Python : Calling functions from inside another function parameter

Question

I'm new to python so please excuse the layman description.

Question : Given a sentence, return a sentence with the words reversed

My Solution:

def sentence_reverse(text):
    a = text.split()
    a.reverse()
    return ' '.join(a)

Output:

sentence_reverse('I am home') --> 'home am I'
sentence_reverse('We are ready') --> 'ready are We'

the code works the way it is supposed to but my question is, why can't i make a function call directly from the returned result of the previous function. i,e

why can i not do something like

return ' '.join(text.split().reverse())

this would work just fine in java since i get List object from text.split() to which, i would operate on with the reverse() function which would return me the inverted list which would then be used by the join() to make this list into a string.

This, is also something that i have tried:

text.split() returns a List, and applying .reverse() function on it SHOULD return the elements of the same list in reverse order, but when i execute this line, print(text.split().reverse()) , i get None

Answer 1

Because reverse returns None, and updates the list, so so None is not valid for join .

Yeah so reverse is inplace function so no way to fix that.

So Use reversed :

return ' '.join(reversed(text.split()))

Or [::-1] :

return ' '.join(text.split()[::-1])

From docs:

You might have noticed that methods like insert, remove or sort that only modify the list have no return value printed – they return the default None. [1] This is a design principle for all mutable data structures in Python.

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After code example.

https://docs.python.org/3/tutorial/datastructures.html

Answer 2

which would return me the inverted list ..

Here's the problem. In Python, calling list.reverse() doesn't return the reversed list. It just reverses it in place.

What you need is:

return " ".join(text.split()[::-1])

Answer 3

Instead of using .reverse You can use python list iterator to reverse:

me = 'ready are We'
" ".join(me.split()[::-1])
>>> 'We are ready'