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
.''
, ()
, []
.{}
.__nonzero__()
or __len__()
method, when that
method returns zero.
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' and
`and' always return one of their operands.)