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from sys import version_info
from collections import deque, Iterable
from operator import add, itemgetter, attrgetter, not_
from functools import partial
from itertools import (islice,
chain,
starmap,
repeat,
tee,
cycle,
takewhile,
dropwhile,
combinations)
from .op import flip
from .func import F
from .uniform import *
def take(limit, base):
return islice(base, limit)
def drop(limit, base):
return islice(base, limit, None)
def takelast(n, iterable):
"Return iterator to produce last n items from origin"
return iter(deque(iterable, maxlen=n))
def droplast(n, iterable):
"Return iterator to produce items from origin except last n"
t1, t2 = tee(iterable)
return map(itemgetter(0), zip(t1, islice(t2, n, None)))
def consume(iterator, n=None):
"""Advance the iterator n-steps ahead. If n is none, consume entirely.
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
# Use functions that consume iterators at C speed.
if n is None:
# feed the entire iterator into a zero-length deque
deque(iterator, maxlen=0)
else:
# advance to the empty slice starting at position n
next(islice(iterator, n, n), None)
def nth(iterable, n, default=None):
"""Returns the nth item or a default value
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
return next(islice(iterable, n, None), default)
def first_true(iterable, default=False, pred=None):
"""Returns the first true value in the iterable.
If no true value is found, returns *default*
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
return next(filter(pred, iterable), default)
# widely-spreaded shortcuts to get first item, all but first item,
# second item, and first item of first item from iterator respectively
head = first = partial(flip(nth), 0)
tail = rest = partial(drop, 1)
second = F(rest) >> first
ffirst = F(first) >> first
# shortcut to remove all falsey items from iterable
compact = partial(filter, None)
# filterfalse under alias 'reject'
reject = filterfalse
# shortcuts to 1. return True if f(x) is logical true for every x in
# iterable (False otherwise), and 2. return the first logical true
# value of f(x) for any x in iterable (None otherwise) respectively
every = F(partial(map)) >> all
some = F(partial(map)) >> compact >> first
def iterate(f, x):
"""Return an iterator yielding x, f(x), f(f(x)) etc.
"""
while True:
yield x
x = f(x)
def padnone(iterable):
"""Returns the sequence elements and then returns None indefinitely.
Useful for emulating the behavior of the built-in map() function.
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
return chain(iterable, repeat(None))
def ncycles(iterable, n):
"""Returns the sequence elements n times
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
return chain.from_iterable(repeat(tuple(iterable), n))
def repeatfunc(func, times=None, *args):
"""Repeat calls to func with specified arguments.
Example: repeatfunc(random.random)
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
if times is None:
return starmap(func, repeat(args))
return starmap(func, repeat(args, times))
def grouper(n, iterable, fillvalue=None):
"""Collect data into fixed-length chunks or blocks, so
grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
args = [iter(iterable)] * n
return zip_longest(*args, fillvalue=fillvalue)
def group_by(keyfunc, iterable):
"""Returns a dict of the elements from given iterable keyed by result
of keyfunc on each element. The value at each key will be a list of
the corresponding elements, in the order they appeared in the iterable.
"""
grouped = {}
for item in iterable:
grouped.setdefault(keyfunc(item), []).append(item)
return grouped
def roundrobin(*iterables):
"""roundrobin('ABC', 'D', 'EF') --> A D E B F C
Recipe originally credited to George Sakkis.
Reimplemented to work both in Python 2+ and 3+.
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
pending = len(iterables)
next_attr = "next" if version_info[0] == 2 else "__next__"
nexts = cycle(map(attrgetter(next_attr), map(iter, iterables)))
while pending:
try:
for n in nexts:
yield n()
except StopIteration:
pending -= 1
nexts = cycle(islice(nexts, pending))
def partition(pred, iterable):
"""Use a predicate to partition entries into false entries and true entries
partition(is_odd, range(10)) --> 0 2 4 6 8 and 1 3 5 7 9
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
t1, t2 = tee(iterable)
return filterfalse(pred, t1), filter(pred, t2)
def splitat(t, iterable):
"""Split iterable into two iterators after given number of iterations
splitat(2, range(5)) --> 0 1 and 2 3 4
"""
t1, t2 = tee(iterable)
return islice(t1, t), islice(t2, t, None)
def splitby(pred, iterable):
"""Split iterable into two iterators at first false predicate
splitby(is_even, range(5)) --> 0 and 1 2 3 4
"""
t1, t2 = tee(iterable)
return takewhile(pred, t1), dropwhile(pred, t2)
def powerset(iterable):
"""powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
s = list(iterable)
return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
def pairwise(iterable):
"""pairwise(s) -> (s0,s1), (s1,s2), (s2, s3), ...
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
a, b = tee(iterable)
next(b, None)
return zip(a, b)
def iter_except(func, exception, first_=None):
""" Call a function repeatedly until an exception is raised.
Converts a call-until-exception interface to an iterator interface.
Like __builtin__.iter(func, sentinel) but uses an exception instead
of a sentinel to end the loop.
Examples:
iter_except(functools.partial(heappop, h), IndexError) # priority queue iterator
iter_except(d.popitem, KeyError) # non-blocking dict iterator
iter_except(d.popleft, IndexError) # non-blocking deque iterator
iter_except(q.get_nowait, Queue.Empty) # loop over a producer Queue
iter_except(s.pop, KeyError) # non-blocking set iterator
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
try:
if first_ is not None:
yield first_() # For database APIs needing an initial cast to db.first()
while 1:
yield func()
except exception:
pass
def flatten(items):
"""Flatten any level of nested iterables (not including strings, bytes or
bytearrays).
Reimplemented to work with all nested levels (not only one).
http://docs.python.org/3.4/library/itertools.html#itertools-recipes
"""
for item in items:
is_iterable = isinstance(item, Iterable)
is_string_or_bytes = isinstance(item, (str, bytes, bytearray))
if is_iterable and not is_string_or_bytes:
for i in flatten(item):
yield i
else:
yield item
if version_info[0] == 3 and version_info[1] >= 3:
from itertools import accumulate
else:
def accumulate(iterable, func=add):
"""Make an iterator that returns accumulated sums.
Elements may be any addable type including Decimal or Fraction.
If the optional func argument is supplied, it should be a
function of two arguments and it will be used instead of addition.
Origin implementation:
http://docs.python.org/dev/library/itertools.html#itertools.accumulate
Backported to work with all python versions (< 3.3)
"""
it = iter(iterable)
total = next(it)
yield total
for element in it:
total = func(total, element)
yield total
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