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Aug 15, 2022

#advanced-python

Avoiding nested loops

Without Itertools

for elem1 in list1: 	
    for elem2 in list2: 		
        process(elem1, elem2)

With Itertools

import itertools 
for elem1, elem2 in itertools.product(list1, list2): 	
    process(elem1, elem2)

And of course the itertools example, if it is as simple as a single function call, can be shortened to :

map(process, itertools.product(list1, list2) )

Also it can be extended to multiple lists, iterables etc, without needing to have another nested loop.

Infinite loop with a count

Without Itertools

iteration = 0 
while True: 	
    process( iteration ) 	
    iteration +=1

With Itertools

import itertools 
for iteration in itertools.count(): 	
    process( iteration)

no risk of ever stepping past the increment line by doing a continue for instance (been there, done that)

Running lists together

Without Itertools

for element in list1 + list2 + list3: 	
    process( element )

With Itertools

import itertools 
for element in itertools.chain( list1, list2, list3): 	
    process(element)

Itertools with list of list

import itertools 
for element in itertools.chain.from_iterable( list_of_lists ): 	
    process(element)

List with Condition

Without Itertools

for element in my_list:    
    if condition(element): 		
        break    
    process(element)

With Itertools

import itertools 
for element in itertools.takewhile(lambda x: not condition(x), my_list): 	
    process(element)

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