Paginators#
Some AWS operations return results that are incomplete and require subsequent
requests in order to attain the entire result set. The process of sending
subsequent requests to continue where a previous request left off is called
pagination. For example, the list_objects
operation of Amazon S3
returns up to 1000 objects at a time, and you must send subsequent requests
with the appropriate Marker
in order to retrieve the next page of
results.
Paginators are a feature of boto3 that act as an abstraction over the process of iterating over an entire result set of a truncated API operation.
Creating paginators#
Paginators are created via the get_paginator()
method of a boto3
client. The get_paginator()
method accepts an operation name and returns
a reusable Paginator
object. You then call the paginate
method of the
Paginator, passing in any relevant operation parameters to apply to the
underlying API operation. The paginate
method then returns an iterable
PageIterator
:
import boto3
# Create a client
client = boto3.client('s3', region_name='us-west-2')
# Create a reusable Paginator
paginator = client.get_paginator('list_objects_v2')
# Create a PageIterator from the Paginator
page_iterator = paginator.paginate(Bucket='my-bucket')
for page in page_iterator:
print(page['Contents'])
Customizing page iterators#
You must call the paginate
method of a Paginator in order to iterate over
the pages of API operation results. The paginate
method accepts a
PaginationConfig
named argument that can be used to customize the
pagination:
paginator = client.get_paginator('list_objects_v2')
page_iterator = paginator.paginate(Bucket='my-bucket',
PaginationConfig={'MaxItems': 10})
MaxItems
Limits the maximum number of total returned items returned while paginating.
StartingToken
Can be used to modify the starting marker or token of a paginator. This argument if useful for resuming pagination from a previous token or starting pagination at a known position.
PageSize
Controls the number of items returned per page of each result.
Note
Services may choose to return more or fewer items than specified in the
PageSize
argument depending on the service, the operation, or the resource you are paginating.
Filtering results#
Many Paginators can be filtered server-side with options that are passed
through to each underlying API call. For example,
S3.Paginator.list_objects.paginate()
accepts a Prefix
parameter
used to filter the paginated results by prefix server-side before sending them
to the client:
import boto3
client = boto3.client('s3', region_name='us-west-2')
paginator = client.get_paginator('list_objects_v2')
operation_parameters = {'Bucket': 'my-bucket',
'Prefix': 'foo/baz'}
page_iterator = paginator.paginate(**operation_parameters)
for page in page_iterator:
print(page['Contents'])
Filtering results with JMESPath#
JMESPath is a query language for JSON that can be used
directly on paginated results. You can filter results client-side using
JMESPath expressions that are applied to each page of results through the
search
method of a PageIterator
.
import boto3
client = boto3.client('s3', region_name='us-west-2')
paginator = client.get_paginator('list_objects_v2')
page_iterator = paginator.paginate(Bucket='my-bucket')
filtered_iterator = page_iterator.search("Contents[?Size > `100`][]")
for key_data in filtered_iterator:
print(key_data)
When filtering with JMESPath expressions, each page of results that is yielded
by the paginator is mapped through the JMESPath expression. If a JMESPath
expression returns a single value that is not an array, that value is yielded
directly. If the result of applying the JMESPath expression to a page of
results is a list, then each value of the list is yielded individually
(essentially implementing a flat map). For example, in the above expression,
each key that has a Size
greater than 100 is yielded by the
filtered_iterator
.