Fix where() so that it works with importlib.resources when available (certifi#123)

Author: dstufft

certifi/core.py

@@ -9,7 +9,36 @@
 import os
 
 try:
-    from importlib.resources import read_text
+    from importlib.resources import path as get_path, read_text
+
+    _CACERT_CTX = None
+    _CACERT_PATH = None
+
+    def where():
+        # 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
@@ -19,11 +48,12 @@ def read_text(_module, _path, encoding="ascii"):
         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():
+        f = os.path.dirname(__file__)
 
-def where():
-    f = os.path.dirname(__file__)
-
-    return os.path.join(f, "cacert.pem")
+        return os.path.join(f, "cacert.pem")
 
 
 def contents():