Pydantic issue for tuple length

Question

I have the following model in pydantic (Version 2.0.3)

from typing import Tuple
from pydantic import BaseModel

class Model(BaseModel):
    test_field: Tuple[int]

But when I enter

model = Model(test_field=(1,2))

I get as error:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "/Users/tobi/Documents/scraiber/z_legacy/fastapi_test_app/venv/lib/python3.10/site-packages/pydantic/main.py", line 150, in __init__
    __pydantic_self__.__pydantic_validator__.validate_python(data, self_instance=__pydantic_self__)
pydantic_core._pydantic_core.ValidationError: 1 validation error for Model
test_field
  Tuple should have at most 1 item after validation, not 2 [type=too_long, input_value=(1, 2), input_type=tuple]
    For further information visit https://errors.pydantic.dev/2.0.3/v/too_long

Do you know how I can fix that?

Answer 1

Following @Tim Robert's Answer, the linked PR suggests using the Ellipsis ... is the syntax you're after!

https://github.com/pydantic/pydantic/pull/512/files

class Model(BaseModel):
    test_field: Tuple[int, ...]

>>> Model(test_field=(1,2))
Model(test_field=(1, 2))

---

I'm don't think it's really advisable, but if you have an exact count of fields, you can generate and expand 'em (also beware, there might be cases where you should use the long form *(int for _ in range(count)) as the inner values will all refer to the same object)

count = 5
class Model_Five(BaseModel):
    test_field: Tuple[*([int]*count)]

>>> Model_Five(test_field=(1,2,3,4,5))
Model_Five(test_field=(1, 2, 3, 4, 5))
>>> Model_Five(test_field=(1,2,3,4))
[..] omitted
test_field.4
  Field required [type=missing, input_value=(1, 2, 3, 4), input_type=tuple]
    For further information visit https://errors.pydantic.dev/2.7/v/missing