DynamoDB.Table.scan(**kwargs)¶The Scan operation returns one or more items and item attributes by accessing every item in a table or a secondary index. To have DynamoDB return fewer items, you can provide a FilterExpression operation.
If the total number of scanned items exceeds the maximum dataset size limit of 1 MB, the scan stops and results are returned to the user as a LastEvaluatedKey value to continue the scan in a subsequent operation. The results also include the number of items exceeding the limit. A scan can result in no table data meeting the filter criteria.
A single Scan operation reads up to the maximum number of items set (if using the Limit parameter) or a maximum of 1 MB of data and then apply any filtering to the results using FilterExpression . If LastEvaluatedKey is present in the response, you need to paginate the result set. For more information, see Paginating the Results in the Amazon DynamoDB Developer Guide .
Scanoperations proceed sequentially; however, for faster performance on a large table or secondary index, applications can request a parallelScanoperation by providing theSegmentandTotalSegmentsparameters. For more information, see Parallel Scan in the Amazon DynamoDB Developer Guide .
Scanuses eventually consistent reads when accessing the data in a table; therefore, the result set might not include the changes to data in the table immediately before the operation began. If you need a consistent copy of the data, as of the time that theScanbegins, you can set theConsistentReadparameter totrue.
See also: AWS API Documentation
Request Syntax
response = table.scan(
IndexName='string',
AttributesToGet=[
'string',
],
Limit=123,
Select='ALL_ATTRIBUTES'|'ALL_PROJECTED_ATTRIBUTES'|'SPECIFIC_ATTRIBUTES'|'COUNT',
ScanFilter={
'string': {
'AttributeValueList': [
'string'|123|Binary(b'bytes')|True|None|set(['string'])|set([123])|set([Binary(b'bytes')])|[]|{},
],
'ComparisonOperator': 'EQ'|'NE'|'IN'|'LE'|'LT'|'GE'|'GT'|'BETWEEN'|'NOT_NULL'|'NULL'|'CONTAINS'|'NOT_CONTAINS'|'BEGINS_WITH'
}
},
ConditionalOperator='AND'|'OR',
ExclusiveStartKey={
'string': 'string'|123|Binary(b'bytes')|True|None|set(['string'])|set([123])|set([Binary(b'bytes')])|[]|{}
},
ReturnConsumedCapacity='INDEXES'|'TOTAL'|'NONE',
TotalSegments=123,
Segment=123,
ProjectionExpression='string',
FilterExpression=Attr('myattribute').eq('myvalue'),
ExpressionAttributeNames={
'string': 'string'
},
ExpressionAttributeValues={
'string': 'string'|123|Binary(b'bytes')|True|None|set(['string'])|set([123])|set([Binary(b'bytes')])|[]|{}
},
ConsistentRead=True|False
)
IndexName parameter, you must also provide TableName .This is a legacy parameter. Use ProjectionExpression instead. For more information, see AttributesToGet in the Amazon DynamoDB Developer Guide .
LastEvaluatedKey to apply in a subsequent operation, so that you can pick up where you left off. Also, if the processed dataset size exceeds 1 MB before DynamoDB reaches this limit, it stops the operation and returns the matching values up to the limit, and a key in LastEvaluatedKey to apply in a subsequent operation to continue the operation. For more information, see Working with Queries in the Amazon DynamoDB Developer Guide .The attributes to be returned in the result. You can retrieve all item attributes, specific item attributes, the count of matching items, or in the case of an index, some or all of the attributes projected into the index.
ALL_ATTRIBUTES - Returns all of the item attributes from the specified table or index. If you query a local secondary index, then for each matching item in the index, DynamoDB fetches the entire item from the parent table. If the index is configured to project all item attributes, then all of the data can be obtained from the local secondary index, and no fetching is required.ALL_PROJECTED_ATTRIBUTES - Allowed only when querying an index. Retrieves all attributes that have been projected into the index. If the index is configured to project all attributes, this return value is equivalent to specifying ALL_ATTRIBUTES .COUNT - Returns the number of matching items, rather than the matching items themselves. Note that this uses the same quantity of read capacity units as getting the items, and is subject to the same item size calculations.SPECIFIC_ATTRIBUTES - Returns only the attributes listed in ProjectionExpression . This return value is equivalent to specifying ProjectionExpression without specifying any value for Select . If you query or scan a local secondary index and request only attributes that are projected into that index, the operation reads only the index and not the table. If any of the requested attributes are not projected into the local secondary index, DynamoDB fetches each of these attributes from the parent table. This extra fetching incurs additional throughput cost and latency. If you query or scan a global secondary index, you can only request attributes that are projected into the index. Global secondary index queries cannot fetch attributes from the parent table.If neither Select nor ProjectionExpression are specified, DynamoDB defaults to ALL_ATTRIBUTES when accessing a table, and ALL_PROJECTED_ATTRIBUTES when accessing an index. You cannot use both Select and ProjectionExpression together in a single request, unless the value for Select is SPECIFIC_ATTRIBUTES . (This usage is equivalent to specifying ProjectionExpression without any value for Select .)
Note
If you use the ProjectionExpression parameter, then the value for Select can only be SPECIFIC_ATTRIBUTES . Any other value for Select will return an error.
This is a legacy parameter. Use FilterExpression instead. For more information, see ScanFilter in the Amazon DynamoDB Developer Guide .
Represents the selection criteria for a Query or Scan operation:
Query operation, Condition is used for specifying the KeyConditions to use when querying a table or an index. For KeyConditions , only the following comparison operators are supported: EQ | LE | LT | GE | GT | BEGINS_WITH | BETWEEN Condition is also used in a QueryFilter , which evaluates the query results and returns only the desired values.Scan operation, Condition is used in a ScanFilter , which evaluates the scan results and returns only the desired values.One or more values to evaluate against the supplied attribute. The number of values in the list depends on the ComparisonOperator being used.
For type Number, value comparisons are numeric.
String value comparisons for greater than, equals, or less than are based on ASCII character code values. For example, a is greater than A , and a is greater than B . For a list of code values, see http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters.
For Binary, DynamoDB treats each byte of the binary data as unsigned when it compares binary values.
A comparator for evaluating attributes. For example, equals, greater than, less than, etc.
The following comparison operators are available:
EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN
The following are descriptions of each comparison operator.
EQ : Equal. EQ is supported for all data types, including lists and maps. AttributeValueList can contain only one AttributeValue element of type String, Number, Binary, String Set, Number Set, or Binary Set. If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"} . Also, {"N":"6"} does not equal {"NS":["6", "2", "1"]} .NE : Not equal. NE is supported for all data types, including lists and maps. AttributeValueList can contain only one AttributeValue of type String, Number, Binary, String Set, Number Set, or Binary Set. If an item contains an AttributeValue of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"} . Also, {"N":"6"} does not equal {"NS":["6", "2", "1"]} .LE : Less than or equal. AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"} . Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]} .LT : Less than. AttributeValueList can contain only one AttributeValue of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"} . Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]} .GE : Greater than or equal. AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"} . Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]} .GT : Greater than. AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not equal {"N":"6"} . Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]} .NOT_NULL : The attribute exists. NOT_NULL is supported for all data types, including lists and maps.Note
This operator tests for the existence of an attribute, not its data type. If the data type of attribute " a " is null, and you evaluate it using NOT_NULL , the result is a Boolean true . This result is because the attribute " a " exists; its data type is not relevant to the NOT_NULL comparison operator.
NULL : The attribute does not exist. NULL is supported for all data types, including lists and maps.Note
This operator tests for the nonexistence of an attribute, not its data type. If the data type of attribute " a " is null, and you evaluate it using NULL , the result is a Boolean false . This is because the attribute " a " exists; its data type is not relevant to the NULL comparison operator.
CONTAINS : Checks for a subsequence, or value in a set. AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If the target attribute of the comparison is of type String, then the operator checks for a substring match. If the target attribute of the comparison is of type Binary, then the operator looks for a subsequence of the target that matches the input. If the target attribute of the comparison is a set (" SS ", " NS ", or " BS "), then the operator evaluates to true if it finds an exact match with any member of the set. CONTAINS is supported for lists: When evaluating " a CONTAINS b ", " a " can be a list; however, " b " cannot be a set, a map, or a list.NOT_CONTAINS : Checks for absence of a subsequence, or absence of a value in a set. AttributeValueList can contain only one AttributeValue element of type String, Number, or Binary (not a set type). If the target attribute of the comparison is a String, then the operator checks for the absence of a substring match. If the target attribute of the comparison is Binary, then the operator checks for the absence of a subsequence of the target that matches the input. If the target attribute of the comparison is a set (" SS ", " NS ", or " BS "), then the operator evaluates to true if it does not find an exact match with any member of the set. NOT_CONTAINS is supported for lists: When evaluating " a NOT CONTAINS b ", " a " can be a list; however, " b " cannot be a set, a map, or a list.BEGINS_WITH : Checks for a prefix. AttributeValueList can contain only one AttributeValue of type String or Binary (not a Number or a set type). The target attribute of the comparison must be of type String or Binary (not a Number or a set type).IN : Checks for matching elements in a list. AttributeValueList can contain one or more AttributeValue elements of type String, Number, or Binary. These attributes are compared against an existing attribute of an item. If any elements of the input are equal to the item attribute, the expression evaluates to true.BETWEEN : Greater than or equal to the first value, and less than or equal to the second value. AttributeValueList must contain two AttributeValue elements of the same type, either String, Number, or Binary (not a set type). A target attribute matches if the target value is greater than, or equal to, the first element and less than, or equal to, the second element. If an item contains an AttributeValue element of a different type than the one provided in the request, the value does not match. For example, {"S":"6"} does not compare to {"N":"6"} . Also, {"N":"6"} does not compare to {"NS":["6", "2", "1"]}For usage examples of AttributeValueList and ComparisonOperator , see Legacy Conditional Parameters in the Amazon DynamoDB Developer Guide .
FilterExpression instead. For more information, see ConditionalOperator in the Amazon DynamoDB Developer Guide .The primary key of the first item that this operation will evaluate. Use the value that was returned for LastEvaluatedKey in the previous operation.
The data type for ExclusiveStartKey must be String, Number or Binary. No set data types are allowed.
In a parallel scan, a Scan request that includes ExclusiveStartKey must specify the same segment whose previous Scan returned the corresponding value of LastEvaluatedKey .
Determines the level of detail about either provisioned or on-demand throughput consumption that is returned in the response:
INDEXES - The response includes the aggregate ConsumedCapacity for the operation, together with ConsumedCapacity for each table and secondary index that was accessed. Note that some operations, such as GetItem and BatchGetItem , do not access any indexes at all. In these cases, specifying INDEXES will only return ConsumedCapacity information for table(s).TOTAL - The response includes only the aggregate ConsumedCapacity for the operation.NONE - No ConsumedCapacity details are included in the response.For a parallel Scan request, TotalSegments represents the total number of segments into which the Scan operation will be divided. The value of TotalSegments corresponds to the number of application workers that will perform the parallel scan. For example, if you want to use four application threads to scan a table or an index, specify a TotalSegments value of 4.
The value for TotalSegments must be greater than or equal to 1, and less than or equal to 1000000. If you specify a TotalSegments value of 1, the Scan operation will be sequential rather than parallel.
If you specify TotalSegments , you must also specify Segment .
For a parallel Scan request, Segment identifies an individual segment to be scanned by an application worker.
Segment IDs are zero-based, so the first segment is always 0. For example, if you want to use four application threads to scan a table or an index, then the first thread specifies a Segment value of 0, the second thread specifies 1, and so on.
The value of LastEvaluatedKey returned from a parallel Scan request must be used as ExclusiveStartKey with the same segment ID in a subsequent Scan operation.
The value for Segment must be greater than or equal to 0, and less than the value provided for TotalSegments .
If you provide Segment , you must also provide TotalSegments .
A string that identifies one or more attributes to retrieve from the specified table or index. These attributes can include scalars, sets, or elements of a JSON document. The attributes in the expression must be separated by commas.
If no attribute names are specified, then all attributes will be returned. If any of the requested attributes are not found, they will not appear in the result.
For more information, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide .
boto3.dynamodb.conditions.Attr method) -- The condition(s) an attribute(s) must meet. Valid conditions are listed in the DynamoDB Reference Guide.One or more substitution tokens for attribute names in an expression. The following are some use cases for using ExpressionAttributeNames :
Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:
PercentileThe name of this attribute conflicts with a reserved word, so it cannot be used directly in an expression. (For the complete list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide ). To work around this, you could specify the following for ExpressionAttributeNames :
{"#P":"Percentile"}You could then use this substitution in an expression, as in this example:
#P = :valNote
Tokens that begin with the : character are expression attribute values , which are placeholders for the actual value at runtime.
For more information on expression attribute names, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide .
One or more values that can be substituted in an expression.
Use the : (colon) character in an expression to dereference an attribute value. For example, suppose that you wanted to check whether the value of the ProductStatus attribute was one of the following:
Available | Backordered | Discontinued
You would first need to specify ExpressionAttributeValues as follows:
{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"}, ":disc":{"S":"Discontinued"} }
You could then use these values in an expression, such as this:
ProductStatus IN (:avail, :back, :disc)
For more information on expression attribute values, see Condition Expressions in the Amazon DynamoDB Developer Guide .
A Boolean value that determines the read consistency model during the scan:
ConsistentRead is false , then the data returned from Scan might not contain the results from other recently completed write operations ( PutItem , UpdateItem , or DeleteItem ).ConsistentRead is true , then all of the write operations that completed before the Scan began are guaranteed to be contained in the Scan response.The default setting for ConsistentRead is false .
The ConsistentRead parameter is not supported on global secondary indexes. If you scan a global secondary index with ConsistentRead set to true, you will receive a ValidationException .
dict
Response Syntax
{
'Items': [
{
'string': 'string'|123|Binary(b'bytes')|True|None|set(['string'])|set([123])|set([Binary(b'bytes')])|[]|{}
},
],
'Count': 123,
'ScannedCount': 123,
'LastEvaluatedKey': {
'string': 'string'|123|Binary(b'bytes')|True|None|set(['string'])|set([123])|set([Binary(b'bytes')])|[]|{}
},
'ConsumedCapacity': {
'TableName': 'string',
'CapacityUnits': 123.0,
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'Table': {
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'CapacityUnits': 123.0
},
'LocalSecondaryIndexes': {
'string': {
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'CapacityUnits': 123.0
}
},
'GlobalSecondaryIndexes': {
'string': {
'ReadCapacityUnits': 123.0,
'WriteCapacityUnits': 123.0,
'CapacityUnits': 123.0
}
}
}
}
Response Structure
(dict) --
Represents the output of a Scan operation.
Items (list) --
An array of item attributes that match the scan criteria. Each element in this array consists of an attribute name and the value for that attribute.
Count (integer) --
The number of items in the response.
If you set ScanFilter in the request, then Count is the number of items returned after the filter was applied, and ScannedCount is the number of matching items before the filter was applied.
If you did not use a filter in the request, then Count is the same as ScannedCount .
ScannedCount (integer) --
The number of items evaluated, before any ScanFilter is applied. A high ScannedCount value with few, or no, Count results indicates an inefficient Scan operation. For more information, see Count and ScannedCount in the Amazon DynamoDB Developer Guide .
If you did not use a filter in the request, then ScannedCount is the same as Count .
LastEvaluatedKey (dict) --
The primary key of the item where the operation stopped, inclusive of the previous result set. Use this value to start a new operation, excluding this value in the new request.
If LastEvaluatedKey is empty, then the "last page" of results has been processed and there is no more data to be retrieved.
If LastEvaluatedKey is not empty, it does not necessarily mean that there is more data in the result set. The only way to know when you have reached the end of the result set is when LastEvaluatedKey is empty.
ConsumedCapacity (dict) --
The capacity units consumed by the Scan operation. The data returned includes the total provisioned throughput consumed, along with statistics for the table and any indexes involved in the operation. ConsumedCapacity is only returned if the ReturnConsumedCapacity parameter was specified. For more information, see Provisioned Throughput in the Amazon DynamoDB Developer Guide .
TableName (string) --
The name of the table that was affected by the operation.
CapacityUnits (float) --
The total number of capacity units consumed by the operation.
ReadCapacityUnits (float) --
The total number of read capacity units consumed by the operation.
WriteCapacityUnits (float) --
The total number of write capacity units consumed by the operation.
Table (dict) --
The amount of throughput consumed on the table affected by the operation.
ReadCapacityUnits (float) --
The total number of read capacity units consumed on a table or an index.
WriteCapacityUnits (float) --
The total number of write capacity units consumed on a table or an index.
CapacityUnits (float) --
The total number of capacity units consumed on a table or an index.
LocalSecondaryIndexes (dict) --
The amount of throughput consumed on each local index affected by the operation.
(string) --
(dict) --
Represents the amount of provisioned throughput capacity consumed on a table or an index.
ReadCapacityUnits (float) --
The total number of read capacity units consumed on a table or an index.
WriteCapacityUnits (float) --
The total number of write capacity units consumed on a table or an index.
CapacityUnits (float) --
The total number of capacity units consumed on a table or an index.
GlobalSecondaryIndexes (dict) --
The amount of throughput consumed on each global index affected by the operation.
(string) --
(dict) --
Represents the amount of provisioned throughput capacity consumed on a table or an index.
ReadCapacityUnits (float) --
The total number of read capacity units consumed on a table or an index.
WriteCapacityUnits (float) --
The total number of write capacity units consumed on a table or an index.
CapacityUnits (float) --
The total number of capacity units consumed on a table or an index.