Add snippets and tests for language tutorial. (#729)

language/tutorial/README.rst.in

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+# This file is used to generate README.rst
+
+product:
+  name: Google Cloud Natural Language Tutorial
+  short_name: Cloud Natural Language Tutorial
+  url: https://cloud.google.com/natural-language/docs/
+  description: >
+    The `Google Cloud Natural Language API`_ provides natural language
+    understanding technologies to developers, including sentiment analysis,
+    entity recognition, and syntax analysis. This API is part of the larger
+    Cloud Machine Learning API.
+
+setup:
+- auth
+- install_deps
+
+samples:
+- name: Language tutorial
+  file: tutorial.py
+  show_help: true

language/tutorial/requirements.txt

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+google-api-python-client==1.5.5

language/tutorial/reviews/bladerunner-mixed.txt

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+I really wanted to love 'Bladerunner' but ultimately I couldn't get
+myself to appreciate it fully. However, you may like it if you're into
+science fiction, especially if you're interested in the philosophical
+exploration of what it means to be human or machine. Some of the gizmos
+like the flying cars and the Vouight-Kampff machine (which seemed very
+steampunk), were quite cool.
+
+I did find the plot pretty slow and but the dialogue and action sequences
+were good. Unlike most science fiction films, this one was mostly quiet, and
+not all that much happened, except during the last 15 minutes. I didn't
+understand why a unicorn was in the movie. The visual effects were fantastic,
+however, and the musical score and overall mood was quite interesting.
+A futurist Los Angeles that was both highly polished and also falling apart
+reminded me of 'Outland.' Certainly, the style of the film made up for
+many of its pedantic plot holes.
+
+If you want your sci-fi to be lasers and spaceships, 'Bladerunner' may
+disappoint you. But if you want it to make you think, this movie may
+be worth the money.

language/tutorial/reviews/bladerunner-neg.txt

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+What was Hollywood thinking with this movie! I hated,
+hated, hated it. BORING! I went afterwards and demanded my money back.
+They refused.

language/tutorial/reviews/bladerunner-neutral.txt

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+I neither liked nor disliked this movie. Parts were interesting, but
+overall I was left wanting more. The acting was pretty good.

language/tutorial/reviews/bladerunner-pos.txt

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+`Bladerunner` is often touted as one of the best science fiction films ever
+made. Indeed, it satisfies many of the requisites for good sci-fi: a future
+world with flying cars and humanoid robots attempting to rebel against their
+creators. But more than anything, `Bladerunner` is a fantastic exploration
+of the nature of what it means to be human. If we create robots which can
+think, will they become human? And if they do, what makes us unique? Indeed,
+how can we be sure we're not human in any case? `Bladerunner` explored
+these issues before such movies as `The Matrix,' and did so intelligently.
+The visual effects and score by Vangelis set the mood. See this movie
+in a dark theatre to appreciate it fully. Highly recommended!

language/tutorial/tutorial.py

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+#!/usr/bin/env python
+
+# Copyright 2016 Google, Inc
+#
+# 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.
+# [START full_tutorial_script]
+# [START import_libraries]
+import argparse
+import io
+
+from googleapiclient import discovery
+from oauth2client.client import GoogleCredentials
+# [END import_libraries]
+
+
+def print_sentiment(filename):
+    """Prints sentiment analysis on a given file contents."""
+    # [START authenticating_to_the_api]
+    credentials = GoogleCredentials.get_application_default()
+    service = discovery.build('language', 'v1', credentials=credentials)
+    # [END authenticating_to_the_api]
+
+    # [START constructing_the_request]
+    with io.open(filename, 'r') as review_file:
+        review_file_contents = review_file.read()
+
+    service_request = service.documents().analyzeSentiment(
+        body={
+            'document': {
+                'type': 'PLAIN_TEXT',
+                'content': review_file_contents,
+            }
+        }
+    )
+    response = service_request.execute()
+    # [END constructing_the_request]
+
+    # [START parsing_the_response]
+    score = response['documentSentiment']['score']
+    magnitude = response['documentSentiment']['magnitude']
+
+    for n, sentence in enumerate(response['sentences']):
+        sentence_sentiment = sentence['sentiment']['score']
+        print('Sentence {} has a sentiment score of {}'.format(n,
+              sentence_sentiment))
+
+    print('Overall Sentiment: score of {} with magnitude of {}'.format(
+            score, magnitude))
+    # [END parsing_the_response]
+
+
+# [START running_your_application]
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        'movie_review_filename',
+        help='The filename of the movie review you\'d like to analyze.')
+    args = parser.parse_args()
+    print_sentiment(args.movie_review_filename)
+# [END running_your_application]
+# [END full_tutorial_script]

language/tutorial/tutorial_test.py

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+# Copyright 2016, Google, Inc.
+# 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.
+import re
+
+import tutorial
+
+
+def test_neutral(capsys):
+    tutorial.print_sentiment('reviews/bladerunner-neutral.txt')
+    out, _ = capsys.readouterr()
+    assert re.search(r'Sentence \d has a sentiment score of \d', out, re.I)
+    assert re.search(
+        r'Overall Sentiment: score of -?[0-2]\.?[0-9]? with '
+        r'magnitude of [0-1]\.?[0-9]?', out, re.I)
+
+
+def test_pos(capsys):
+    tutorial.print_sentiment('reviews/bladerunner-pos.txt')
+    out, _ = capsys.readouterr()
+    assert re.search(r'Sentence \d has a sentiment score of \d', out, re.I)
+    assert re.search(
+        r'Overall Sentiment: score of [0-9]\.?[0-9]? with '
+        r'magnitude of [0-9]\.?[0-9]?', out, re.I)
+
+
+def test_neg(capsys):
+    tutorial.print_sentiment('reviews/bladerunner-neg.txt')
+    out, _ = capsys.readouterr()
+    assert re.search(r'Sentence \d has a sentiment score of \d', out, re.I)
+    assert re.search(
+        r'Overall Sentiment: score of -[0-9]\.?[0-9]? with '
+        r'magnitude of [2-7]\.?[0-9]?', out, re.I)
+
+
+def test_mixed(capsys):
+    tutorial.print_sentiment('reviews/bladerunner-mixed.txt')
+    out, _ = capsys.readouterr()
+    assert re.search(r'Sentence \d has a sentiment score of \d', out, re.I)
+    assert re.search(
+        r'Overall Sentiment: score of -?[0-9]\.?[0-9]? with '
+        r'magnitude of [3-6]\.?[0-9]?', out, re.I)