A real world example of a Python Flask utility class used in the simpledocs.co and chrisandgitte.com projects. The gist shows the progression from a minimum viable product first, to a refactored library class for general use. The unit tests used in the refactor are appended in a final commit for completeness.

RequestParser.py

#
# File lib/requestparser.py
#

class RequestParser:

    def parse(self, flask_request):
        self.request = flask_request
        return self._parse_request()

    def _parse_request(self):
        self.parsed = {}
        self.parsing = self.request.base_url.__str__()
        self._validate_url()
        self._parse_protocol()
        self._parse_domain()
        self._parse_uri_segments()
        self._parse_uri()
        return self.parsed

    def _validate_url(self):
        has_protocol_string = (self.parsing.find('://') != -1)
        if not has_protocol_string:
            raise Exception('Invalid URL')

    def _parse_protocol(self):
        protocol, self.parsing = self.parsing.split('://')
        self.parsed['protocol'] = protocol

    def _parse_domain(self):
        self._parse_into_segments()
        self.parsed['domain'] = self._segments[0]

    def _parse_into_segments(self):
        segments = self.parsing.split('/')
        filtered_segments = [x for x in segments if x]
        self._segments = filtered_segments

    def _parse_uri_segments(self):
        self.parsed['uri_segments'] = self._segments[1:]

    def _parse_uri(self):
        uri_segments = self.parsed.get('uri_segments')
        self.parsed['uri'] = '/' + '/'.join(uri_segments)


#
# File: tests/test-lib/test-requestparser.py
#

# -*- coding: utf8 -*-

# nosetests --with-coverage --cover-package=<package> \
# --nocapture ./tests

import os
from lib.environment import Environment
base_dir = '{0}/../../'.format(__file__)
abs_base_dir = os.path.abspath(base_dir)
Environment().add_virtualenv_site_packages_to_path(abs_base_dir)

from nose.tools import *
from lib.requestparser import RequestParser

class TestRequestParser:

    def setup(self):
        "Set up test fixtures"

    def teardown(self):
        "Tear down test fixtures"

    def test_empty_url_raises_exception(self):
        url = ''

        request = RequestStub().create(url)
        assert_raises(Exception, RequestParser.parse, request)

    def test_invalid_url_raises_exception(self):
        url = 'www.example.com/test/uri.html?one=two'

        request = RequestStub().create(url)
        assert_raises(Exception, RequestParser.parse, request)

    def test_valid_url(self):
        url = 'http://www.example.com/test/uri.html?one=two'
        expected = {
            'protocol': 'http',
            'domain': 'www.example.com',
            'uri': '/test/uri.html',
            'uri_segments': ['test', 'uri.html']
        }

        request = RequestStub().create(url)
        result = RequestParser().parse(request)
        assert_equal(result, expected)

class RequestStub:

    class Object(object):
        " See: http://stackoverflow.com/questions/2827623 "
        pass

    def create(self, url):
        stub = self.Object()
        stub.url = url
        stub.base_url = url.split('?')[0]
        return stub