Check none

None (Null Value)

syntax

variable = None

example

result = None
if result is None:
    print("No result yet")

# Common pattern: optional return
def find_user(user_id: int) -> str | None:
    return None

output

No result yet

Note Always compare to None with 'is' or 'is not', never == or !=. None is a singleton object.

Truthiness Gotchas

PY · Common Mistakes

syntax

# Falsy: None, False, 0, 0.0, '', [], {}, set()

example

def process(data=None):
    # WRONG: if not data
    # This also catches empty list [], 0, and ""
    if not data:
        print("No data")  # Triggered by empty list too!

    # CORRECT: if data is None
    if data is None:
        print("Data is None")

process([])   # Might not intend to reject []
process(None)
process(0)

output

No data
No data
Data is None
No data

Note Empty collections, zero, empty string, and None are all falsy. When you specifically mean 'no value provided', check 'is None' rather than relying on truthiness.

PYPython