adding clarifying comments

.travis.yml

@@ -42,7 +42,8 @@ matrix:
     #   env: MODE=debops_common VER=2.10.0
 
     # Sanity check against vanilla Ansible. One job suffices.
-    # https://github.com/dw/mitogen/pull/715#issuecomment-719266420 migrating to Azure for now
+    # https://github.com/dw/mitogen/pull/715#issuecomment-719266420 migrating to Azure for now due to Travis 50 min time limit cap
+    # azure lets us adjust the cap, and the current STRATEGY=linear tests take up to 1.5 hours to finish
     # - python: "2.7"
     #   env: MODE=ansible VER=2.10.0 DISTROS=debian STRATEGY=linear
 

mitogen/master.py

@@ -212,6 +212,10 @@ def _py_filename(path):
     if basepath in SPECIAL_FILE_PATHS:
         return path, True
 
+    # return None, False means that the filename passed to _py_filename does not appear
+    # to be python, and code later will handle when this function returns None
+    # see https://github.com/dw/mitogen/pull/715#discussion_r532380528 for how this
+    # decision was made to handle non-python files in this manner
     return None, False