Add types to compat module (#6029)

* Add types to compat module

* Refine types

snmp/datadog_checks/snmp/compat.py

@@ -1,21 +1,29 @@
+# (C) Datadog, Inc. 2020-present
+# All rights reserved
+# Licensed under Simplified BSD License (see LICENSE)
+from typing import Any, Optional
+
 try:
     from datadog_checks.base.utils.common import total_time_to_temporal_percent
 except ImportError:
 
     # Provide fallback for agent < 6.16
-    def total_time_to_temporal_percent(total_time, scale=1000):
+    def total_time_to_temporal_percent(total_time, scale=1000):  # type: ignore
         return total_time / scale * 100
 
 
 try:
     from datadog_agent import get_config, read_persistent_cache, write_persistent_cache
 except ImportError:
 
-    def get_config(value):
+    def get_config(key):
+        # type: (str) -> Optional[str]
         return ''
 
-    def write_persistent_cache(value, key):
+    def write_persistent_cache(key, value):
+        # type: (str, str) -> None
         pass
 
-    def read_persistent_cache(value):
+    def read_persistent_cache(key):
+        # type: (str) -> Optional[str]
         return ''

snmp/tox.ini

@@ -9,6 +9,12 @@ envlist =
 description =
     py{27,38}: e2e ready
 dd_check_style = true
+dd_check_types = true
+dd_mypy_args =
+    --py2
+    --disallow-untyped-defs
+    --follow-imports silent
+    datadog_checks/snmp/compat.py
 usedevelop = true
 platform = linux|darwin|win32
 deps =