Truthiness and falsiness

Truthy and falsey

Python allows many shortcuts with Boolean expressions. Most everything in Python has a truth value. As noted earlier, we refer to the truth values of anything other than Booleans with the whimsical terms “truthy” and “falsey” (we also use the terms “truthiness” and “falsiness”).

When used in Boolean expressions and conditions for loops or branching (if/elif), truthy values are treated (more-or-less) as True, and falsey values are treated (more-or-less) as False.

Truthy things	Falsey things
any non-zero valued int or float,	0, 0.0
5, -17, 3.1415
any non-empty list,	the empty list, []
['foo'], [0], ['a', 'b', 'c']
any non-empty tuple,	the empty tuple, ()
(42.781, -73.901), ('vladimir')
any non-empty string,	the empty string, ""
"bluster", "kimchee"

This allows us to use conditions such as these:

if x % 2:
    # it's odd
    print(f"{x} is odd")

if not s:
   print("The string, s, is empty!")

If you want to know if something is truthy or falsey in Python, you can pass the value or expression to the Boolean constructor, bool().

>>> bool(1)
True
>>> bool(-1)
True
>>> bool(0)
False
>>> bool('xyz')
True
>>> bool('')
False
>>> bool(None)
False

Original author: Clayton Cafiero < [given name] DOT [surname] AT uvm DOT edu >

No generative AI was used in producing this material. This was written the old-fashioned way.

This material is for free use under either the GNU Free Documentation License or the Creative Commons Attribution-ShareAlike 3.0 United States License (take your pick).