ARROW-5248: [Python] support zoneinfo / dateutil timezones

cpp/src/arrow/python/datetime.cc

@@ -470,6 +470,32 @@ Result<std::string> TzinfoToString(PyObject* tzinfo) {
     return result;
   }
 
+  // try to look up key attribute
+  // in case of zoneinfo object
+  if (PyObject_HasAttrString(tzinfo, "key")) {
+    OwnedRef key(PyObject_GetAttrString(tzinfo, "key"));
+    RETURN_IF_PYERROR();
+    std::string result;
+    RETURN_NOT_OK(internal::PyUnicode_AsStdString(key.obj(), &result));
+    return result;
+  }
+
+  // try to look up _filename attribute
+  // in case of dateutil.tz object
+  if (PyObject_HasAttrString(tzinfo, "_filename")) {
+    OwnedRef _filename(PyObject_GetAttrString(tzinfo, "_filename"));
+    RETURN_IF_PYERROR();
+    std::string result;
+    RETURN_NOT_OK(internal::PyUnicode_AsStdString(_filename.obj(), &result));
+    // _filename returns a full path in general ('/usr/share/zoneinfo/Europe/Paris')
+    // or POSIX name on Windows ('Europe/Paris') - we need a substring in first case
+    std::size_t pos = result.find("zoneinfo/");
+    if (pos != std::string::npos) {
+      return result.substr(pos + 9);
+    }
+    return result;
+  }
+
   // attempt to call tzinfo.tzname(None)
   OwnedRef tzname_object(PyObject_CallMethod(tzinfo, "tzname", "O", Py_None));
   RETURN_IF_PYERROR();

python/pyarrow/tests/test_types.py

@@ -303,6 +303,25 @@ def test_tzinfo_to_string(tz, expected):
     assert pa.lib.tzinfo_to_string(tz) == expected
 
 
+def test_dateutil_tzinfo_to_string():
+    pytest.importorskip("dateutil")
+    import dateutil.tz
+
+    tz = dateutil.tz.UTC
+    assert pa.lib.tzinfo_to_string(tz) == 'UTC'
+    tz = dateutil.tz.gettz('Europe/Paris')
+    assert pa.lib.tzinfo_to_string(tz) == 'Europe/Paris'
+
+
+def test_zoneinfo_tzinfo_to_string():
+    zoneinfo = pytest.importorskip('zoneinfo')
+
+    tz = zoneinfo.ZoneInfo('UTC')
+    assert pa.lib.tzinfo_to_string(tz) == 'UTC'
+    tz = zoneinfo.ZoneInfo('Europe/Paris')
+    assert pa.lib.tzinfo_to_string(tz) == 'Europe/Paris'
+
+
 def test_tzinfo_to_string_errors():
     msg = "Not an instance of datetime.tzinfo"
     with pytest.raises(TypeError):