Add sigparse.utils.unwrap (#8)

* add the utils function

* add tests

* fix tests

* add tests

* add tests

* support 3.7

* args 3.7

* mypy

sigparse/__init__.py

@@ -27,11 +27,13 @@
 from sigparse._sigparse import sigparse, Parameter
 from sigparse._classparse import classparse, ClassVar
 from sigparse._pep604 import global_PEP604
+from sigparse import utils
 
 __all__: typing.Sequence[str] = (
     "classparse",
     "sigparse",
     "Parameter",
     "ClassVar",
     "global_PEP604",
+    "utils",
 )

sigparse/utils.py

@@ -0,0 +1,54 @@
+import types
+import typing
+
+__all__: typing.Sequence[str] = ("unwrap",)
+
+try:
+    UnionType = types.UnionType  # type: ignore
+except AttributeError:
+    UnionType = ...
+
+NoneType = type(None)
+
+
+def _get_origin(typehint: typing.Any) -> typing.Any:
+    if hasattr(typehint, "__origin__"):
+        return typehint.__origin__
+
+    return None
+
+
+def _get_args(typehint: typing.Any) -> typing.Any:
+    if hasattr(typehint, "__args__"):
+        return typehint.__args__
+
+    return None
+
+
+def unwrap(typehint: typing.Any) -> typing.Any:
+    """
+    Remove the `None` values from a `Union[T, U]` or `Optional[T]`.
+
+    If one of `T` or `U` is `None`, return the non-none value.
+    If `T` and `U` are `None`, return `None`.
+    If neither `T` or `U` are `None`, return `Union[T, U]`.
+    If `typehint` is not a `Union` or `Option` return `typehint`.
+    """
+
+    if typehint is NoneType:
+        return None
+
+    if _get_origin(typehint) not in {typing.Union, UnionType}:
+        return typehint
+
+    args = _get_args(typehint)
+
+    if not args:
+        return None
+
+    hints = list(filter(lambda x: x not in {NoneType, None}, args))
+
+    if len(hints) == 1:
+        return hints[0]
+
+    return typing.Union[hints[0], hints[1]]

tests/test_utils.py

@@ -0,0 +1,13 @@
+import typing
+import sigparse
+
+def test_unwrap():
+    assert sigparse.utils.unwrap(typing.Union[int, None]) == int
+    assert sigparse.utils.unwrap(typing.Union[None, None]) == None
+    assert sigparse.utils.unwrap(typing.Union[int, str]) == typing.Union[int, str]
+
+    assert sigparse.utils.unwrap(typing.Optional[int]) == int
+    assert sigparse.utils.unwrap(typing.Optional[None]) == None
+
+    assert sigparse.utils.unwrap(int) == int
+    assert sigparse.utils.unwrap(None) == None