definition. This can augment what the function returns without changing the
function's code.
For example, to produce a decorator version of :func:`chunked`:
>>> from more_itertools import chunked
>>> chunker = make_decorator(chunked, result_index=0)
>>> @chunker(3)
... def iter_range(n):
... return iter(range(n))
...
>>> list(iter_range(9))
[[0, 1, 2], [3, 4, 5], [6, 7, 8]]
To only allow truthy items to be returned:
>>> truth_serum = make_decorator(filter, result_index=1)
>>> @truth_serum(bool)
... def boolean_test():
... return [0, 1, '', ' ', False, True]
...
>>> list(boolean_test())
[1, ' ', True]
The :func:`peekable` and :func:`seekable` wrappers make for practical
decorators:
>>> from more_itertools import peekable
>>> peekable_function = make_decorator(peekable)
>>> @peekable_function()
... def str_range(*args):
... return (str(x) for x in range(*args))
...
>>> it = str_range(1, 20, 2)
>>> next(it), next(it), next(it)
('1', '3', '5')
>>> it.peek()
'7'
>>> next(it)
'7'
"""
# See https://sites.google.com/site/bbayles/index/decorator_factory for
# notes on how this works.
=
=
return
return
return
return
"""Return a dictionary that maps the items in *iterable* to categories
defined by *keyfunc*, transforms them with *valuefunc*, and
then summarizes them by category with *reducefunc*.
*valuefunc* defaults to the identity function if it is unspecified.
If *reducefunc* is unspecified, no summarization takes place:
>>> keyfunc = lambda x: x.upper()
>>> result = map_reduce('abbccc', keyfunc)
>>> sorted(result.items())
[('A', ['a']), ('B', ['b', 'b']), ('C', ['c', 'c', 'c'])]
Specifying *valuefunc* transforms the categorized items:
>>> keyfunc = lambda x: x.upper()
>>> valuefunc = lambda x: 1
>>> result = map_reduce('abbccc', keyfunc, valuefunc)
>>> sorted(result.items())
[('A', [1]), ('B', [1, 1]), ('C', [1, 1, 1])]
Specifying *reducefunc* summarizes the categorized items:
>>> keyfunc = lambda x: x.upper()
>>> valuefunc = lambda x: 1
>>> reducefunc = sum
>>> result = map_reduce('abbccc', keyfunc, valuefunc, reducefunc)
>>> sorted(result.items())
[('A', 1), ('B', 2), ('C', 3)]
You may want to filter the input iterable before applying the map/reduce
procedure:
>>> all_items = range(30)
>>> items = [x for x in all_items if 10 <= x <= 20] # Filter
>>> keyfunc = lambda x: x % 2 # Evens map to 0; odds to 1
>>> categories = map_reduce(items, keyfunc=keyfunc)
>>> sorted(categories.items())
[(0, [10, 12, 14, 16, 18, 20]), (1, [11, 13, 15, 17, 19])]
>>> summaries = map_reduce(items, keyfunc=keyfunc, reducefunc=sum)
>>> sorted(summaries.items())
[(0, 90), (1, 75)]
Note that all items in the iterable are gathered into a list before the
summarization step, which may require significant storage.
The returned object is a :obj:`collections.defaultdict` with the
``default_factory`` set to ``None``, such that it behaves like a normal
dictionary.
"""
=
=
=
=
=
= None
return
"""Yield the index of each item in *iterable* for which *pred* returns
``True``, starting from the right and moving left.
*pred* defaults to :func:`bool`, which will select truthy items:
>>> list(rlocate([0, 1, 1, 0, 1, 0, 0])) # Truthy at 1, 2, and 4
[4, 2, 1]
Set *pred* to a custom function to, e.g., find the indexes for a particular
item:
>>> iterable = iter('abcb')
>>> pred = lambda x: x == 'b'
>>> list(rlocate(iterable, pred))
[3, 1]
If *window_size* is given, then the *pred* function will be called with
that many items. This enables searching for sub-sequences:
>>> iterable = [0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3]
>>> pred = lambda *args: args == (1, 2, 3)
>>> list(rlocate(iterable, pred=pred, window_size=3))
[9, 5, 1]
Beware, this function won't return anything for infinite iterables.
If *iterable* is reversible, ``rlocate`` will reverse it and search from
the right. Otherwise, it will search from the left and return the results
in reverse order.
See :func:`locate` to for other example applications.
"""
=
return
pass
return
"""Yield the items from *iterable*, replacing the items for which *pred*
returns ``True`` with the items from the iterable *substitutes*.
>>> iterable = [1, 1, 0, 1, 1, 0, 1, 1]
>>> pred = lambda x: x == 0
>>> substitutes = (2, 3)
>>> list(replace(iterable, pred, substitutes))
[1, 1, 2, 3, 1, 1, 2, 3, 1, 1]
If *count* is given, the number of replacements will be limited:
>>> iterable = [1, 1, 0, 1, 1, 0, 1, 1, 0]
>>> pred = lambda x: x == 0
>>> substitutes = [None]
>>> list(replace(iterable, pred, substitutes, count=2))
[1, 1, None, 1, 1, None, 1, 1, 0]
Use *window_size* to control the number of items passed as arguments to
*pred*. This allows for locating and replacing subsequences.
>>> iterable = [0, 1, 2, 5, 0, 1, 2, 5]
>>> window_size = 3
>>> pred = lambda *args: args == (0, 1, 2) # 3 items passed to pred
>>> substitutes = [3, 4] # Splice in these items
>>> list(replace(iterable, pred, substitutes, window_size=window_size))
[3, 4, 5, 3, 4, 5]
"""
# Save the substitutes iterable, since it's used more than once
=
# Add padding such that the number of windows matches the length of the
# iterable
=
=
= 0
# If the current window matches our predicate (and we haven't hit
# our maximum number of replacements), splice in the substitutes
# and then consume the following windows that overlap with this one.
# For example, if the iterable is (0, 1, 2, 3, 4...)
# and the window size is 2, we have (0, 1), (1, 2), (2, 3)...
# If the predicate matches on (0, 1), we need to zap (0, 1) and (1, 2)
+= 1
yield from
continue
# If there was no match (or we've reached the replacement limit),
# yield the first item from the window.
yield
"""Yield all possible order-preserving partitions of *iterable*.
>>> iterable = 'abc'
>>> for part in partitions(iterable):
... print([''.join(p) for p in part])
['abc']
['a', 'bc']
['ab', 'c']
['a', 'b', 'c']
This is unrelated to :func:`partition`.
"""
=
=
yield
"""
Yield the set partitions of *iterable* into *k* parts. Set partitions are
not order-preserving.
>>> iterable = 'abc'
>>> for part in set_partitions(iterable, 2):
... print([''.join(p) for p in part])
['a', 'bc']
['ab', 'c']
['b', 'ac']
If *k* is not given, every set partition is generated.
>>> iterable = 'abc'
>>> for part in set_partitions(iterable):
... print([''.join(p) for p in part])
['abc']
['a', 'bc']
['ab', 'c']
['b', 'ac']
['a', 'b', 'c']
"""
=
=
> :
return
=
yield
== :
yield
, * =
yield
yield + +
yield from
yield from
"""
Yield items from *iterable* until *limit_seconds* have passed.
If the time limit expires before all items have been yielded, the
``timed_out`` parameter will be set to ``True``.
>>> from time import sleep
>>> def generator():
... yield 1
... yield 2
... sleep(0.2)
... yield 3
>>> iterable = time_limited(0.1, generator())
>>> list(iterable)
[1, 2]
>>> iterable.timed_out
True
Note that the time is checked before each item is yielded, and iteration
stops if the time elapsed is greater than *limit_seconds*. If your time
limit is 1 second, but it takes 2 seconds to generate the first item from
the iterable, the function will run for 2 seconds and not yield anything.
"""
=
=
=
= False
return
=
= True
return
"""If *iterable* has only one item, return it.
If it has zero items, return *default*.
If it has more than one item, raise the exception given by *too_long*,
which is ``ValueError`` by default.
>>> only([], default='missing')
'missing'
>>> only([1])
1
>>> only([1, 2]) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
ValueError: Expected exactly one item in iterable, but got 1, 2,
and perhaps more.'
>>> only([1, 2], too_long=TypeError) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
TypeError
Note that :func:`only` attempts to advance *iterable* twice to ensure there
is only one item. See :func:`spy` or :func:`peekable` to check
iterable contents less destructively.
"""
=
=
=
pass
=
return
"""Break *iterable* into sub-iterables with *n* elements each.
:func:`ichunked` is like :func:`chunked`, but it yields iterables
instead of lists.
If the sub-iterables are read in order, the elements of *iterable*
won't be stored in memory.
If they are read out of order, :func:`itertools.tee` is used to cache
elements as necessary.
>>> from itertools import count
>>> all_chunks = ichunked(count(), 4)
>>> c_1, c_2, c_3 = next(all_chunks), next(all_chunks), next(all_chunks)
>>> list(c_2) # c_1's elements have been cached; c_3's haven't been
[4, 5, 6, 7]
>>> list(c_1)
[0, 1, 2, 3]
>>> list(c_3)
[8, 9, 10, 11]
"""
=
# Check to see whether we're at the end of the source iterable
=
return
# Clone the source and yield an n-length slice
, =
yield
# Advance the source iterable
"""Yield the distinct combinations of *r* items taken from *iterable*.
>>> list(distinct_combinations([0, 0, 1], 2))
[(0, 0), (0, 1)]
Equivalent to ``set(combinations(iterable))``, except duplicates are not
generated and thrown away. For larger input sequences this is much more
efficient.
"""
== 0:
yield
return
=
=
= *
= 0
, =
-= 1
continue
=
yield
+= 1
"""Yield the items from *iterable* for which the *validator* function does
not raise one of the specified *exceptions*.
*validator* is called for each item in *iterable*.
It should be a function that accepts one argument and raises an exception
if that item is not valid.
>>> iterable = ['1', '2', 'three', '4', None]
>>> list(filter_except(int, iterable, ValueError, TypeError))
['1', '2', '4']
If an exception other than one given by *exceptions* is raised by
*validator*, it is raised like normal.
"""
pass
yield
"""Transform each item from *iterable* with *function* and yield the
result, unless *function* raises one of the specified *exceptions*.
*function* is called to transform each item in *iterable*.
It should be a accept one argument.
>>> iterable = ['1', '2', 'three', '4', None]
>>> list(map_except(int, iterable, ValueError, TypeError))
[1, 2, 4]
If an exception other than one given by *exceptions* is raised by
*function*, it is raised like normal.
"""
yield
pass
# Implementation of "Algorithm L" from the 1994 paper by Kim-Hung Li:
# "Reservoir-Sampling Algorithms of Time Complexity O(n(1+log(N/n)))".
# Fill up the reservoir (collection of samples) with the first `k` samples
=
# Generate random number that's the largest in a sample of k U(0,1) numbers
# Largest order statistic: https://en.wikipedia.org/wiki/Order_statistic
=
# The number of elements to skip before changing the reservoir is a random
# number with a geometric distribution. Sample it using random() and logs.
= +
=
# The new W is the largest in a sample of k U(0, `old_W`) numbers
*=
+= + 1
return
# Implementation of "A-ExpJ" from the 2006 paper by Efraimidis et al. :
# "Weighted random sampling with a reservoir".
# Log-transform for numerical stability for weights that are small/large
=
# Fill up the reservoir (collection of samples) with the first `k`
# weight-keys and elements, then heapify the list.
=
# The number of jumps before changing the reservoir is a random variable
# with an exponential distribution. Sample it using random() and logs.
, =
= /
# The notation here is consistent with the paper, but we store
# the weight-keys in log-space for better numerical stability.
, =
=
= # generate U(t_w, 1)
= /
, =
= /
-=
# Equivalent to [element for weight_key, element in sorted(reservoir)]
return
"""Return a *k*-length list of elements chosen (without replacement)
from the *iterable*. Like :func:`random.sample`, but works on iterables
of unknown length.
>>> iterable = range(100)
>>> sample(iterable, 5) # doctest: +SKIP
[81, 60, 96, 16, 4]
An iterable with *weights* may also be given:
>>> iterable = range(100)
>>> weights = (i * i + 1 for i in range(100))
>>> sampled = sample(iterable, 5, weights=weights) # doctest: +SKIP
[79, 67, 74, 66, 78]
The algorithm can also be used to generate weighted random permutations.
The relative weight of each item determines the probability that it
appears late in the permutation.
>>> data = "abcdefgh"
>>> weights = range(1, len(data) + 1)
>>> sample(data, k=len(data), weights=weights) # doctest: +SKIP
['c', 'a', 'b', 'e', 'g', 'd', 'h', 'f']
"""
return
=
return
=
return
"""Returns ``True`` if the items of iterable are in sorted order, and
``False`` otherwise. *key* and *reverse* have the same meaning that they do
in the built-in :func:`sorted` function.
>>> is_sorted(['1', '2', '3', '4', '5'], key=int)
True
>>> is_sorted([5, 4, 3, 1, 2], reverse=True)
False
The function returns ``False`` after encountering the first out-of-order
item. If there are no out-of-order items, the iterable is exhausted.
"""
=
=
return not
pass
"""Convert a function that uses callbacks to an iterator.
Let *func* be a function that takes a `callback` keyword argument.
For example:
>>> def func(callback=None):
... for i, c in [(1, 'a'), (2, 'b'), (3, 'c')]:
... if callback:
... callback(i, c)
... return 4
Use ``with callback_iter(func)`` to get an iterator over the parameters
that are delivered to the callback.
>>> with callback_iter(func) as it:
... for args, kwargs in it:
... print(args)
(1, 'a')
(2, 'b')
(3, 'c')
The function will be called in a background thread. The ``done`` property
indicates whether it has completed execution.
>>> it.done
True
If it completes successfully, its return value will be available
in the ``result`` property.
>>> it.result
4
Notes:
* If the function uses some keyword argument besides ``callback``, supply
*callback_kwd*.
* If it finished executing, but raised an exception, accessing the
``result`` property will raise the same exception.
* If it hasn't finished executing, accessing the ``result``
property from within the ``with`` block will raise ``RuntimeError``.
* If it hasn't finished executing, accessing the ``result`` property from
outside the ``with`` block will raise a
``more_itertools.AbortThread`` exception.
* Provide *wait_seconds* to adjust how frequently the it is polled for
output.
"""
=
=
= False
= None
=
=
=
return
= True
return
return
return False
return
return
=
=
=
pass
yield
break
=
=
break
yield from
"""
Yield ``(beginning, middle, end)`` tuples, where:
* Each ``middle`` has *n* items from *iterable*
* Each ``beginning`` has the items before the ones in ``middle``
* Each ``end`` has the items after the ones in ``middle``
>>> iterable = range(7)
>>> n = 3
>>> for beginning, middle, end in windowed_complete(iterable, n):
... print(beginning, middle, end)
() (0, 1, 2) (3, 4, 5, 6)
(0,) (1, 2, 3) (4, 5, 6)
(0, 1) (2, 3, 4) (5, 6)
(0, 1, 2) (3, 4, 5) (6,)
(0, 1, 2, 3) (4, 5, 6) ()
Note that *n* must be at least 0 and most equal to the length of
*iterable*.
This function will exhaust the iterable and may require significant
storage.
"""
=
=
=
=
=
yield , ,
"""
Returns ``True`` if all the elements of *iterable* are unique (no two
elements are equal).
>>> all_unique('ABCB')
False
If a *key* function is specified, it will be used to make comparisons.
>>> all_unique('ABCb')
True
>>> all_unique('ABCb', str.lower)
False
The function returns as soon as the first non-unique element is
encountered. Iterables with a mix of hashable and unhashable items can
be used, but the function will be slower for unhashable items.
"""
=
=
=
=
return False
return False
return True
"""Equivalent to ``list(product(*args))[index]``.
The products of *args* can be ordered lexicographically.
:func:`nth_product` computes the product at sort position *index* without
computing the previous products.
>>> nth_product(8, range(2), range(2), range(2), range(2))
(1, 0, 0, 0)
``IndexError`` will be raised if the given *index* is invalid.
"""
=
=
=
+=
=
//=
return
"""Equivalent to ``list(permutations(iterable, r))[index]```
The subsequences of *iterable* that are of length *r* where order is
important can be ordered lexicographically. :func:`nth_permutation`
computes the subsequence at sort position *index* directly, without
computing the previous subsequences.
>>> nth_permutation('ghijk', 2, 5)
('h', 'i')
``ValueError`` will be raised If *r* is negative or greater than the length
of *iterable*.
``IndexError`` will be raised if the given *index* is invalid.
"""
=
=
, = ,
not 0 <= < :
= //
+=
return
= *
= * //
, =
=
break
return
"""Yield all arguments passed to the function in the same order in which
they were passed. If an argument itself is iterable then iterate over its
values.
>>> list(value_chain(1, 2, 3, [4, 5, 6]))
[1, 2, 3, 4, 5, 6]
Binary and text strings are not considered iterable and are emitted
as-is:
>>> list(value_chain('12', '34', ['56', '78']))
['12', '34', '56', '78']
Multiple levels of nesting are not flattened.
"""
yield
continue
yield from
yield
"""Equivalent to ``list(product(*args)).index(element)``
The products of *args* can be ordered lexicographically.
:func:`product_index` computes the first index of *element* without
computing the previous products.
>>> product_index([8, 2], range(10), range(5))
42
``ValueError`` will be raised if the given *element* isn't in the product
of *args*.
"""
= 0
=
= * +
return
"""Equivalent to ``list(combinations(iterable, r)).index(element)``
The subsequences of *iterable* that are of length *r* can be ordered
lexicographically. :func:`combination_index` computes the index of the
first *element*, without computing the previous combinations.
>>> combination_index('adf', 'abcdefg')
10
``ValueError`` will be raised if the given *element* isn't one of the
combinations of *iterable*.
"""
=
, =
return 0
=
=
, =
break
=
, =
# Python versiosn below 3.8 don't have math.comb
= 1
= -
+= //
return // -
"""Equivalent to ``list(permutations(iterable, r)).index(element)```
The subsequences of *iterable* that are of length *r* where order is
important can be ordered lexicographically. :func:`permutation_index`
computes the index of the first *element* directly, without computing
the previous permutations.
>>> permutation_index([1, 3, 2], range(5))
19
``ValueError`` will be raised if the given *element* isn't one of the
permutations of *iterable*.
"""
= 0
=
=
= * +
del
return
"""Wrap *iterable* and keep a count of how many items have been consumed.
The ``items_seen`` attribute starts at ``0`` and increments as the iterable
is consumed:
>>> iterable = map(str, range(10))
>>> it = countable(iterable)
>>> it.items_seen
0
>>> next(it), next(it)
('0', '1')
>>> list(it)
['2', '3', '4', '5', '6', '7', '8', '9']
>>> it.items_seen
10
"""
=
= 0
return
=
+= 1
return