How to use the itertools package of python

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Foreword:

Python's built-in module itertools provides very useful functions for manipulating iterative objects, and several "infinite" iterators provided by itertools

1. Count () creates a sequence of natural numbers import itertools n = 0natuals = itertools.count (1) for m in natuals: print (m)

Because count (n) creates an infinite iterator, starting with n, iterating to infinity. So the above code will print out a sequence of natural numbers, can not stop at all, can only press Ctrl+C to exit.

Running result:

0 1 2 3 4 5 6 7...

2. Cycle () creates a sequence loop

Cycle () repeats an incoming sequence indefinitely.

Example 1. The contents of the circular list:

Natuals = itertools.cycle ([1,2,3]) for m in natuals: print (m)

Running result:

1 2 3 1 2 3 1 2 3...

Example 2. Character loop in a string:

Import itertoolscs = itertools.cycle ('ABC') # Note that a string is also a for c in cs of a sequence: print (c)

Running result:

A B C A B C A B C...

3. Repeat () repeats an element a finite number of times

Repeat () is responsible for repeating an element indefinitely (the default behavior), but you can limit the number of repeats if you provide a second parameter.

Ns = itertools.repeat ('Aids, 3) for n in ns: print (n)

Running result:

An An A...

4. Takewhile () intercepts a finite sequence according to conditional judgment.

An infinite sequence iterates indefinitely only when for iterates. If you just create an iterative object, it does not generate infinite elements in advance, and in fact it is impossible to create unlimited elements in memory. Although the infinite sequence can be iterated indefinitely, we usually intercept a finite sequence according to the conditional judgment through functions such as takewhile ().

Import itertools natuals = itertools.count (1) ns = itertools.takewhile (lambda x: X