Python type hints: how to do a literal range

Question

I use type hints with pydantic to set return schema for my Python API.

I would like to write a literal type that allows the numbers 0 to 100. This is easy typing it out manually:

from typing import Literal
MyType = Literal[0, 1, 2, ... , 99, 100]

This is not particularly pythonic and I'm looking for a shorthand, essentially:

Literal[range(101)]

Unfortunately the above expects the literal value that is range(101). I have also tried:

Literal[list(range(101))]
Literal[0:101]

However these fail as list and slice are unhashable types.

How do I do this without typing out the numbers 0 through 100?

if I understoof the use case, you can use https://pydantic-docs.helpmanual.io/usage/types/#arguments-to-conint and set min and max values — Artur Shiriev, Mar 26 '21 at 06:15

score 6 · Accepted Answer · answered Dec 06 '21 at 09:03

Try this:

from typing import Literal

A = Literal[1,2]
B = Literal[(1,2)]
print(A == B) # True

C = Literal[tuple(range(100))]
print(C)
# typing.Literal[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 
# 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 
# 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 
# 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 
# 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 
# 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

Unfortunately, this is a pattern to which linters object: 'Type arguments for "Literal" must be None, a literal value (int, bool, str, or bytes), or an enum value' — jmathes, Aug 11 '22 at 21:24

score 3 · Answer 2 · answered Mar 24 '21 at 16:38

3

Literal saves the arguments as Literal.__dict__['__args__'] so you could do something like this

from typing import Literal


mytype = Literal[1]
mytype.__dict__['__args__'] = list(range(1, 101))

answered Mar 24 '21 at 16:38

BeanBagTheCat

435
4
7

score 0 · Answer 3 · answered Mar 26 '21 at 10:33

Specifically for Pydantic, you can use a validator to emulate a Literal range:

from pydantic import BaseModel, validator

class MySchema(BaseModel):
    val: int

    @validator('val')
    def validate_range(cls, v):
        if v < 0 or v > 100:
            raise ValueError('Val must be in the range 0-100')
        return v

Python type hints: how to do a literal range

3 Answers3