Fix error message for gettz when passed bytes

AUTHORS.md

@@ -115,7 +115,7 @@ switch, and thus all their contributions are dual-licensed.
 - bjv <brandon.vanvaerenbergh@MASKED> (@bjamesvERT)
 - gl <gl@MASKED>
 - gfyoung <gfyoung17@gmail.com> **D**
-- labrys <labrys@MASKED> (gh: @labrys) **R**
+- Labrys <labrys.git@gmail.com> (gh: @labrys) **R**
 - ms-boom <ms-boom@MASKED>
 - ryanss <ryanssdev@MASKED> (gh: @ryanss) **R**
 

changelog.d/935.misc.rst

@@ -0,0 +1 @@
+Raise a more helpful TypeError message when passing a bytes zonename to gettz in Python 3.  Reported by @labrys (gh issue #927). Fixed by @labrys (gh pr #935)

dateutil/test/test_tz.py

@@ -1102,6 +1102,36 @@ def test_gettz_badzone_unicode():
     assert tzi is None
 
 
+@pytest.mark.gettz
+@pytest.mark.parametrize(
+    "badzone,exc_reason",
+    [
+        pytest.param(
+            b"America/New_York",
+            ".*should be str, not bytes.*",
+            id="bytes on Python 3",
+            marks=[
+                pytest.mark.skipif(
+                    PY2, reason="bytes arguments accepted in Python 2"
+                )
+            ],
+        ),
+        pytest.param(
+            object(),
+            None,
+            id="no startswith()",
+            marks=[
+                pytest.mark.xfail(reason="AttributeError instead of TypeError",
+                                  raises=AttributeError),
+            ],
+        ),
+    ],
+)
+def test_gettz_zone_wrong_type(badzone, exc_reason):
+    with pytest.raises(TypeError, match=exc_reason):
+        tz.gettz(badzone)
+
+
 @pytest.mark.gettz
 @pytest.mark.xfail(IS_WIN, reason='zoneinfo separately cached')
 def test_gettz_cache_clear():

dateutil/tz/tz.py

@@ -1615,8 +1615,15 @@ def nocache(name=None):
                 else:
                     tz = tzlocal()
             else:
-                if name.startswith(":"):
-                    name = name[1:]
+                try:
+                    if name.startswith(":"):
+                        name = name[1:]
+                except TypeError as e:
+                    if isinstance(name, bytes):
+                        new_msg = "gettz argument should be str, not bytes"
+                        six.raise_from(TypeError(new_msg), e)
+                    else:
+                        raise
                 if os.path.isabs(name):
                     if os.path.isfile(name):
                         tz = tzfile(name)