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.
