How do I conditionally insert an item into a dynamodb table using boto3

The documentation for this unfortunately isn't super clear. I needed to accomplish something similar, and here's what worked for me, using boto3:

try:    table.put_item(        Item={            'foo':1,            'bar':2,        },        ConditionExpression='attribute_not_exists(foo) AND attribute_not_exists(bar)'    )except botocore.exceptions.ClientError as e:    # Ignore the ConditionalCheckFailedException, bubble up    # other exceptions.    if e.response['Error']['Code'] != 'ConditionalCheckFailedException':        raise

Similar to the other answer, the key is in the attribute_not_exists function, but it was unclear to me initially how to get that to work. After some experimentation, I was able to get it going with the above.

You dont need the sortkey( or range key) just the partition key or hash key is enough.

try:    table.put_item(        Item={            'foo':1,            'bar':2,        },        ConditionExpression='attribute_not_exists(foo)'    )except botocore.exceptions.ClientError as e:    # Ignore the ConditionalCheckFailedException, bubble up    # other exceptions.    if e.response['Error']['Code'] != 'ConditionalCheckFailedException':        raise

i think that you will get better documentation using client.put_item rather than table.put_item

from boto3 documentation:

To prevent a new item from replacing an existing item, use a conditional expression that contains the attribute_not_exists function with the name of the attribute being used as the partition key for the table. Since every record must contain that attribute, the attribute_not_exists function will only succeed if no matching item exists.

ConditionExpression:

ConditionExpression (string) -- A condition that must be satisfied in order for a conditional PutItem operation to succeed.

An expression can contain any of the following:

Functions: attribute_exists | attribute_not_exists | attribute_type | contains | begins_with | size These function names are case-sensitive.

i am using dynamodb2 overwrite parameter on item.save()