Compatibility with Python < 3.10

4 files changed, 54 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index 3da8c99..2dc851e 100755
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
  DNAME := dist/$(shell ./setup.py --name)-$(shell ./setup.py --version).tar.gz
 
 test tests:
-	@pytest -s -q
+	@pytest -s
 
 docs:
 	@./setup.py build_sphinx
diff --git a/setup.cfg b/setup.cfg
index 9df94d5..7b78c03 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -23,8 +23,7 @@ classifiers =
 zip_safe = False
 include_package_data = True
 packages = thcolor, thcolor.builtin
-install_requires =
-  regex
+python_requires = >= 3.6
 
 [options.package_data]
 * = *.txt, *.rst
diff --git a/thcolor/colors.py b/thcolor/colors.py
index afbfd58..d459886 100644
--- a/thcolor/colors.py
+++ b/thcolor/colors.py
@@ -5,11 +5,13 @@
 # *****************************************************************************
 """ Color representations and conversions. """
 
-from collections.abc import Mapping as _Mapping, Sequence as _Sequence
 from math import (
     atan2 as _atan2, ceil as _ceil, cos as _cos, sin as _sin, sqrt as _sqrt,
 )
-from typing import Optional as _Optional, Tuple as _Tuple
+from typing import (
+    Optional as _Optional, Tuple as _Tuple, Mapping as _Mapping,
+    Sequence as _Sequence,
+)
 
 from .angles import (
     Angle as _Angle, DegreesAngle as _DegreesAngle,
diff --git a/thcolor/decoders/base.py b/thcolor/decoders/base.py
index 227b0a6..0f4d7cf 100644
--- a/thcolor/decoders/base.py
+++ b/thcolor/decoders/base.py
@@ -48,6 +48,51 @@ def _factor(x, max_=100):
     return x / max_
 
 
+def _issubclass(cls, types):
+    """ Check if ``cls`` is a subclass of ``types``.
+
+        Until Python 3.10, this function is not aware of the special
+        types available in the standard ``typing`` module; this function
+        aims at fixing this for Python <= 3.9.
+    """
+
+    # Check if is a special case from typing that we know of.
+
+    try:
+        origin = types.__origin__
+    except AttributeError:
+        if types is _Any:
+            return True
+    else:
+        if origin is _Union or origin is _Optional:
+            return any(_issubclass(cls, type_) for type_ in types.__args__)
+
+    # If ``types`` is any iterable type (tuple, list, you name it),
+    # then we check if the class is a subclass of at least one element
+    # in the iterable.
+
+    try:
+        types_iter = iter(types)
+    except TypeError:
+        pass
+    else:
+        return any(_issubclass(cls, type_) for type_ in types)
+
+    # We default on the base ``issubclass`` from here.
+
+    return issubclass(cls, types)
+
+
+def _isinstance(value, types):
+    """ Check if ``cls`` is a subclass of ``types``.
+
+        Until Python 3.10, this function is not aware of the special
+        types available in the standard ``typing`` module; this function
+        aims at fixing this for Python <= 3.9.
+    """
+
+    return _issubclass(type(value), types)
+
 def _get_args(func) -> _Sequence[_Tuple[str, _Any, _Any]]:
     """ Get the arguments from a function in order to
         call it using optional or make an alias.
@@ -861,15 +906,15 @@ class ColorDecoder(_Mapping):
                         func=func_name,
                     )
 
-                if argtype is None or isinstance(arg, argtype):
+                if argtype is None or _isinstance(arg, argtype):
                     pass
                 elif (
-                    issubclass(_Color, argtype) and defaults_to_netscape
+                    _issubclass(_Color, argtype) and defaults_to_netscape
                     and fallback_string is not None
                 ):
                     arg = _SRGBColor.fromnetscapecolorname(fallback_string)
                 elif (
-                    issubclass(_Angle, argtype)
+                    _issubclass(_Angle, argtype)
                     and isinstance(arg, (int, float))
                 ):
                     arg = _DegreesAngle(arg)