Beginner question...

Why does this happen? Why doesn't the reverse function work when given with list but does work with the variable?

>>> a=[1,2].reverse()
>>> a      <--- a is None
>>> a=[1,2]
>>> a.reverse()
>>> a      <--- a is not None and doing what I wanted him to do
[2, 1]
>>>  

CodePudding user response：

It does work. The list reverse method in Python doesn't return reversed list (it doesn't return anything == returns None), it reverses the list it's applied to in place. When you call it on a list literal it is in fact reversed, but there is no way to get the reversed list.

There is reversed function (https://docs.python.org/3/library/functions.html#reversed) that does what you expect

CodePudding user response：

1. reverse() doesnt return any value,i.e, it returns None.
2. Reverse() modifies the list in place.

In your first case, you are inturn setting a = None.

In your second case, a is modified by reverse(), and you are able to print the modified "a".

CodePudding user response：

That is because reverse() returns None, but it reverses the order of items in the list.

For example,

>>>a = [1, 2].reverse() # It reversed [1, 2] to [2, 1] but returns None. 
>>>a # The reversed value of [2, 1] disappears, 
# And returned value of None has been assigned to variable a
None

>>>a=[1,2] 
>>>a.reverse() # The order of items of a has been reversed and return None, 
# but there is no variable to take returned value, None.
>>> a
[2, 1]