How to apply a function to each sublist of a list in python?

Question

Lets say I have a list like this:

list_of_lists = [[\'how to apply\'],[\'a function\'],[\'to each list?\']]

And I have a function let\'s sa

Answer 1

You can use a list comprehension, like this

[function_to_be_done(item) for item in list_of_lists]

For example,

>>> list_of_lists = [['how to apply'],['a function'],['to each list?']]
>>> [len(item) for item in list_of_lists]
[1, 1, 1]

Note: Though list comprehensions look like a way to apply a function to all the elements, its main purpose is to construct a new list. So, if you don't want to construct a new list, then just iterate with for loop and call the function.

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Apart from that, you can use the map function in Python 2.7, to apply a function to all the elements and construct a list. For example,

>>> list_of_lists = [['how to apply'],['a function'],['to each list?']]
>>> map(len, list_of_lists)
[1, 1, 1]

But, map returns a map iterator object in Python 3.x. So, you need to explicitly convert that to a list, like this

>>> list_of_lists = [['how to apply'],['a function'],['to each list?']]
>>> map(len, list_of_lists)

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You might want to read about, what Guido thinks about map in this post.

Basically, map would more often demand you to create a new function (mostly people create a lambda function). But in many cases, list comprehension avoids that.