and / or operators return value [duplicate]

The and and or operators do return one of their operands, not a pure boolean value like True or False:

>>> 0 or 42
42
>>> 0 and 42
0

Whereas not always returns a pure boolean value:

>>> not 0
True
>>> not 42
False

See this table from the standard library reference in the Python docs:

from Python docs:

The operator not yields True if its argument is false, False otherwise.

The expression x and y first evaluates x; if x is false, its value is returned; otherwise, y is evaluated and the resulting value is returned.

The expression x or y first evaluates x; if x is true, its value is returned; otherwise, y is evaluated and the resulting value is returned.

Python's or operator returns the first Truth-y value, or the last value, and stops. This is very useful for common programming assignments that need fallback values.

Like this simple one:

print my_list or "no values"

This will print my_list, if it has anything in it. Otherwise, it will print no values (if list is empty, or it is None...).

A simple example:

>>> my_list = []
>>> print my_list or 'no values'
no values
>>> my_list.append(1)
>>> print my_list or 'no values'
[1]

The compliment by using and, which returns the first False-y value, or the last value, and stops, is used when you want a guard rather than a fallback.

Like this one:

my_list and my_list.pop()

This is useful since you can't use list.pop on None, or [], which are common prior values to lists.

A simple example:

>>> my_list = None
>>> print my_list and my_list.pop()
None
>>> my_list = [1]
>>> print my_list and my_list.pop()
1

In both cases non-boolean values were returned and no exceptions were raised.