import boto

s3 = boto.connect_s3("your aws_access_key_id", " your aws_secret_access_key)
bucket = s3.get_bucket("your aws bucket name")
original_key = bucket.get_key("your aws key name")
if original_key:
   signed_url = original_key.generate_url(expires_in=300, query_auth=True, force_http=True)