Fix add_argparse_args raising TypeError with Python 3.6

CHANGELOG.md

@@ -339,6 +339,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `BasePredictionWriter` not returning the batch_indices in a non-distributed setting ([#9432](https://github.com/PyTorchLightning/pytorch-lightning/pull/9432))
 
 
+- Fixed `add_argparse_args` raising `TypeError` when args are typed as `typing.Generic` in Python 3.6 ([#9554](https://github.com/PyTorchLightning/pytorch-lightning/pull/9554))
+
+
 ## [1.4.7] - 2021-09-14
 
 - Fixed logging of nan parameters ([#9364](https://github.com/PyTorchLightning/pytorch-lightning/pull/9364))

pytorch_lightning/utilities/argparse.py

@@ -139,7 +139,7 @@ def get_init_arguments_and_types(cls: Any) -> List[Tuple[str, Tuple, Any]]:
         arg_default = cls_default_params[arg].default
         try:
             arg_types = tuple(arg_type.__args__)
-        except AttributeError:
+        except (AttributeError, TypeError):
             arg_types = (arg_type,)
 
         name_type_default.append((arg, arg_types, arg_default))

tests/utilities/test_argparse.py

@@ -1,6 +1,6 @@
 import io
 from argparse import ArgumentParser, Namespace
-from typing import List
+from typing import Generic, List, TypeVar
 from unittest.mock import MagicMock
 
 import pytest
@@ -137,6 +137,16 @@ def __init__(self, my_parameter: int = 0):
         pass
 
 
+class AddArgparseArgsExampleClassGeneric:
+    T = TypeVar("T")
+
+    class SomeClass(Generic[T]):
+        pass
+
+    def __init__(self, invalid_class: SomeClass):
+        pass
+
+
 def extract_help_text(parser):
     help_str_buffer = io.StringIO()
     parser.print_help(file=help_str_buffer)
@@ -203,6 +213,12 @@ def test_add_argparse_args_no_argument_group():
     assert args.my_parameter == 2
 
 
+def test_add_argparse_args_invalid():
+    """Test that `add_argparse_args` doesn't raise `TypeError` when a class has args typed as `typing.Generic` in
+    Python 3.6."""
+    add_argparse_args(AddArgparseArgsExampleClassGeneric, ArgumentParser())
+
+
 def test_gpus_allowed_type():
     assert _gpus_allowed_type("1,2") == "1,2"
     assert _gpus_allowed_type("1") == 1