Why Does List.append Evaluate To False In A Boolean Context?

Is there a reason being list.append evaluating to false? Or is it just the C convention of returning 0 when successful that comes into play? >>> u = [] >>> not u.

Solution 1:

Most Python methods that mutate a container in-place return None -- an application of the principle of Command-query separation. (Python's always reasonably pragmatic about things, so a few mutators do return a usable value when getting it otherwise would be expensive or a mess -- the pop method is a good example of this pragmatism -- but those are definitely the exception, not the rule, and there's no reason to make append an exception).

Solution 2:

None evaluates to False and in python a function that does not return anything is assumed to have returned None.

If you type:

>> print u.append(6)
None

Tadaaam :)

Solution 3:

because .append method returns None, therefore not None evaluates to True. Python on error usually raises an error:

>>> a = ()
>>> a.append(5)
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    a.append(5)
AttributeError: 'tuple'object has no attribute 'append'

Solution 4:

It modifies the list in-place, and returns None. None evaluates to false.

Solution 5:

Actually, it returns None

>>>print u.append(6)
None
>>>printnotNone
True
>>>