I had a little fight with Marshmallow and the ordered=True in class Meta. When ordered=True is set the fields should be outputed in the order specified in the property fields of the class Meta.

Example:

class AuthorSchema(ma.Schema):
    id = base_fields.Int(dump_only=True)

    absolute_url = ma.AbsoluteURLFor('api.author', id='<id>')

    links = ma.Hyperlinks({
        'self': ma.URLFor('api.author', id='<id>'),
        'collection': ma.URLFor('api.authors')
    })

    @post_dump(pass_many=True)
    def wrap(self, data, many):
        key = 'authors' if many else 'author'
        return {
            key: data
        }

    class Meta:
        fields = (
            'id',
            'name',
            'links',
            'absolute_url',
        )
        ordered = True

This was the output.

{
  "author": {
    "absolute_url": "http://localhost:8080/api/v4/authors/123",
    "id": 123,
    "links": {
      "collection": "/api/v4/authors/",
      "self": "/api/v4/authors/123"
    },
    "name": "Fred Douglass"
  }
}

After some Googeling I found out that the culprit was Flask.jsonify. It orders output alphabetically by default. The following setting switches this off.

app.config['JSON_SORT_KEYS'] = False

After this the output was in the specified order.

{
  "author": {
    "id": 123,
    "name": "Fred Douglass",
    "links": {
      "self": "/api/v4/authors/123",
      "collection": "/api/v4/authors/"
    },
    "absolute_url": "http://localhost:8080/api/v4/authors/123"
  }
}

Hope this saves someone else time.

If you need to know which Flask routes are configured you can execute the following command.

print flask_app.url_map

I was busy debugging a rest services I’m building in Flask and Flask-Restplus. I needed a way to log the request and response. I found some code that can be used as a wrapper of the WSGI application that does just this.

Create a file called dubug.py that contains the following code.

import pprint

class RequestLoggingWrapper(object):
    def __init__(self, app):
        self._app = app

    def __call__(self, environ, resp):
        errorlog = environ['wsgi.errors']
        pprint.pprint(('REQUEST', environ), stream=errorlog)

        def log_response(status, headers, *args):
            pprint.pprint(('RESPONSE', status, headers), stream=errorlog)
            return resp(status, headers, *args)

        return self._app(environ, log_response)

This wrapper works independently from Flask and wraps the WSGI application. It shows exactly what request is going in and what response is going out.

When running Flask with the built-in server you can use it as follows.

from debug import RequestLoggingWrapper

if __name__ == '__main__':
    app.wsgi_app = RequestLoggingWrapper(app.wsgi_app)
    app.run()

The output goes to the wgi.error stream. For the built Flask server it is printed to stderr.

I needed to debug the Flask request. After googeling around for a while I ran into a cool trick on Stack Overflow using the pprint module. The pprint module provides a capability to “pretty-print” arbitrary Python data structures in a form which can be used as input to the interpreter.

import pprint
str = pprint.pformat(request.environ, depth=5)

This same trick can be used with all the Flask variables.

• request.args: the key/value pairs in the URL query string
• request.form: the key/value pairs in the body, as sent by a HTML POST form
• request.files: the files in the body, which Flask keeps separate from form
• request.values: combined args and form, preferring args if keys overlap