1 files changed, 110 insertions, 0 deletions
diff --git a/Lib/zoneinfo/_tzpath.py b/Lib/zoneinfo/_tzpath.py
new file mode 100644
index 0000000..8cff0b1
--- /dev/null
+++ b/Lib/zoneinfo/_tzpath.py
@@ -0,0 +1,110 @@
+import os
+import sys
+import sysconfig
+
+
+def reset_tzpath(to=None):
+    global TZPATH
+
+    tzpaths = to
+    if tzpaths is not None:
+        if isinstance(tzpaths, (str, bytes)):
+            raise TypeError(
+                f"tzpaths must be a list or tuple, "
+                + f"not {type(tzpaths)}: {tzpaths!r}"
+            )
+        elif not all(map(os.path.isabs, tzpaths)):
+            raise ValueError(_get_invalid_paths_message(tzpaths))
+        base_tzpath = tzpaths
+    else:
+        env_var = os.environ.get("PYTHONTZPATH", None)
+        if env_var is not None:
+            base_tzpath = _parse_python_tzpath(env_var)
+        else:
+            base_tzpath = _parse_python_tzpath(
+                sysconfig.get_config_var("TZPATH")
+            )
+
+    TZPATH = tuple(base_tzpath)
+
+
+def _parse_python_tzpath(env_var):
+    if not env_var:
+        return ()
+
+    raw_tzpath = env_var.split(os.pathsep)
+    new_tzpath = tuple(filter(os.path.isabs, raw_tzpath))
+
+    # If anything has been filtered out, we will warn about it
+    if len(new_tzpath) != len(raw_tzpath):
+        import warnings
+
+        msg = _get_invalid_paths_message(raw_tzpath)
+
+        warnings.warn(
+            "Invalid paths specified in PYTHONTZPATH environment variable."
+            + msg,
+            InvalidTZPathWarning,
+        )
+
+    return new_tzpath
+
+
+def _get_invalid_paths_message(tzpaths):
+    invalid_paths = (path for path in tzpaths if not os.path.isabs(path))
+
+    prefix = "\n    "
+    indented_str = prefix + prefix.join(invalid_paths)
+
+    return (
+        "Paths should be absolute but found the following relative paths:"
+        + indented_str
+    )
+
+
+def find_tzfile(key):
+    """Retrieve the path to a TZif file from a key."""
+    _validate_tzfile_path(key)
+    for search_path in TZPATH:
+        filepath = os.path.join(search_path, key)
+        if os.path.isfile(filepath):
+            return filepath
+
+    return None
+
+
+_TEST_PATH = os.path.normpath(os.path.join("_", "_"))[:-1]
+
+
+def _validate_tzfile_path(path, _base=_TEST_PATH):
+    if os.path.isabs(path):
+        raise ValueError(
+            f"ZoneInfo keys may not be absolute paths, got: {path}"
+        )
+
+    # We only care about the kinds of path normalizations that would change the
+    # length of the key - e.g. a/../b -> a/b, or a/b/ -> a/b. On Windows,
+    # normpath will also change from a/b to a\b, but that would still preserve
+    # the length.
+    new_path = os.path.normpath(path)
+    if len(new_path) != len(path):
+        raise ValueError(
+            f"ZoneInfo keys must be normalized relative paths, got: {path}"
+        )
+
+    resolved = os.path.normpath(os.path.join(_base, new_path))
+    if not resolved.startswith(_base):
+        raise ValueError(
+            f"ZoneInfo keys must refer to subdirectories of TZPATH, got: {path}"
+        )
+
+
+del _TEST_PATH
+
+
+class InvalidTZPathWarning(RuntimeWarning):
+    """Warning raised if an invalid path is specified in PYTHONTZPATH."""
+
+
+TZPATH = ()
+reset_tzpath()