8.11) The True Nature Of Objects

In Python, all objects, whatever their type have inherent True or False properties.

The following values are considered false:

None

False

zero of any numeric type (integer, float or complex), for example, 0, 0.0, 0j

any empty sequence (e.g. string, list or tuple), for example, "", (), []

any empty mapping (i.e. dictionary), for example, {}

All other values are considered true, so most values are true in Python.

So checking whether a Dictionary or sequence is empty or whether a value is None is really straightforward. For example, this will only print the first element of a list if the list is not empty otherwise, it prints 'empty list':

>>> L=[] # initialise empty list
>>> if L:
        print L[0]
    else:
        print 'empty list'
empty list

First Page

Last Page