Python: Nested Loop

Question

Consider this:

>>> a = [("one","two"), ("bad","good")]

>>> for i in a:
...     for x in i:
...         print x
... 
one
two
bad
good

How can I write this code, but using a syntax like:

for i in a:
    print [x for x in i]

Obviously, This does not work, it prints:

['one', 'two']
['bad', 'good']

I want the same output. Can it be done?

Answer 1

List comprehensions and generators are only designed to be used as expressions, while printing is a statement. While you can effect what you're trying to do by doing

from __future__ import print_function
for x in a:
    [print(each) for each in x]

doing so is amazingly unpythonic, and results in the generation of a list that you don't actually need. The best thing you could do would simply be to write the nested for loops in your original example.

Answer 2

Given your example you could do something like this:

a = [("one","two"), ("bad","good")]

for x in sum(map(list, a), []):
    print x

This can, however, become quite slow once the list gets big.

The better way to do it would be like Tim Pietzcker suggested:

from itertools import chain

for x in chain(*a):
    print x

Using the star notation, *a, allows you to have n tuples in your list.