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Diffstat (limited to 'google/api_core/page_iterator.py')
| -rw-r--r-- | google/api_core/page_iterator.py | 571 |
1 files changed, 571 insertions, 0 deletions
diff --git a/google/api_core/page_iterator.py b/google/api_core/page_iterator.py new file mode 100644 index 0000000..7ddc5cb --- /dev/null +++ b/google/api_core/page_iterator.py @@ -0,0 +1,571 @@ +# Copyright 2015 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. + +"""Iterators for paging through paged API methods. + +These iterators simplify the process of paging through API responses +where the request takes a page token and the response is a list of results with +a token for the next page. See `list pagination`_ in the Google API Style Guide +for more details. + +.. _list pagination: + https://cloud.google.com/apis/design/design_patterns#list_pagination + +API clients that have methods that follow the list pagination pattern can +return an :class:`.Iterator`. You can use this iterator to get **all** of +the results across all pages:: + + >>> results_iterator = client.list_resources() + >>> list(results_iterator) # Convert to a list (consumes all values). + +Or you can walk your way through items and call off the search early if +you find what you're looking for (resulting in possibly fewer requests):: + + >>> for resource in results_iterator: + ... print(resource.name) + ... if not resource.is_valid: + ... break + +At any point, you may check the number of items consumed by referencing the +``num_results`` property of the iterator:: + + >>> for my_item in results_iterator: + ... if results_iterator.num_results >= 10: + ... break + +When iterating, not every new item will send a request to the server. +To iterate based on each page of items (where a page corresponds to +a request):: + + >>> for page in results_iterator.pages: + ... print('=' * 20) + ... print(' Page number: {:d}'.format(iterator.page_number)) + ... print(' Items in page: {:d}'.format(page.num_items)) + ... print(' First item: {!r}'.format(next(page))) + ... print('Items remaining: {:d}'.format(page.remaining)) + ... print('Next page token: {}'.format(iterator.next_page_token)) + ==================== + Page number: 1 + Items in page: 1 + First item: <MyItemClass at 0x7f1d3cccf690> + Items remaining: 0 + Next page token: eav1OzQB0OM8rLdGXOEsyQWSG + ==================== + Page number: 2 + Items in page: 19 + First item: <MyItemClass at 0x7f1d3cccffd0> + Items remaining: 18 + Next page token: None + +Then, for each page you can get all the resources on that page by iterating +through it or using :func:`list`:: + + >>> list(page) + [ + <MyItemClass at 0x7fd64a098ad0>, + <MyItemClass at 0x7fd64a098ed0>, + <MyItemClass at 0x7fd64a098e90>, + ] +""" + +import abc + + +class Page(object): + """Single page of results in an iterator. + + Args: + parent (google.api_core.page_iterator.Iterator): The iterator that owns + the current page. + items (Sequence[Any]): An iterable (that also defines __len__) of items + from a raw API response. + item_to_value (Callable[google.api_core.page_iterator.Iterator, Any]): + Callable to convert an item from the type in the raw API response + into the native object. Will be called with the iterator and a + single item. + raw_page Optional[google.protobuf.message.Message]: + The raw page response. + """ + + def __init__(self, parent, items, item_to_value, raw_page=None): + self._parent = parent + self._num_items = len(items) + self._remaining = self._num_items + self._item_iter = iter(items) + self._item_to_value = item_to_value + self._raw_page = raw_page + + @property + def raw_page(self): + """google.protobuf.message.Message""" + return self._raw_page + + @property + def num_items(self): + """int: Total items in the page.""" + return self._num_items + + @property + def remaining(self): + """int: Remaining items in the page.""" + return self._remaining + + def __iter__(self): + """The :class:`Page` is an iterator of items.""" + return self + + def __next__(self): + """Get the next value in the page.""" + item = next(self._item_iter) + result = self._item_to_value(self._parent, item) + # Since we've successfully got the next value from the + # iterator, we update the number of remaining. + self._remaining -= 1 + return result + + +def _item_to_value_identity(iterator, item): + """An item to value transformer that returns the item un-changed.""" + # pylint: disable=unused-argument + # We are conforming to the interface defined by Iterator. + return item + + +class Iterator(object, metaclass=abc.ABCMeta): + """A generic class for iterating through API list responses. + + Args: + client(google.cloud.client.Client): The API client. + item_to_value (Callable[google.api_core.page_iterator.Iterator, Any]): + Callable to convert an item from the type in the raw API response + into the native object. Will be called with the iterator and a + single item. + page_token (str): A token identifying a page in a result set to start + fetching results from. + max_results (int): The maximum number of results to fetch. + """ + + def __init__( + self, + client, + item_to_value=_item_to_value_identity, + page_token=None, + max_results=None, + ): + self._started = False + self.__active_iterator = None + + self.client = client + """Optional[Any]: The client that created this iterator.""" + self.item_to_value = item_to_value + """Callable[Iterator, Any]: Callable to convert an item from the type + in the raw API response into the native object. Will be called with + the iterator and a + single item. + """ + self.max_results = max_results + """int: The maximum number of results to fetch""" + + # The attributes below will change over the life of the iterator. + self.page_number = 0 + """int: The current page of results.""" + self.next_page_token = page_token + """str: The token for the next page of results. If this is set before + the iterator starts, it effectively offsets the iterator to a + specific starting point.""" + self.num_results = 0 + """int: The total number of results fetched so far.""" + + @property + def pages(self): + """Iterator of pages in the response. + + returns: + types.GeneratorType[google.api_core.page_iterator.Page]: A + generator of page instances. + + raises: + ValueError: If the iterator has already been started. + """ + if self._started: + raise ValueError("Iterator has already started", self) + self._started = True + return self._page_iter(increment=True) + + def _items_iter(self): + """Iterator for each item returned.""" + for page in self._page_iter(increment=False): + for item in page: + self.num_results += 1 + yield item + + def __iter__(self): + """Iterator for each item returned. + + Returns: + types.GeneratorType[Any]: A generator of items from the API. + + Raises: + ValueError: If the iterator has already been started. + """ + if self._started: + raise ValueError("Iterator has already started", self) + self._started = True + return self._items_iter() + + def __next__(self): + if self.__active_iterator is None: + self.__active_iterator = iter(self) + return next(self.__active_iterator) + + def _page_iter(self, increment): + """Generator of pages of API responses. + + Args: + increment (bool): Flag indicating if the total number of results + should be incremented on each page. This is useful since a page + iterator will want to increment by results per page while an + items iterator will want to increment per item. + + Yields: + Page: each page of items from the API. + """ + page = self._next_page() + while page is not None: + self.page_number += 1 + if increment: + self.num_results += page.num_items + yield page + page = self._next_page() + + @abc.abstractmethod + def _next_page(self): + """Get the next page in the iterator. + + This does nothing and is intended to be over-ridden by subclasses + to return the next :class:`Page`. + + Raises: + NotImplementedError: Always, this method is abstract. + """ + raise NotImplementedError + + +def _do_nothing_page_start(iterator, page, response): + """Helper to provide custom behavior after a :class:`Page` is started. + + This is a do-nothing stand-in as the default value. + + Args: + iterator (Iterator): An iterator that holds some request info. + page (Page): The page that was just created. + response (Any): The API response for a page. + """ + # pylint: disable=unused-argument + pass + + +class HTTPIterator(Iterator): + """A generic class for iterating through HTTP/JSON API list responses. + + To make an iterator work, you'll need to provide a way to convert a JSON + item returned from the API into the object of your choice (via + ``item_to_value``). You also may need to specify a custom ``items_key`` so + that a given response (containing a page of results) can be parsed into an + iterable page of the actual objects you want. + + Args: + client (google.cloud.client.Client): The API client. + api_request (Callable): The function to use to make API requests. + Generally, this will be + :meth:`google.cloud._http.JSONConnection.api_request`. + path (str): The method path to query for the list of items. + item_to_value (Callable[google.api_core.page_iterator.Iterator, Any]): + Callable to convert an item from the type in the JSON response into + a native object. Will be called with the iterator and a single + item. + items_key (str): The key in the API response where the list of items + can be found. + page_token (str): A token identifying a page in a result set to start + fetching results from. + page_size (int): The maximum number of results to fetch per page + max_results (int): The maximum number of results to fetch + extra_params (dict): Extra query string parameters for the + API call. + page_start (Callable[ + google.api_core.page_iterator.Iterator, + google.api_core.page_iterator.Page, dict]): Callable to provide + any special behavior after a new page has been created. Assumed + signature takes the :class:`.Iterator` that started the page, + the :class:`.Page` that was started and the dictionary containing + the page response. + next_token (str): The name of the field used in the response for page + tokens. + + .. autoattribute:: pages + """ + + _DEFAULT_ITEMS_KEY = "items" + _PAGE_TOKEN = "pageToken" + _MAX_RESULTS = "maxResults" + _NEXT_TOKEN = "nextPageToken" + _RESERVED_PARAMS = frozenset([_PAGE_TOKEN]) + _HTTP_METHOD = "GET" + + def __init__( + self, + client, + api_request, + path, + item_to_value, + items_key=_DEFAULT_ITEMS_KEY, + page_token=None, + page_size=None, + max_results=None, + extra_params=None, + page_start=_do_nothing_page_start, + next_token=_NEXT_TOKEN, + ): + super(HTTPIterator, self).__init__( + client, item_to_value, page_token=page_token, max_results=max_results + ) + self.api_request = api_request + self.path = path + self._items_key = items_key + self.extra_params = extra_params + self._page_size = page_size + self._page_start = page_start + self._next_token = next_token + # Verify inputs / provide defaults. + if self.extra_params is None: + self.extra_params = {} + self._verify_params() + + def _verify_params(self): + """Verifies the parameters don't use any reserved parameter. + + Raises: + ValueError: If a reserved parameter is used. + """ + reserved_in_use = self._RESERVED_PARAMS.intersection(self.extra_params) + if reserved_in_use: + raise ValueError("Using a reserved parameter", reserved_in_use) + + def _next_page(self): + """Get the next page in the iterator. + + Returns: + Optional[Page]: The next page in the iterator or :data:`None` if + there are no pages left. + """ + if self._has_next_page(): + response = self._get_next_page_response() + items = response.get(self._items_key, ()) + page = Page(self, items, self.item_to_value, raw_page=response) + self._page_start(self, page, response) + self.next_page_token = response.get(self._next_token) + return page + else: + return None + + def _has_next_page(self): + """Determines whether or not there are more pages with results. + + Returns: + bool: Whether the iterator has more pages. + """ + if self.page_number == 0: + return True + + if self.max_results is not None: + if self.num_results >= self.max_results: + return False + + return self.next_page_token is not None + + def _get_query_params(self): + """Getter for query parameters for the next request. + + Returns: + dict: A dictionary of query parameters. + """ + result = {} + if self.next_page_token is not None: + result[self._PAGE_TOKEN] = self.next_page_token + + page_size = None + if self.max_results is not None: + page_size = self.max_results - self.num_results + if self._page_size is not None: + page_size = min(page_size, self._page_size) + elif self._page_size is not None: + page_size = self._page_size + + if page_size is not None: + result[self._MAX_RESULTS] = page_size + + result.update(self.extra_params) + return result + + def _get_next_page_response(self): + """Requests the next page from the path provided. + + Returns: + dict: The parsed JSON response of the next page's contents. + + Raises: + ValueError: If the HTTP method is not ``GET`` or ``POST``. + """ + params = self._get_query_params() + if self._HTTP_METHOD == "GET": + return self.api_request( + method=self._HTTP_METHOD, path=self.path, query_params=params + ) + elif self._HTTP_METHOD == "POST": + return self.api_request( + method=self._HTTP_METHOD, path=self.path, data=params + ) + else: + raise ValueError("Unexpected HTTP method", self._HTTP_METHOD) + + +class _GAXIterator(Iterator): + """A generic class for iterating through Cloud gRPC APIs list responses. + + Any: + client (google.cloud.client.Client): The API client. + page_iter (google.gax.PageIterator): A GAX page iterator to be wrapped + to conform to the :class:`Iterator` interface. + item_to_value (Callable[Iterator, Any]): Callable to convert an item + from the the protobuf response into a native object. Will + be called with the iterator and a single item. + max_results (int): The maximum number of results to fetch. + + .. autoattribute:: pages + """ + + def __init__(self, client, page_iter, item_to_value, max_results=None): + super(_GAXIterator, self).__init__( + client, + item_to_value, + page_token=page_iter.page_token, + max_results=max_results, + ) + self._gax_page_iter = page_iter + + def _next_page(self): + """Get the next page in the iterator. + + Wraps the response from the :class:`~google.gax.PageIterator` in a + :class:`Page` instance and captures some state at each page. + + Returns: + Optional[Page]: The next page in the iterator or :data:`None` if + there are no pages left. + """ + try: + items = next(self._gax_page_iter) + page = Page(self, items, self.item_to_value) + self.next_page_token = self._gax_page_iter.page_token or None + return page + except StopIteration: + return None + + +class GRPCIterator(Iterator): + """A generic class for iterating through gRPC list responses. + + .. note:: The class does not take a ``page_token`` argument because it can + just be specified in the ``request``. + + Args: + client (google.cloud.client.Client): The API client. This unused by + this class, but kept to satisfy the :class:`Iterator` interface. + method (Callable[protobuf.Message]): A bound gRPC method that should + take a single message for the request. + request (protobuf.Message): The request message. + items_field (str): The field in the response message that has the + items for the page. + item_to_value (Callable[GRPCIterator, Any]): Callable to convert an + item from the type in the JSON response into a native object. Will + be called with the iterator and a single item. + request_token_field (str): The field in the request message used to + specify the page token. + response_token_field (str): The field in the response message that has + the token for the next page. + max_results (int): The maximum number of results to fetch. + + .. autoattribute:: pages + """ + + _DEFAULT_REQUEST_TOKEN_FIELD = "page_token" + _DEFAULT_RESPONSE_TOKEN_FIELD = "next_page_token" + + def __init__( + self, + client, + method, + request, + items_field, + item_to_value=_item_to_value_identity, + request_token_field=_DEFAULT_REQUEST_TOKEN_FIELD, + response_token_field=_DEFAULT_RESPONSE_TOKEN_FIELD, + max_results=None, + ): + super(GRPCIterator, self).__init__( + client, item_to_value, max_results=max_results + ) + self._method = method + self._request = request + self._items_field = items_field + self._request_token_field = request_token_field + self._response_token_field = response_token_field + + def _next_page(self): + """Get the next page in the iterator. + + Returns: + Page: The next page in the iterator or :data:`None` if + there are no pages left. + """ + if not self._has_next_page(): + return None + + if self.next_page_token is not None: + setattr(self._request, self._request_token_field, self.next_page_token) + + response = self._method(self._request) + + self.next_page_token = getattr(response, self._response_token_field) + items = getattr(response, self._items_field) + page = Page(self, items, self.item_to_value, raw_page=response) + + return page + + def _has_next_page(self): + """Determines whether or not there are more pages with results. + + Returns: + bool: Whether the iterator has more pages. + """ + if self.page_number == 0: + return True + + if self.max_results is not None: + if self.num_results >= self.max_results: + return False + + # Note: intentionally a falsy check instead of a None check. The RPC + # can return an empty string indicating no more pages. + return True if self.next_page_token else False |