truthvalues.md

Truth values for conditions [Readbility, Programming Efficiency]

The following are part of the PEP 8 Python Style Guide, which gives some guidelines on the preferred way to write conditions for if statements.

Comparing things to True

Not pythonic

something = True

if something == True:
    pass

if something is True:
    pass

Pythonic

if something:
    print("This is good!")

## for False:
something = False
if not something:
    print("Yay!")

Comparing things to None

something = None

if something == None:
    pass

# Also bad
if not something is None:
    pass

Pythonic

if something is None:
    print("This is good!")

if something is not None:
    print("Yay!")

Checking for empty sequences (i.e strings, lists, tuples)

Not pythonic

some_list = []

if len(some_list) == 0:
    pass

if not len(some_list):
    pass

Pythonic

if some_list:
    print("This is good!")

if not some_list:
    print("Yay!")

Unnecessary ors

Unpythonic

something = "Hello"
if something == "Hello" or something == "Hi" or something = "Hey":
    print("This is pretty noisy!")

greetings = ["Hello", "Hi", "Hey"]
if something in greetings:
    print("Better!")

value = 3
if value in [1, 2, 3, 4, 5]:
    print("Good too!")

---

References

[1] PEP 8 -- Style Guide for Python Code

Books that mention this topic:

[2] Python Tricks: A Buffet of Awesome Python Features by Dan Bader
[3] Effective Python: 90 Specific Ways to Write Better Python by Brett Slatkin
[4] Python Cookbook, Third Edition by David Beazley and Brian K. Jones
[5] Writing Idiomatic Python 3 by Jeff Knupp
[6] The Little Book of Python Anti-Patterns by QuantifiedCode