Gmail API: How can I get the message body?

According to the documentation referenced below a Message should contain a MessagePart which in turn should contain a MessagePartBody.

https://developers.google.com/gmail/api/reference/rest/v1/users.messages#Message

When I run the code below (it's just a modified version of the sample script found here with messages substituted for labels)

from __future__ import print_function
import pickle
import os.path
import openpyxl
from googleapiclient.discovery import build
from google_auth_oauthlib.flow import InstalledAppFlow
from google.auth.transport.requests import Request

# If modifying these scopes, delete the file token.pickle.
SCOPES = ['https://mail.google.com/']

def main():
    """Shows basic usage of the Gmail API.
    Lists the user's Gmail labels.
    """
    creds = None
    # The file token.pickle 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.pickle'):
        with open('token.pickle', 'rb') as token:
            creds = pickle.load(token)
    # 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.pickle', 'wb') as token:
            pickle.dump(creds, token)

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

    # Call the Gmail API
    results = service.users().messages().list(userId='me').execute()
    messages = results.get('messages', [])

    if not messages:
        print('No messages found.')
    else:
        print('Messages:')
        for message in messages:
            print(message)

if __name__ == '__main__':
    main()

I get only Messageids and Threadsids eg:

Messages:
{'id': '177045ba844e1991', 'threadId': '177045ba844e1991'}
{'id': '1770415ccdd222d7', 'threadId': '1770415ccdd222d7'}
{'id': '17703970573550eb', 'threadId': '17703970573550eb'}
{'id': '177031073928a223', 'threadId': '177031073928a223'}
{'id': '17702de505951773', 'threadId': '17702de505951773'}
{'id': '17702a3e6d1893de', 'threadId': '17702a3e6d1893de'}

How can I get the actual body of a message using this API?

Solution

As stated in the documentation of users.messages.list:

Note that each message resource contains only an id and a threadId. Additional message details can be fetched using the messages.get method.

So basically it is a two step process:

You use list to get the emails in the inbox.
Use get to read information about them.

Which it looks something like:

results = service.users().messages().list(userId='me').execute()
messages = results.get('messages', [])
messages = [service.users().messages().get(userId='me', id=msg['id']).execute() for msg in messages]

Now, if you do that, you will run into problems as this makes the requests 1 by 1. The way of getting multiple messages with one request is using a batch request:

results = service.users().messages().list(userId='me').execute()
message_ids = results.get('messages', [])

messages = []
def add(id, msg, err):
    # id is given because this will not be called in the same order
    if err:
        print(err)
    else:
        messages.append(msg)

batch = service.new_batch_http_request()
for msg in message_ids:
    batch.add(service.users().messages().get(userId='me', id=msg['id']), add)
batch.execute()

One important note about batch requests is that the order in which the callback is called can be different from the order that you started with.

Gmail API: How can I get the message body?

References