Any object can be tested for truth value, for use in an if or
while condition or as operand of the Boolean operations below.
The following values are considered false:
None
0, 0L,
0.0, 0j.
'', (), [].
{}.
All other values are considered true -- so objects of many types are
always true.
Operations and built-in functions that have a Boolean result always
return 0 for false and 1 for true, unless otherwise
stated. (Important exception: the Boolean operations
"or"