TypedDict and NewType in Python

Typing the shape of a dict, and giving a primitive a distinct name.

from typing import NewType, NotRequired, TypedDict

StepId = NewType("StepId", int)


class StepRow(TypedDict):
    tour: str
    idx: int
    stars: NotRequired[int]


def label(row: StepRow) -> str:
    return f"{row['tour']}#{row['idx']} ({row.get('stars', 0)} stars)"


row: StepRow = {"tour": "basics", "idx": 3, "stars": 2}
print(label(row))
print(label({"tour": "traits", "idx": 0}))
print(StepId(7) + 1)

How it works

1. TypedDict describes required and optional keys.
2. total=False makes every key optional.
3. NewType is a distinct type at check time, an int at run time.

Keywords and builtins used here

• StepRow
• class
• def
• int
• label
• print
• return
• str

The run, in numbers

Lines

19

Characters to type

395

Tokens

144

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 79 seconds.

Type this snippet

Step 3 of 4 in Typing in depth, step 43 of 53 in Pythonic Python.

← Previous Next →