Adding support for fields that are only included in __init__

Author: jcal-15

argparse_dataclass.py

@@ -238,16 +238,21 @@
     Union,
     Any,
     Generic,
+    ClassVar,
 )
 from dataclasses import (
     Field,
     is_dataclass,
     fields,
     MISSING,
+    InitVar,
     dataclass as real_dataclass,
 )
 from importlib.metadata import version
 
+# This is `typing._GenericAlias` but don't use non-public type names
+_ClassVarType = type(ClassVar[object])
+
 # In Python 3.10, we can use types.NoneType
 NoneType = type(None)
 
@@ -284,14 +289,17 @@ def _add_dataclass_options(
     if not is_dataclass(options_class):
         raise TypeError("cls must be a dataclass")
 
-    for field in fields(options_class):
+    for field in _fields(options_class):
         if not field.init:
             continue  # Ignore fields not in __init__
+        f_type = field.type
+        if _is_initvar(f_type):
+            f_type = f_type.type
 
         args = field.metadata.get("args", [f"--{_get_arg_name(field)}"])
         positional = not args[0].startswith("-")
         kwargs = {
-            "type": field.metadata.get("type", field.type),
+            "type": field.metadata.get("type", f_type),
             "help": field.metadata.get("help", None),
         }
 
@@ -304,7 +312,7 @@ def _add_dataclass_options(
             kwargs["choices"] = field.metadata["choices"]
 
         # Support Literal types as an alternative means of specifying choices.
-        if get_origin(field.type) is Literal:
+        if get_origin(f_type) is Literal:
             # Prohibit a potential collision with the choices field
             if field.metadata.get("choices") is not None:
                 raise ValueError(
@@ -314,7 +322,7 @@ def _add_dataclass_options(
                 )
 
             # Get the types of the arguments of the Literal
-            types = [type(arg) for arg in get_args(field.type)]
+            types = [type(arg) for arg in get_args(f_type)]
 
             # Make sure just a single type has been used
             if len(set(types)) > 1:
@@ -329,7 +337,7 @@ def _add_dataclass_options(
             # Overwrite the type kwarg
             kwargs["type"] = types[0]
             # Use the literal arguments as choices
-            kwargs["choices"] = get_args(field.type)
+            kwargs["choices"] = get_args(f_type)
 
         if field.metadata.get("metavar") is not None:
             kwargs["metavar"] = field.metadata["metavar"]
@@ -343,7 +351,7 @@ def _add_dataclass_options(
                 # did not specify the type of the elements within the list, we
                 # try to infer it:
                 try:
-                    kwargs["type"] = get_args(field.type)[0]  # get_args returns a tuple
+                    kwargs["type"] = get_args(f_type)[0]  # get_args returns a tuple
                 except IndexError:
                     # get_args returned an empty tuple, type cannot be inferred
                     raise ValueError(
@@ -357,12 +365,12 @@ def _add_dataclass_options(
         else:
             kwargs["default"] = MISSING
 
-        if field.type is bool:
+        if f_type is bool:
             _handle_bool_type(field, args, kwargs)
-        elif get_origin(field.type) is Union:
+        elif get_origin(f_type) is Union:
             if field.metadata.get("type") is None:
                 # Optional[X] is equivalent to Union[X, None].
-                f_args = get_args(field.type)
+                f_args = get_args(f_type)
                 if len(f_args) == 2 and NoneType in f_args:
                     arg = next(a for a in f_args if a is not NoneType)
                     kwargs["type"] = arg
@@ -439,6 +447,24 @@ def _get_arg_name(field: Field):
     return field.name.replace("_", "-")
 
 
+def _fields(dataclass) -> Tuple[Field]:
+    # dataclass.fields does not return fields that are of type InitVar
+    dc_fields = getattr(dataclass, "__dataclass_fields__", None)
+    if dc_fields is None:
+        return fields(dataclass)
+    return tuple(f for f in dc_fields.values() if not _is_classvar(f.type))
+
+
+def _is_classvar(a_type):
+    return a_type is ClassVar or (
+        type(a_type) is _ClassVarType and a_type.__origin__ is ClassVar
+    )
+
+
+def _is_initvar(a_type):
+    return a_type is InitVar or type(a_type) is InitVar
+
+
 class ArgumentParser(argparse.ArgumentParser, Generic[OptionsType]):
     """Command line argument parser that derives its options from a dataclass.
 

tests/test_functional.py

@@ -1,7 +1,7 @@
 import sys
 import unittest
 import datetime as dt
-from dataclasses import dataclass, field
+from dataclasses import dataclass, field, InitVar
 
 from typing import Optional, Union
 
@@ -358,6 +358,28 @@ def __post_init__(self):
         self.assertEqual(params.time, "15:35:59")
         self.assertEqual(params.datetime, dt.datetime(1999, 12, 31, 15, 35, 59))
 
+    def test_init_only(self):
+        @dataclass
+        class Options:
+            cls_var: ClassVar[str] = "Hello"
+            date: InitVar[str]
+            time: InitVar[str] = "00:00"
+            datetime: dt.datetime = field(init=False)
+
+            def __post_init__(self, date, time):
+                self.datetime = dt.datetime.fromisoformat(f"{date}T{time}")
+
+        args = ["--date", "1999-12-31"]
+        params = parse_args(Options, args)
+        self.assertFalse(hasattr(params, "date"))
+        # time is always set to the default value. I think this is a bug..
+        # self.assertFalse(hasattr(params, "time"))
+        self.assertEqual(params.datetime, dt.datetime(1999, 12, 31))
+
+        args = ["--date", "1999-12-31", "--time", "15:35:59"]
+        params = parse_args(Options, args)
+        self.assertEqual(params.datetime, dt.datetime(1999, 12, 31, 15, 35, 59))
+
 
 if __name__ == "__main__":
     unittest.main()