New Maps-Engine sample.

Reviewed in https://codereview.appspot.com/36120043/.

Index: samples/maps_engine/README
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samples/maps_engine/README

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+This sample code demonstrates use of Google Maps Engine. These samples do not
+make use of the Discovery Service, but do use the the httplib2 library to make
+authenticated requests.  For more information on Google Maps Engine, see
+developers.google.com/maps-engine/documentation/
+
+api: mapsengine
+keywords: maps engine mapsengine
+author: Josh Livni

samples/maps_engine/sample_tools.py

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+#  Copyright 2013 Google Inc. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Utilities for making samples.
+
+Consolidates a lot of code commonly repeated in sample applications.
+
+This modified version returns http instead of a built service.  Originally
+https://google-api-python-client.googlecode.com/hg/apiclient/sample_tools.py
+"""
+
+__author__ = 'jcgregorio@google.com (Joe Gregorio)'
+__all__ = ['init']
+
+
+import argparse
+import os
+
+import httplib2
+from oauth2client import client
+from oauth2client import file as oauth2client_file
+from oauth2client import tools
+
+
+def init(argv, name, version, doc, filename, scope=None, parents=[]):
+  """A common initialization routine for samples.
+
+  Many of the sample applications do the same initialization, which has now
+  been consolidated into this function. This function uses common idioms found
+  in almost all the samples, i.e. for an API with name 'apiname', the
+  credentials are stored in a file named apiname.dat, and the
+  client_secrets.json file is stored in the same directory as the application
+  main file.
+
+  Args:
+    argv: list of string, the command-line parameters of the application.
+    name: string, name of the API.
+    version: string, version of the API.
+    doc: string, description of the application. Usually set to __doc__.
+    filename: string, filename of the application. Usually set to __file__.
+    scope: string, The OAuth scope used.
+    parents: list of argparse.ArgumentParser, additional command-line flags.
+
+  Returns:
+    A tuple of (http, flags), where http is the authenticated http object and
+    flags is the parsed command-line flags.
+  """
+  if scope is None:
+    scope = 'https://www.googleapis.com/auth/' + name
+
+  # Parser command-line arguments.
+  parent_parsers = [tools.argparser]
+  parent_parsers.extend(parents)
+  parser = argparse.ArgumentParser(
+      description=doc,
+      formatter_class=argparse.RawDescriptionHelpFormatter,
+      parents=parent_parsers)
+  flags = parser.parse_args(argv[1:])
+
+  # Name of a file containing the OAuth 2.0 information for this
+  # application, including client_id and client_secret, which are found
+  # on the API Access tab on the Google APIs
+  # Console <http://code.google.com/apis/console>.
+  client_secrets = os.path.join(os.path.dirname(filename),
+                                'client_secrets.json')
+
+  # Set up a Flow object to be used if we need to authenticate.
+  flow = client.flow_from_clientsecrets(
+      client_secrets,
+      scope=scope,
+      message=tools.message_if_missing(client_secrets))
+
+  # Prepare credentials, and authorize HTTP object with them.
+  # If the credentials don't exist or are invalid run through the native client
+  # flow. The Storage object will ensure that if successful the good
+  # credentials will get written back to a file.
+  storage = oauth2client_file.Storage(name + '.dat')
+  credentials = storage.get()
+  if credentials is None or credentials.invalid:
+    credentials = tools.run_flow(flow, storage, flags)
+  http = credentials.authorize(http=httplib2.Http())
+
+  # GME does not publish a discovery document, so we return the auth'd http
+  # instead of building a service using the discovery module.
+  return (http, flags)