First of all, thanks for developing pytkdocs!

I do not use pytkdocs directly, but rather mkdocs and mkdocstrings which call pytkdocs.
Here is an example for reproduction.

import pandera as pa
from pandera.typing import DataFrame
from pandera.typing import Series

class Foo(pa.DataFrameModel):
    """
    Some description
    """
    bar: Series[int]

cause_error = DataFrame[Foo]({"bar": [1,2,3]})

Without any instantiated code (that actually uses the panderas models) it runs just fine. But, as soon as I USE the models somewhere in some precomputed objects pytkdocs runs into the following errors:

ERROR    -  mkdocstrings: 'tuple' object has no attribute 'required'
            Traceback (most recent call last):
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/cli.py", line 205, in main
                output = json.dumps(process_json(line))
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/cli.py", line 114, in process_json
                return process_config(json.loads(json_input))
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/cli.py", line 91, in process_config
                obj = loader.get_object_documentation(path, members)
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/loader.py", line 358, in get_object_documentation
                root_object = self.get_module_documentation(leaf, members)
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/loader.py", line 426, in get_module_documentation
                root_object.add_child(self.get_class_documentation(child_node))
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/loader.py", line 544, in get_class_documentation
                self.add_fields(
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/loader.py", line 612, in add_fields
                root_object.add_child(add_method(child_node))
              File "/usr/local/lib/python3.10/dist-packages/pytkdocs/loader.py", line 712, in get_pydantic_field_documentation
                if prop.required:
            AttributeError: 'tuple' object has no attribute 'required'

It seems these pandera models are detected as pydantic, but they do not have the same attributes.
For proper pydantic classes we have this:

from pydantic import BaseModel
class Test(BaseModel):
    i: int
Test.__fields__["i"]
# yields True

For pandera models we seem to have this

import pandera as pa
from pandera.typing import Series
from pandera.typing import DataFrame

class Foo(pa.DataFrameModel):
    bar: Series[int]

Foo.__fields__
# is {}
foo = DataFrame[Foo]({"bar": [1,2,3]})
# after instantiating things exist and probably that's why it causes errors in pytkdocs
Foo.__fields__["bar"]
# <pandera.typing.common.AnnotationInfo at 0x7f...>, <pandera.api.pandas.model_components.FieldInfo("bar") object at 0x7f1...>)

pytkdocs 0.16.1, python 3.10.7, Linux
pydantic 1.10.11 with pydantic_core 2.1.2 (pandera imposes a restriction of pydantic <2)
pandera 0.15.2