Violation of PEP8 programming recommendations
Following PEP8 makes your code clear and more readable. Often there are several ways to perform a similar action in Python. PEP 8 provides recommendations to remove that ambiguity and preserve consistency.
def readable_noncompliant():
    # Noncompliant: violates PEP8 programming recommendations,
    # making it difficult to read.
    if not a is None:
        print(a)
def readable_compliant():
    # Compliant: follows the PEP8 programming recommendations,
    # improving readability.
    if a is not None:
        print(a)