Google App Engine dev_appserver.py: watcher_ignore_re flag "is not JSON serializable"

Question

Why I run the dev_appserver.py with the option watcher_ignore_re, I get an error message that the regex is not JSON serializable.

Is this a bug with the development server? Am I using this command improperly? The command and callstack is printed below.

C:\Users\mes65\Documents\MyProject>"C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\bin\dev_appserver.py" ^
    --watcher_ignore_re="(.*\.git|.*\.idea|tmp\.py)" ^
    "C:\Users\mes65\Documents\MyProject"
WARNING  2018-06-06 09:28:59,161 appinfo.py:1622] lxml version "2.3" is deprecated, use one of: "3.7.3"
INFO     2018-06-06 09:28:59,187 devappserver2.py:120] Skipping SDK update check.
Traceback (most recent call last):
  File "C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\dev_appserver.py", line 96, in <module>
    _run_file(__file__, globals())
  File "C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\dev_appserver.py", line 90, in _run_file
    execfile(_PATHS.script_file(script_name), globals_)
  File "C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\tools\devappserver2\devappserver2.py", line 454, in <module>
    main()
  File "C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\tools\devappserver2\devappserver2.py", line 442, in main
    dev_server.start(options)
  File "C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\tools\devappserver2\devappserver2.py", line 163, in start
    bool(ssl_certificate_paths), options)
  File "C:\Program Files (x86)\Google\Cloud SDK\google-cloud-sdk\platform\google_appengine\google\appengine\tools\devappserver2\metrics.py", line 166, in Start
    self._cmd_args = json.dumps(vars(cmd_args)) if cmd_args else None
  File "C:\Python27\lib\json\__init__.py", line 244, in dumps
    return _default_encoder.encode(obj)
  File "C:\Python27\lib\json\encoder.py", line 207, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "C:\Python27\lib\json\encoder.py", line 270, in iterencode
    return _iterencode(o, 0)
  File "C:\Python27\lib\json\encoder.py", line 184, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: <_sre.SRE_Pattern object at 0x00000000063C2188> is not JSON serializable

Answer 1

It looks like it is an issue with the google analytics code built into dev_appserver2 (google-cloud-sdk\platform\google_appengine\google\appengine\tools\devappserver2\devappserver2.py on or around line 316). It wants to send all of your command line options to google analytics. If you remove the analytics client id by adding the command line option --google_analytics_client_id= (note: '=' without any following value) the appserver won't call the google analytics code where it is trying to JSON serialize an SRE object and failing. However, since you are on Windows I find that the --watcher_ignore_re does not work anyway even when you get past this issue.

There is a comment in file_watcher.py

TODO: b/33178251 - Add watcher_ignore_re support for windows.