Variable length tuple field cannot be defined

[bofm]

Bug

For bugs/questions:

• OS: MacOS 10.14.2
• Python version: 3.7.2
• Pydantic version: 0.24

According to Python typing docs

To specify a variable-length tuple of homogeneous type, use literal ellipsis, e.g. Tuple[int, ...]. A plain Tuple is equivalent to Tuple[Any, ...], and in turn to tuple.

Specifying a variable length tuple like this

from typing import Tuple
from pydantic.dataclasses import dataclass

@dataclass(frozen=True)
class User1:
    name: str
    friends: Tuple[str, ...] = tuple()

causes Pydantic to fail:

Traceback (most recent call last):
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/validators.py", line 373, in find_validators
    if issubclass(type_, val_type):
TypeError: issubclass() arg 1 must be a class

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "x.py", line 4, in <module>
    @dataclass(frozen=True)
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/dataclasses.py", line 122, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, config)
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/dataclasses.py", line 85, in _process_class
    cls.__name__, __config__=config, __module__=_cls.__module__, __validators__=validators, **fields
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/main.py", line 574, in create_model
    return type(model_name, (__base__,), namespace)  # type: ignore
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/main.py", line 197, in __new__
    config=config,
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 137, in infer
    schema=schema,
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 106, in __init__
    self.prepare()
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 171, in prepare
    self._populate_sub_fields()
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 202, in _populate_sub_fields
    self._create_sub_type(t, f'{self.name}_{i}') for i, t in enumerate(self.type_.__args__)  # type: ignore
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 202, in <listcomp>
    self._create_sub_type(t, f'{self.name}_{i}') for i, t in enumerate(self.type_.__args__)  # type: ignore
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 232, in _create_sub_type
    model_config=self.model_config,
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 106, in __init__
    self.prepare()
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 172, in prepare
    self._populate_validators()
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/fields.py", line 250, in _populate_validators
    else find_validators(self.type_, self.model_config.arbitrary_types_allowed)
  File "/Users/x/.pyenv/versions/3.7.2/lib/python3.7/site-packages/pydantic/validators.py", line 376, in find_validators
    raise RuntimeError(f'error checking inheritance of {type_!r} (type: {display_as_type(type_)})') from e
RuntimeError: error checking inheritance of Ellipsis (type: ellipsis)

And If we omit the ellipsis Pydantic does not allow us to set the field value to an empty tuple (which is actually correct).

from typing import Tuple
from pydantic.dataclasses import dataclass

@dataclass(frozen=True)
class User2:
    name: str
    friends: Tuple[str] = tuple()

user2 = User2(name='Jimmy', friends=())
print(user2)

pydantic.error_wrappers.ValidationError: 1 validation error
friends
  wrong tuple length 0, expected 1 (type=value_error.tuple.length; actual_length=0; expected_length=1)

[samuelcolvin]

yes, it's not implemented. PR welcome.

[samuelcolvin]

you can use Sequence[str] as a work around.