None and defaults in Python

Representing absence: the value that means nothing was found.

def find_user(users, name):
    for user in users:
        if user["name"] == name:
            return user
    return None


user = find_user([{"name": "sam"}], "alex")
if user is None:
    display = "guest"
else:
    display = user["name"]

nickname = None
shown = nickname or "anonymous"

How it works

1. A search that finds nothing returns None explicitly.
2. Checks identity with is None, never == None.
3. Falls back to a default with the or idiom.

Keywords and builtins used here

• def
• else
• find_user
• for
• if
• return

The run, in numbers

Lines

15

Characters to type

254

Tokens

77

Three-star pace

85 tpm

At the three-star pace of 85 tokens a minute, this run takes about 54 seconds.

Type this snippet

Step 5 of 6 in Variables & types, step 5 of 72 in Language basics.

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