1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
|
# Copyright 2020 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.
"""AsyncIO 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:`.AsyncIterator`:
>>> results_iterator = await client.list_resources()
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)::
>>> async 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::
>>> async 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)::
>>> async 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
"""
import abc
from google.api_core.page_iterator import Page
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 AsyncIterator(abc.ABC):
"""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_async.AsyncIterator, 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_aiterator = 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_aiter(increment=True)
async def _items_aiter(self):
"""Iterator for each item returned."""
async for page in self._page_aiter(increment=False):
for item in page:
self.num_results += 1
yield item
def __aiter__(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_aiter()
async def __anext__(self):
if self.__active_aiterator is None:
self.__active_aiterator = self.__aiter__()
return await self.__active_aiterator.__anext__()
async def _page_aiter(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 = await self._next_page()
while page is not None:
self.page_number += 1
if increment:
self.num_results += page.num_items
yield page
page = await self._next_page()
@abc.abstractmethod
async 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
class AsyncGRPCIterator(AsyncIterator):
"""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().__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
async 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 = await 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
# Note: intentionally a falsy check instead of a None check. The RPC
# can return an empty string indicating no more pages.
if self.max_results is not None:
if self.num_results >= self.max_results:
return False
return True if self.next_page_token else False
|