feat: Gmail list messages (#2238)

Author: vinay-google

gmail/snippet/list_messages.py

@@ -0,0 +1,76 @@
+# Copyright 2025 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_list_messages]
+import os.path
+from google.auth.transport.requests import Request
+from google.oauth2.credentials import Credentials
+from google_auth_oauthlib.flow import InstalledAppFlow
+from googleapiclient.discovery import build
+from googleapiclient.errors import HttpError
+
+# 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 messages.
+    """
+    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())
+
+    try:
+        # Call the Gmail API
+        service = build("gmail", "v1", credentials=creds)
+        results = (
+            service.users().messages().list(userId="me", labelIds=["INBOX"]).execute()
+        )
+        messages = results.get("messages", [])
+
+        if not messages:
+            print("No messages found.")
+            return
+
+        print("Messages:")
+        for message in messages:
+            print(f'Message ID: {message["id"]}')
+            msg = (
+                service.users().messages().get(userId="me", id=message["id"]).execute()
+            )
+            print(f'  Subject: {msg["snippet"]}')
+
+    except HttpError as error:
+        # TODO(developer) - Handle errors from gmail API.
+        print(f"An error occurred: {error}")
+
+
+if __name__ == "__main__":
+    main()
+
+# [END gmail_list_messages]