Fix deprecation warning on Python 3.11

Fixes #192.

Author: adamchainz

Diff for: .github/workflows/ci.yml

@@ -22,7 +22,14 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9]
+        python-version:
+        - '3.5'
+        - '3.6'
+        - '3.7'
+        - '3.8'
+        - '3.9'
+        - '3.10'
+        - '3.11-dev'
 
     steps:
     - uses: actions/checkout@v2
@@ -36,4 +43,4 @@ jobs:
         pip install pytest
     - name: Test with pytest
       run: |
-        pytest
+        python -W error pytest

Diff for: certifi/core.py

@@ -7,11 +7,12 @@
 This module returns the installation location of cacert.pem or its contents.
 """
 import os
-import types
-from typing import Union
+import sys
 
-try:
-    from importlib.resources import path as get_path, read_text
+
+if sys.version_info >= (3, 9):
+
+    from importlib.resources import as_file, files
 
     _CACERT_CTX = None
     _CACERT_PATH = None
@@ -35,36 +36,59 @@ def where() -> str:
             # We also have to hold onto the actual context manager, because
             # it will do the cleanup whenever it gets garbage collected, so
             # we will also store that at the global level as well.
-            _CACERT_CTX = get_path("certifi", "cacert.pem")
+            _CACERT_CTX = as_file(files("certifi").joinpath("cacert.pem"))
             _CACERT_PATH = str(_CACERT_CTX.__enter__())
 
         return _CACERT_PATH
 
+else:
 
-except ImportError:
-    Package = Union[types.ModuleType, str]
-    Resource = Union[str, "os.PathLike"]
-
-    # This fallback will work for Python versions prior to 3.7 that lack the
-    # importlib.resources module but relies on the existing `where` function
-    # so won't address issues with environments like PyOxidizer that don't set
-    # __file__ on modules.
-    def read_text(
-        package: Package,
-        resource: Resource,
-        encoding: str = 'utf-8',
-        errors: str = 'strict'
-    ) -> str:
-        with open(where(), "r", encoding=encoding) as data:
-            return data.read()
-
-    # If we don't have importlib.resources, then we will just do the old logic
-    # of assuming we're on the filesystem and munge the path directly.
-    def where() -> str:
-        f = os.path.dirname(__file__)
+    try:
+        from importlib.resources import path as get_path
+
+        _CACERT_CTX = None
+        _CACERT_PATH = None
+
+        def where() -> str:
+            # This is slightly terrible, but we want to delay extracting the
+            # file in cases where we're inside of a zipimport situation until
+            # someone actually calls where(), but we don't want to re-extract
+            # the file on every call of where(), so we'll do it once then store
+            # it in a global variable.
+            global _CACERT_CTX
+            global _CACERT_PATH
+            if _CACERT_PATH is None:
+                # This is slightly janky, the importlib.resources API wants you
+                # to manage the cleanup of this file, so it doesn't actually
+                # return a path, it returns a context manager that will give
+                # you the path when you enter it and will do any cleanup when
+                # you leave it. In the common case of not needing a temporary
+                # file, it will just return the file system location and the
+                # __exit__() is a no-op.
+                #
+                # We also have to hold onto the actual context manager, because
+                # it will do the cleanup whenever it gets garbage collected, so
+                # we will also store that at the global level as well.
+                _CACERT_CTX = get_path("certifi", "cacert.pem")
+                _CACERT_PATH = str(_CACERT_CTX.__enter__())
+
+            return _CACERT_PATH
+
+    except ImportError:
+        # This fallback will work for Python versions prior to 3.7 that lack
+        # the importlib.resources module but relies on the existing `where`
+        # function so won't address issues with environments like PyOxidizer
+        # that don't set __file__ on modules.
+
+        # If we don't have importlib.resources, then we will just do the old
+        # logic of assuming we're on the filesystem and munge the path
+        # directly.
+        def where() -> str:
+            f = os.path.dirname(__file__)
 
-        return os.path.join(f, "cacert.pem")
+            return os.path.join(f, "cacert.pem")
 
 
 def contents() -> str:
-    return read_text("certifi", "cacert.pem", encoding="ascii")
+    with open(where(), encoding="ascii") as fp:
+        return fp.read()