@@ -17,6 +17,7 @@
 import json
 import os
 import threading
+from typing import Any, Callable, Dict, Optional
 
 from firebase_admin import credentials
 from firebase_admin.__about__ import __version__
@@ -31,7 +32,8 @@
 _CONFIG_VALID_KEYS = ['databaseAuthVariableOverride', 'databaseURL', 'httpTimeout', 'projectId',
 'storageBucket']
 
-def initialize_app(credential=None, options=None, name=_DEFAULT_APP_NAME):
+
+def initialize_app(credential: Optional[credentials.Base] = None, options: Optional[Dict[str, Any]] = None, name: str = _DEFAULT_APP_NAME) -> "App":
 """Initializes and returns a new App instance.
 
 Creates a new App instance using the specified options
@@ -83,7 +85,7 @@ def initialize_app(credential=None, options=None, name=_DEFAULT_APP_NAME):
 'you call initialize_app().').format(name))
 
 
-def delete_app(app):
+def delete_app(app: "App"):
 """Gracefully deletes an App instance.
 
 Args:
@@ -98,7 +100,7 @@ def delete_app(app):
 with _apps_lock:
 if _apps.get(app.name) is app:
 del _apps[app.name]
-app._cleanup() # pylint: disable=protected-access
+app._cleanup() # pylint: disable=protected-access
 return
 if app.name == _DEFAULT_APP_NAME:
 raise ValueError(
@@ -111,7 +113,7 @@ def delete_app(app):
 'second argument.').format(app.name))
 
 
-def get_app(name=_DEFAULT_APP_NAME):
+def get_app(name: str = _DEFAULT_APP_NAME) -> "App":
 """Retrieves an App instance by name.
 
 Args:
@@ -190,7 +192,7 @@ class App:
 common to all Firebase APIs.
 """
 
-def __init__(self, name, credential, options):
+def __init__(self, name: str, credential: credentials.Base, options: Optional[Dict[str, Any]]):
 """Constructs a new App using the provided name and options.
 
 Args:
@@ -265,7 +267,7 @@ def _lookup_project_id(self):
 App._validate_project_id(self._options.get('projectId'))
 return project_id
 
-def _get_service(self, name, initializer):
+def _get_service(self, name: str, initializer: Callable):
 """Returns the service instance identified by the given name.
 
 Services are functional entities exposed by the Admin SDK (e.g. auth, database). Each
@@ -307,3 +309,5 @@ def _cleanup(self):
 if hasattr(service, 'close') and hasattr(service.close, '__call__'):
 service.close()
 self._services = None
+
+App.update

@@ -15,6 +15,7 @@
 """Internal utilities common to all modules."""
 
 import json
+from typing import Callable, Optional
 
 import google.auth
 import requests
@@ -76,7 +77,7 @@
 }
 
 
-def _get_initialized_app(app):
+def _get_initialized_app(app: Optional[firebase_admin.App]):
 """Returns a reference to an initialized App instance."""
 if app is None:
 return firebase_admin.get_app()
@@ -92,10 +93,9 @@ def _get_initialized_app(app):
 ' firebase_admin.App, but given "{0}".'.format(type(app)))
 
 
-
-def get_app_service(app, name, initializer):
+def get_app_service(app: Optional[firebase_admin.App], name: str, initializer: Callable):
 app = _get_initialized_app(app)
-return app._get_service(name, initializer) # pylint: disable=protected-access
+return app._get_service(name, initializer) # pylint: disable=protected-access
 
 
 def handle_platform_error_from_requests(error, handle_func=None):

@@ -16,11 +16,13 @@
 import collections
 import json
 import pathlib
+from typing import Any, Dict, Union
 
 import google.auth
 from google.auth.transport import requests
 from google.oauth2 import credentials
 from google.oauth2 import service_account
+import google.auth.credentials
 
 
 _request = requests.Request()
@@ -44,7 +46,7 @@
 class Base:
 """Provides OAuth2 access tokens for accessing Firebase services."""
 
-def get_access_token(self):
+def get_access_token(self) -> AccessTokenInfo:
 """Fetches a Google OAuth2 access token using this credential instance.
 
 Returns:
@@ -54,7 +56,7 @@ def get_access_token(self):
 google_cred.refresh(_request)
 return AccessTokenInfo(google_cred.token, google_cred.expiry)
 
-def get_credential(self):
+def get_credential(self) -> google.auth.credentials.Credentials:
 """Returns the Google credential instance used for authentication."""
 raise NotImplementedError
 
@@ -64,7 +66,7 @@ class Certificate(Base):
 
 _CREDENTIAL_TYPE = 'service_account'
 
-def __init__(self, cert):
+def __init__(self, cert: Union[str, Dict[str, Any]]):
 """Initializes a credential from a Google service account certificate.
 
 Service account certificates can be downloaded as JSON files from the Firebase console.
@@ -158,6 +160,7 @@ def _load_credential(self):
 if not self._g_credential:
 self._g_credential, self._project_id = google.auth.default(scopes=_scopes)
 
+
 class RefreshToken(Base):
 """A credential initialized from an existing refresh token."""
 

@@ -19,7 +19,7 @@
 """
 
 try:
-from google.cloud import firestore # pylint: disable=import-error,no-name-in-module
+from google.cloud import firestore # pylint: disable=import-error,no-name-in-module
 existing = globals().keys()
 for key, value in firestore.__dict__.items():
 if not key.startswith('_') and key not in existing:
@@ -28,13 +28,15 @@
 raise ImportError('Failed to import the Cloud Firestore library for Python. Make sure '
 'to install the "google-cloud-firestore" module.')
 
-from firebase_admin import _utils
+from firebase_admin import _utils, App
+import google.auth.credentials
+from typing import Optional
 
 
 _FIRESTORE_ATTRIBUTE = '_firestore'
 
 
-def client(app=None):
+def client(app: Optional[App] = None) -> firestore.Client:
 """Returns a client that can be used to interact with Google Cloud Firestore.
 
 Args:
@@ -57,14 +59,14 @@ def client(app=None):
 class _FirestoreClient:
 """Holds a Google Cloud Firestore client instance."""
 
-def __init__(self, credentials, project):
+def __init__(self, credentials: google.auth.credentials.Credentials, project: str):
 self._client = firestore.Client(credentials=credentials, project=project)
 
-def get(self):
+def get(self) -> firestore.Client:
 return self._client
 
 @classmethod
-def from_app(cls, app):
+def from_app(cls, app: App):
 """Creates a new _FirestoreClient for the specified app."""
 credentials = app.credential.get_credential()
 project = app.project_id

@@ -95,6 +95,7 @@
 def _get_messaging_service(app):
 return _utils.get_app_service(app, _MESSAGING_ATTRIBUTE, _MessagingService)
 
+
 def send(message, dry_run=False, app=None):
 """Sends the given message via Firebase Cloud Messaging (FCM).
 
@@ -115,6 +116,7 @@ def send(message, dry_run=False, app=None):
 """
 return _get_messaging_service(app).send(message, dry_run)
 
+
 def send_all(messages, dry_run=False, app=None):
 """Sends the given list of messages via Firebase Cloud Messaging as a single batch.
 
@@ -135,6 +137,7 @@ def send_all(messages, dry_run=False, app=None):
 """
 return _get_messaging_service(app).send_all(messages, dry_run)
 
+
 def send_multicast(multicast_message, dry_run=False, app=None):
 """Sends the given mutlicast message to all tokens via Firebase Cloud Messaging (FCM).
 
@@ -166,6 +169,7 @@ def send_multicast(multicast_message, dry_run=False, app=None):
 ) for token in multicast_message.tokens]
 return _get_messaging_service(app).send_all(messages, dry_run)
 
+
 def subscribe_to_topic(tokens, topic, app=None):
 """Subscribes a list of registration tokens to an FCM topic.
 
@@ -185,6 +189,7 @@ def subscribe_to_topic(tokens, topic, app=None):
 return _get_messaging_service(app).make_topic_management_request(
 tokens, topic, 'iid/v1:batchAdd')
 
+
 def unsubscribe_from_topic(tokens, topic, app=None):
 """Unsubscribes a list of registration tokens from an FCM topic.
 

@@ -211,13 +211,13 @@ def from_dict(cls, data, app=None):
 tflite_format = TFLiteFormat.from_dict(tflite_format_data)
 model = Model(model_format=tflite_format)
 model._data = data_copy # pylint: disable=protected-access
-model._app = app # pylint: disable=protected-access
+model._app = app # pylint: disable=protected-access
 return model
 
 def _update_from_dict(self, data):
 copy = Model.from_dict(data)
 self.model_format = copy.model_format
-self._data = copy._data # pylint: disable=protected-access
+self._data = copy._data # pylint: disable=protected-access
 
 def __eq__(self, other):
 if isinstance(other, self.__class__):
@@ -334,7 +334,7 @@ def model_format(self):
 def model_format(self, model_format):
 if model_format is not None:
 _validate_model_format(model_format)
-self._model_format = model_format #Can be None
+self._model_format = model_format # Can be None
 return self
 
 def as_dict(self, for_upload=False):
@@ -370,7 +370,7 @@ def from_dict(cls, data):
 """Create an instance of the object from a dict."""
 data_copy = dict(data)
 tflite_format = TFLiteFormat(model_source=cls._init_model_source(data_copy))
-tflite_format._data = data_copy # pylint: disable=protected-access
+tflite_format._data = data_copy # pylint: disable=protected-access
 return tflite_format
 
 def __eq__(self, other):
@@ -405,7 +405,7 @@ def model_source(self, model_source):
 if model_source is not None:
 if not isinstance(model_source, TFLiteModelSource):
 raise TypeError('Model source must be a TFLiteModelSource object.')
-self._model_source = model_source # Can be None
+self._model_source = model_source # Can be None
 
 @property
 def size_bytes(self):
@@ -485,7 +485,7 @@ def __init__(self, gcs_tflite_uri, app=None):
 
 def __eq__(self, other):
 if isinstance(other, self.__class__):
-return self._gcs_tflite_uri == other._gcs_tflite_uri # pylint: disable=protected-access
+return self._gcs_tflite_uri == other._gcs_tflite_uri # pylint: disable=protected-access
 return False
 
 def __ne__(self, other):
@@ -775,7 +775,7 @@ def _validate_display_name(display_name):
 
 def _validate_tags(tags):
 if not isinstance(tags, list) or not \
-all(isinstance(tag, str) for tag in tags):
+all(isinstance(tag, str) for tag in tags):
 raise TypeError('Tags must be a list of strings.')
 if not all(_TAG_PATTERN.match(tag) for tag in tags):
 raise ValueError('Tag format is invalid.')
@@ -789,6 +789,7 @@ def _validate_gcs_tflite_uri(uri):
 raise ValueError('GCS TFLite URI format is invalid.')
 return uri
 
+
 def _validate_auto_ml_model(model):
 if not _AUTO_ML_MODEL_PATTERN.match(model):
 raise ValueError('Model resource name format is invalid.')
@@ -809,7 +810,7 @@ def _validate_list_filter(list_filter):
 
 def _validate_page_size(page_size):
 if page_size is not None:
-if type(page_size) is not int: # pylint: disable=unidiomatic-typecheck
+if type(page_size) is not int: # pylint: disable=unidiomatic-typecheck
 # Specifically type() to disallow boolean which is a subtype of int
 raise TypeError('Page size must be a number or None.')
 if page_size < 1 or page_size > _MAX_PAGE_SIZE:
@@ -864,7 +865,7 @@ def _exponential_backoff(self, current_attempt, stop_time):
 
 if stop_time is not None:
 max_seconds_left = (stop_time - datetime.datetime.now()).total_seconds()
-if max_seconds_left < 1: # allow a bit of time for rpc
+if max_seconds_left < 1: # allow a bit of time for rpc
 raise exceptions.DeadlineExceededError('Polling max time exceeded.')
 wait_time_seconds = min(wait_time_seconds, max_seconds_left - 1)
 time.sleep(wait_time_seconds)
@@ -925,7 +926,6 @@ def handle_operation(self, operation, wait_for_operation=False, max_time_seconds
 # If the operation is not complete or timed out, return a (locked) model instead
 return get_model(model_id).as_dict()
 
-
 def create_model(self, model):
 _validate_model(model)
 try:

@@ -25,12 +25,14 @@
 raise ImportError('Failed to import the Cloud Storage library for Python. Make sure '
 'to install the "google-cloud-storage" module.')
 
-from firebase_admin import _utils
+from firebase_admin import _utils, App
+from typing import Optional
 
 
 _STORAGE_ATTRIBUTE = '_storage'
 
-def bucket(name=None, app=None) -> storage.Bucket:
+
+def bucket(name: Optional[str] = None, app: Optional[App] = None) -> storage.Bucket:
 """Returns a handle to a Google Cloud Storage bucket.
 
 If the name argument is not provided, uses the 'storageBucket' option specified when
@@ -67,7 +69,7 @@ def from_app(cls, app):
 # significantly speeds up the initialization of the storage client.
 return _StorageClient(credentials, app.project_id, default_bucket)
 
-def bucket(self, name=None):
+def bucket(self, name: Optional[str] = None):
 """Returns a handle to the specified Cloud Storage Bucket."""
 bucket_name = name if name is not None else self._default_bucket
 if bucket_name is None:

@@ -183,6 +183,7 @@ def list_tenants(page_token=None, max_results=_MAX_LIST_TENANTS_RESULTS, app=Non
 FirebaseError: If an error occurs while retrieving the user accounts.
 """
 tenant_mgt_service = _get_tenant_mgt_service(app)
+
 def download(page_token, max_results):
 return tenant_mgt_service.list_tenants(page_token, max_results)
 return ListTenantsPage(download, page_token, max_results)
@@ -206,7 +207,7 @@ class Tenant:
 def __init__(self, data):
 if not isinstance(data, dict):
 raise ValueError('Invalid data argument in Tenant constructor: {0}'.format(data))
-if not 'name' in data:
+if 'name' not in data:
 raise ValueError('Tenant response missing required keys.')
 
 self._data = data
@@ -256,7 +257,7 @@ def auth_for_tenant(self, tenant_id):
 
 client = auth.Client(self.app, tenant_id=tenant_id)
 self.tenant_clients[tenant_id] = client
-return client
+return client
 
 def get_tenant(self, tenant_id):
 """Gets the tenant corresponding to the given ``tenant_id``."""