The itertools of the Python standard library

Itertools Library

Iterators (generators) are a very common and useful data structure in Python, and the biggest advantage of iterators over lists (list) is that they are deferred and used on demand.

Several methods of Itertools library are introduced:

itertools.accumulate: List Accumulation method

>>> import itertools>>> x = itertools.accumulate (range) >>> print (list (x)) [0, 1, 3, 6, 10, 15, 21, 28, 36, 45]

Itertools.chain: How to synthesize multiple lists into a list

>>> x = [1,2,3]>>> y = [4,5,6]>>> a = Itertools.chain (x, y) >>> print (list (a)) [1, 2, 3, 4, 5, 6]

itertools.combinations: All combinations of the specified number of elements in the list are not duplicated

Note: 2 means to find a random set of 2 elements in a list with no duplicates

>>> x = [1,2,3,4,5]>>> a = itertools.combinations (x,2) >>> print (list (a)) [(1, 2), (1, 3), (1, 4) , (1, 5), (2, 3), (2, 4), (2, 5), (3, 4), (3, 5), (4, 5)]

Itertools.islice: Slicing a list

Note: 0 indicates the starting position, 5 means the end position, and 2 indicates the step

>>> x = [1,2,3,4,5]>>> a = Itertools.islice (x,0,5,2) >>> print (list (a)) [1, 3, 5]

itertools.count: Counter, can specify start position and step size

Note: Start indicates the starting position, step is the step

>>> x = Itertools.count (start=2,step=3) >>> print (List (Itertools.islice (x,5))) [2, 5, 8, 11, 14]

itertools.cycle: Data in a loop list or iterator

>>> x = itertools.cycle (' ABCD ') >>> print (List (Itertools.islice (x,0,10,2))) [' A ', ' C ', ' A ', ' C ', ' a ']

itertools.repeat: Generates an iterator with the specified number of elements and the same element

>>> Print (List (itertools.repeat (' Liuwei ', 5))) [' Liuwei ', ' Liuwei ', ' Liuwei ', ' Liuwei ', ' Liuwei ']# You can also use the following method to generate a list of the same elements >>> item = ["Liu"]*5>>> print (item) [' Liu ', ' Liu ', ' Liu ', ' Liu ', ' Liu ']

There's a lot more to be done.

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The itertools of the Python standard library