Drop support for PY36

Python dropped support on 2021-12-23. Our policy (#760) is to drop
support on the next point release after Python does.

* Remove py36 tests
* Test multiple recent versions of pypy
* Remove pep562 backport

9 files changed, 14 insertions, 274 deletions

diff --git a/.coveragerc b/.coveragerc
index c28a02a..c785d90 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -3,4 +3,3 @@ omit=
     *site-packages*
     tests/*
     markdown/test_tools.py
-    markdown/pep562.py
diff --git a/.github/workflows/tox.yml b/.github/workflows/tox.yml
index 08cbb49..e2004ad 100644
--- a/.github/workflows/tox.yml
+++ b/.github/workflows/tox.yml
@@ -20,10 +20,8 @@ jobs:
       fail-fast: false
       max-parallel: 4
       matrix:
-        tox-env: [py36, py37, py38, py39, py310, pypy3, pygments]
+        tox-env: [py37, py38, py39, py310, pypy37, pypy38, pypy39, pygments]
         include:
-          - tox-env: py36
-            python-version: '3.6'
           - tox-env: py37
             python-version: '3.7'
           - tox-env: py38
@@ -32,8 +30,12 @@ jobs:
             python-version: '3.9'
           - tox-env: py310
             python-version: '3.10'
-          - tox-env: pypy3
-            python-version: pypy3
+          - tox-env: pypy37
+            python-version: pypy-3.7
+          - tox-env: pypy38
+            python-version: pypy-3.8
+          - tox-env: pypy39
+            python-version: pypy-3.9
           - tox-env: pygments
             python-version: '3.7'
 
@@ -43,7 +45,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Setup Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
diff --git a/docs/change_log/release-3.4.md b/docs/change_log/release-3.4.md
index 7abdf5d..eb36b40 100644
--- a/docs/change_log/release-3.4.md
+++ b/docs/change_log/release-3.4.md
@@ -2,7 +2,7 @@ title: Release Notes for v3.4
 
 # Python-Markdown 3.4 Release Notes
 
-Python-Markdown version 3.4 supports Python versions 3.6, 3.7, 3.8, 3.9, 3.10 and
+Python-Markdown version 3.4 supports Python versions 3.7, 3.8, 3.9, 3.10 and
 PyPy3.
 
 ## Backwards-incompatible changes
diff --git a/markdown/__init__.py b/markdown/__init__.py
index e05af10..7760a0c 100644
--- a/markdown/__init__.py
+++ b/markdown/__init__.py
@@ -27,8 +27,6 @@ if sys.version_info[0] < 3:  # pragma: no cover
     raise ImportError('A recent version of Python 3 is required.')
 
 from .core import Markdown, markdown, markdownFromFile  # noqa: E402
-from .util import PY37                                  # noqa: E402
-from .pep562 import Pep562                              # noqa: E402
 from .__meta__ import __version__, __version_info__     # noqa: E402
 import warnings                                         # noqa: E402
 
@@ -51,11 +49,7 @@ def __getattr__(name):
         warnings.warn(
             "'{}' is deprecated. Use '{}' instead.".format(name, deprecated[0]),
             category=DeprecationWarning,
-            stacklevel=(3 if PY37 else 4)
+            stacklevel=(3 if (3, 7) <= sys.version_info else 4)
         )
         return deprecated[1]
     raise AttributeError("module '{}' has no attribute '{}'".format(__name__, name))
-
-
-if not PY37:
-    Pep562(__name__)
diff --git a/markdown/__meta__.py b/markdown/__meta__.py
index 84884b6..92dd5cf 100644
--- a/markdown/__meta__.py
+++ b/markdown/__meta__.py
@@ -26,7 +26,7 @@ License: BSD (see LICENSE.md for details).
 # (1, 2, 0, 'beta', 2) => "1.2b2"
 # (1, 2, 0, 'rc', 4) => "1.2rc4"
 # (1, 2, 0, 'final', 0) => "1.2"
-__version_info__ = (3, 3, 7, 'final', 0)
+__version_info__ = (3, 4, 0, 'dev', 0)
 
 
 def _get_version(version_info):
diff --git a/markdown/pep562.py b/markdown/pep562.py
deleted file mode 100644
index b130d3b..0000000
--- a/markdown/pep562.py
+++ /dev/null
@@ -1,245 +0,0 @@
-"""
-Backport of PEP 562.
-
-https://pypi.org/search/?q=pep562
-
-Licensed under MIT
-Copyright (c) 2018 Isaac Muse <isaacmuse@gmail.com>
-
-Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
-documentation files (the "Software"), to deal in the Software without restriction, including without limitation
-the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
-and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all copies or substantial portions
-of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
-TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
-THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
-CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
-IN THE SOFTWARE.
-"""
-import sys
-from collections import namedtuple
-import re
-
-__all__ = ('Pep562',)
-
-RE_VER = re.compile(
-    r'''(?x)
-    (?P<major>\d+)(?:\.(?P<minor>\d+))?(?:\.(?P<micro>\d+))?
-    (?:(?P<type>a|b|rc)(?P<pre>\d+))?
-    (?:\.post(?P<post>\d+))?
-    (?:\.dev(?P<dev>\d+))?
-    '''
-)
-
-REL_MAP = {
-    ".dev": "",
-    ".dev-alpha": "a",
-    ".dev-beta": "b",
-    ".dev-candidate": "rc",
-    "alpha": "a",
-    "beta": "b",
-    "candidate": "rc",
-    "final": ""
-}
-
-DEV_STATUS = {
-    ".dev": "2 - Pre-Alpha",
-    ".dev-alpha": "2 - Pre-Alpha",
-    ".dev-beta": "2 - Pre-Alpha",
-    ".dev-candidate": "2 - Pre-Alpha",
-    "alpha": "3 - Alpha",
-    "beta": "4 - Beta",
-    "candidate": "4 - Beta",
-    "final": "5 - Production/Stable"
-}
-
-PRE_REL_MAP = {"a": 'alpha', "b": 'beta', "rc": 'candidate'}
-
-
-class Version(namedtuple("Version", ["major", "minor", "micro", "release", "pre", "post", "dev"])):
-    """
-    Get the version (PEP 440).
-
-    A biased approach to the PEP 440 semantic version.
-
-    Provides a tuple structure which is sorted for comparisons `v1 > v2` etc.
-      (major, minor, micro, release type, pre-release build, post-release build, development release build)
-    Release types are named in is such a way they are comparable with ease.
-    Accessors to check if a development, pre-release, or post-release build. Also provides accessor to get
-    development status for setup files.
-
-    How it works (currently):
-
-    - You must specify a release type as either `final`, `alpha`, `beta`, or `candidate`.
-    - To define a development release, you can use either `.dev`, `.dev-alpha`, `.dev-beta`, or `.dev-candidate`.
-      The dot is used to ensure all development specifiers are sorted before `alpha`.
-      You can specify a `dev` number for development builds, but do not have to as implicit development releases
-      are allowed.
-    - You must specify a `pre` value greater than zero if using a prerelease as this project (not PEP 440) does not
-      allow implicit prereleases.
-    - You can optionally set `post` to a value greater than zero to make the build a post release. While post releases
-      are technically allowed in prereleases, it is strongly discouraged, so we are rejecting them. It should be
-      noted that we do not allow `post0` even though PEP 440 does not restrict this. This project specifically
-      does not allow implicit post releases.
-    - It should be noted that we do not support epochs `1!` or local versions `+some-custom.version-1`.
-
-    Acceptable version releases:
-
-    ```
-    Version(1, 0, 0, "final")                    1.0
-    Version(1, 2, 0, "final")                    1.2
-    Version(1, 2, 3, "final")                    1.2.3
-    Version(1, 2, 0, ".dev-alpha", pre=4)        1.2a4
-    Version(1, 2, 0, ".dev-beta", pre=4)         1.2b4
-    Version(1, 2, 0, ".dev-candidate", pre=4)    1.2rc4
-    Version(1, 2, 0, "final", post=1)            1.2.post1
-    Version(1, 2, 3, ".dev")                     1.2.3.dev0
-    Version(1, 2, 3, ".dev", dev=1)              1.2.3.dev1
-    ```
-
-    """
-
-    def __new__(cls, major, minor, micro, release="final", pre=0, post=0, dev=0):
-        """Validate version info."""
-
-        # Ensure all parts are positive integers.
-        for value in (major, minor, micro, pre, post):
-            if not (isinstance(value, int) and value >= 0):
-                raise ValueError("All version parts except 'release' should be integers.")
-
-        if release not in REL_MAP:
-            raise ValueError("'{}' is not a valid release type.".format(release))
-
-        # Ensure valid pre-release (we do not allow implicit pre-releases).
-        if ".dev-candidate" < release < "final":
-            if pre == 0:
-                raise ValueError("Implicit pre-releases not allowed.")
-            elif dev:
-                raise ValueError("Version is not a development release.")
-            elif post:
-                raise ValueError("Post-releases are not allowed with pre-releases.")
-
-        # Ensure valid development or development/pre release
-        elif release < "alpha":
-            if release > ".dev" and pre == 0:
-                raise ValueError("Implicit pre-release not allowed.")
-            elif post:
-                raise ValueError("Post-releases are not allowed with pre-releases.")
-
-        # Ensure a valid normal release
-        else:
-            if pre:
-                raise ValueError("Version is not a pre-release.")
-            elif dev:
-                raise ValueError("Version is not a development release.")
-
-        return super().__new__(cls, major, minor, micro, release, pre, post, dev)
-
-    def _is_pre(self):
-        """Is prerelease."""
-
-        return self.pre > 0
-
-    def _is_dev(self):
-        """Is development."""
-
-        return bool(self.release < "alpha")
-
-    def _is_post(self):
-        """Is post."""
-
-        return self.post > 0
-
-    def _get_dev_status(self):  # pragma: no cover
-        """Get development status string."""
-
-        return DEV_STATUS[self.release]
-
-    def _get_canonical(self):
-        """Get the canonical output string."""
-
-        # Assemble major, minor, micro version and append `pre`, `post`, or `dev` if needed..
-        if self.micro == 0:
-            ver = "{}.{}".format(self.major, self.minor)
-        else:
-            ver = "{}.{}.{}".format(self.major, self.minor, self.micro)
-        if self._is_pre():
-            ver += '{}{}'.format(REL_MAP[self.release], self.pre)
-        if self._is_post():
-            ver += ".post{}".format(self.post)
-        if self._is_dev():
-            ver += ".dev{}".format(self.dev)
-
-        return ver
-
-
-def parse_version(ver, pre=False):
-    """Parse version into a comparable Version tuple."""
-
-    m = RE_VER.match(ver)
-
-    # Handle major, minor, micro
-    major = int(m.group('major'))
-    minor = int(m.group('minor')) if m.group('minor') else 0
-    micro = int(m.group('micro')) if m.group('micro') else 0
-
-    # Handle pre releases
-    if m.group('type'):
-        release = PRE_REL_MAP[m.group('type')]
-        pre = int(m.group('pre'))
-    else:
-        release = "final"
-        pre = 0
-
-    # Handle development releases
-    dev = m.group('dev') if m.group('dev') else 0
-    if m.group('dev'):
-        dev = int(m.group('dev'))
-        release = '.dev-' + release if pre else '.dev'
-    else:
-        dev = 0
-
-    # Handle post
-    post = int(m.group('post')) if m.group('post') else 0
-
-    return Version(major, minor, micro, release, pre, post, dev)
-
-
-class Pep562:
-    """
-    Backport of PEP 562 <https://pypi.org/search/?q=pep562>.
-
-    Wraps the module in a class that exposes the mechanics to override `__dir__` and `__getattr__`.
-    The given module will be searched for overrides of `__dir__` and `__getattr__` and use them when needed.
-    """
-
-    def __init__(self, name):
-        """Acquire `__getattr__` and `__dir__`, but only replace module for versions less than Python 3.7."""
-
-        self._module = sys.modules[name]
-        self._get_attr = getattr(self._module, '__getattr__', None)
-        self._get_dir = getattr(self._module, '__dir__', None)
-        sys.modules[name] = self
-
-    def __dir__(self):
-        """Return the overridden `dir` if one was provided, else apply `dir` to the module."""
-
-        return self._get_dir() if self._get_dir else dir(self._module)
-
-    def __getattr__(self, name):
-        """Attempt to retrieve the attribute from the module, and if missing, use the overridden function if present."""
-
-        try:
-            return getattr(self._module, name)
-        except AttributeError:
-            if self._get_attr:
-                return self._get_attr(name)
-            raise
-
-
-__version_info__ = Version(1, 0, 0, "final")
-__version__ = __version_info__._get_canonical()
diff --git a/markdown/util.py b/markdown/util.py
index a6a32bf..6d3a195 100644
--- a/markdown/util.py
+++ b/markdown/util.py
@@ -27,10 +27,6 @@ from collections import namedtuple
 from functools import wraps, lru_cache
 from itertools import count
 
-from .pep562 import Pep562
-
-PY37 = (3, 7) <= sys.version_info
-
 
 # TODO: Remove deprecated variables in a future release.
 __deprecated__ = {
@@ -462,11 +458,7 @@ def __getattr__(name):
         warnings.warn(
             "'{}' is deprecated. Use '{}' instead.".format(name, deprecated[0]),
             category=DeprecationWarning,
-            stacklevel=(3 if PY37 else 4)
+            stacklevel=(3 if (3, 7) <= sys.version_info else 4)
         )
         return deprecated[1]
     raise AttributeError("module '{}' has no attribute '{}'".format(__name__, name))
-
-
-if not PY37:
-    Pep562(__name__)
diff --git a/setup.py b/setup.py
index 24b01f6..c6eb6af 100755
--- a/setup.py
+++ b/setup.py
@@ -73,7 +73,7 @@ setup(
     maintainer_email='python.markdown@gmail.com',
     license='BSD License',
     packages=['markdown', 'markdown.extensions'],
-    python_requires='>=3.6',
+    python_requires='>=3.7',
     install_requires=["importlib-metadata>=4.4;python_version<'3.10'"],
     extras_require={
         'testing': [
@@ -113,7 +113,6 @@ setup(
         'Operating System :: OS Independent',
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
diff --git a/tox.ini b/tox.ini
index 62523f9..0c76754 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py36, py37, py38, py39, py310, pypy3, pygments, flake8, checkspelling, pep517check, checklinks
+envlist = py{37, 38, 39, 310}, pypy{37, 38, 39}, pygments, flake8, checkspelling, pep517check, checklinks
 isolated_build = True
 
 [testenv]
@@ -41,4 +41,3 @@ skip_install = true
 
 [flake8]
 max-line-length = 119
-exclude=markdown/pep562.py