# Copyright 2018 Google LLC

#

# 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 gmail_quickstart]

from __future__ import print_function

import os.path

from googleapiclient.discovery import build

from google_auth_oauthlib.flow import InstalledAppFlow

from google.auth.transport.requests import Request

from google.oauth2.credentials import Credentials

# If modifying these scopes, delete the file token.json.

SCOPES = ['https://www.googleapis.com/auth/gmail.readonly']

def main():

"""Shows basic usage of the Gmail API.

Lists the user's Gmail labels.

"""

creds = None

# The file token.json stores the user's access and refresh tokens, and is

# created automatically when the authorization flow completes for the first

# time.

if os.path.exists('token.json'):

creds = Credentials.from_authorized_user_file('token.json', SCOPES)

# If there are no (valid) credentials available, let the user log in.

if not creds or not creds.valid:

if creds and creds.expired and creds.refresh_token:

creds.refresh(Request())

else:

flow = InstalledAppFlow.from_client_secrets_file(

'credentials.json', SCOPES)

creds = flow.run_local_server(port=0)

# Save the credentials for the next run

with open('token.json', 'w') as token:

token.write(creds.to_json())

service = build('gmail', 'v1', credentials=creds)

# Call the Gmail API

results = service.users().labels().list(userId='me').execute()

labels = results.get('labels', [])

if not labels:

print('No labels found.')

else:

print('Labels:')

for label in labels:

print(label['name'])

if __name__ == '__main__':

main()

# [END gmail_quickstart]