How to Write Pythonic Loops: Conclusion

Thanks. As an Old C Guy, this was very informative. It will probably take a bit of work to overcome my bad habits.

loved this course, very informative.

Quite enlighten.

Being Pythonic… nice message, interesting content.

Very interesting tutorial; thanks Dan!

nice, clear, thanks alot )

Thanks for the info!

This may well be covered elsewhere but I’d like to know if nested loops are treated the same? Do they HAVE to be across two lines, or is there a magic one-liner method?

I tried:

my_list = ['a', 'b', 'c']
my_num = [1, 2, 3]

for (item, num) in (my_list, my_num):
    print(item, num)

and found ValueError: too many values to unpack (expected 2)

whereas:

for items in my_items:
    for num in my_num:
        print(items, num)

Yielded the expected result, anyone able to shed some light on this one? Cheers (:

Hi @JeremyMechEng

Python doesn’t have dedicated syntax for nested for loops. However, you can use itertools.product() to nest your lists and then loop over that product:

import itertools

characters = ["a", "b", "c"]
digits = [1, 2, 3]

for char, digit in itertools.product(characters, digits):
    print(char, digit)

realpython.com/python-itertools/#dealing-a-deck-of-cards shows another example of using itertools.product().

@JeremyMechEng or you could use a list comprehension:

>>> characters = ["a", "b", "c"]
>>> digits = [1, 2, 3]
>>> [print(c, d) for c in characters for d in digits]
a 1
a 2
a 3
b 1
b 2
b 3
c 1
c 2
c 3
[None, None, None, None, None, None, None, None, None]

Note that in this case it’ll create a list with the return value of calling print(), which is None. So it’ll be more interesting if you want to build a list.

Also, complex list comprehensions get messy and hard to understand quickly, so it’s rarely worth it to go into the level of nested loops. It’ll be more readable to write out the nested for loop instead.

@Geir Arne Hjelle @Martin Breuss Thanks both for the answers! Much appreciated