Inline distutils.util.strtobool in tests (python-attrs#813)

`distutils` is deprecated in Python 3.10 and slated for removal in
Python 3.12. Fortunately, `attrs` only uses `distutils` once and it's
trivial to remove.

As suggested by @sscherfke, add the `to_bool` converter to
`converters.py`.

Closes python-attrs#813

Co-authored-by: Stefan Scherfke <stefan@sofa-rockers.org>

src/attr/converters.py

@@ -109,3 +109,42 @@ def default_if_none_converter(val):
             return default
 
     return default_if_none_converter
+
+
+def to_bool(val):
+    """
+    Convert "boolean" strings (e.g., from env. vars.) to real booleans.
+
+    Values mapping to :code:`True`:
+
+    - :code:`True`
+    - :code:`"true"` / :code:`"t"`
+    - :code:`"yes"` / :code:`"y"`
+    - :code:`"on"`
+    - :code:`"1"`
+    - :code:`1`
+
+    Values mapping to :code:`False`:
+
+    - :code:`False`
+    - :code:`"false"` / :code:`"f"`
+    - :code:`"no"` / :code:`"n"`
+    - :code:`"off"`
+    - :code:`"0"`
+    - :code:`0`
+
+    Raise :exc:`ValueError` for any other value.
+    """
+    if isinstance(val, str):
+        val = val.lower()
+    truthy = {True, "true", "t", "yes", "y", "on", "1", 1}
+    falsy = {False, "false", "f", "no", "n", "off", "0", 0}
+    try:
+        if val in truthy:
+            return True
+        if val in falsy:
+            return False
+    except TypeError:
+        # Raised when "val" is not hashable (e.g., lists)
+        pass
+    raise ValueError(f"Cannot convert value to bool: {val}")

src/attr/converters.pyi

@@ -10,3 +10,4 @@ def optional(converter: _ConverterType) -> _ConverterType: ...
 def default_if_none(default: _T) -> _ConverterType: ...
 @overload
 def default_if_none(*, factory: Callable[[], _T]) -> _ConverterType: ...
+def to_bool(val: str) -> bool: ...

tests/test_converters.py

@@ -4,14 +4,12 @@
 
 from __future__ import absolute_import
 
-from distutils.util import strtobool
-
 import pytest
 
 import attr
 
 from attr import Factory, attrib
-from attr.converters import default_if_none, optional, pipe
+from attr.converters import default_if_none, optional, pipe, to_bool
 
 
 class TestOptional(object):
@@ -106,15 +104,15 @@ def test_success(self):
         """
         Succeeds if all wrapped converters succeed.
         """
-        c = pipe(str, strtobool, bool)
+        c = pipe(str, to_bool, bool)
 
         assert True is c("True") is c(True)
 
     def test_fail(self):
         """
         Fails if any wrapped converter fails.
         """
-        c = pipe(str, strtobool)
+        c = pipe(str, to_bool)
 
         # First wrapped converter fails:
         with pytest.raises(ValueError):
@@ -131,8 +129,8 @@ def test_sugar(self):
 
         @attr.s
         class C(object):
-            a1 = attrib(default="True", converter=pipe(str, strtobool, bool))
-            a2 = attrib(default=True, converter=[str, strtobool, bool])
+            a1 = attrib(default="True", converter=pipe(str, to_bool, bool))
+            a2 = attrib(default=True, converter=[str, to_bool, bool])
 
         c = C()
         assert True is c.a1 is c.a2