singledispatch in Python

One function name, an implementation chosen by the first argument's type.

from functools import singledispatch


@singledispatch
def summarize(value):
    return f"{type(value).__name__}: {value!r}"


@summarize.register
def _(value: int):
    return f"int: {value:+d}"


@summarize.register
def _(value: list):
    return f"list of {len(value)}"


@summarize.register(str)
def _(value):
    return f"text of {len(value)} chars"


for item in (3, "hello", [1, 2], 2.5):
    print(summarize(item))

How it works

1. @singledispatch defines the fallback.
2. @name.register adds a typed implementation.
3. It replaces a chain of isinstance checks.

Keywords and builtins used here

• _
• def
• for
• int
• len
• list
• print
• return
• str
• summarize
• type

The run, in numbers

Lines

25

Characters to type

402

Tokens

120

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 69 seconds.

Type this snippet

Step 2 of 3 in functools & operator, step 39 of 53 in Pythonic Python.

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