The script implements robust API error handling using Python’s try-except blocks.

1. <item 1> & <item 2>: Establish the error-handling structure to catch exceptions during the network request.
2. <item 3>: Identifies a 401 Unauthorized error, triggering create_dnac_token() to refresh the expired or missing session token.
3. <item 4>: Identifies a 429 Too Many Requests error, initiating a backoff_retry logic to respect rate limits.
4. <item 5>: Completes the HTTP header for Basic Authentication required to request a token.
5. <item 6>: Detects a 5xx Server Error, resulting in a system exit as the service is unreachable.

Cisco DevNet Documentation: DNA Center Platform Intent API - Authentication. This documentation specifies the use of the Authorization: Basic header (matching ) and the receipt of a Token in response to access subsequent APIs.

Python Requests Library (v2.31.0): Status Code Lookup. The requests.codes object provides symbolic names for HTTP status codes, where UNAUTHORIZED is 401, TOO_MANY_REQUESTS is 429, and SERVER_ERROR generally refers to the 500-599 range.

Python Software Foundation: Errors and Exceptions. This defines the syntax for try and except Exception as e (matching and ) used to handle runtime errors in network communication.

RFC 7235: Hypertext Transfer Protocol (HTTP/1.1): Authentication. Section 2.1 defines the Authorization header field used in the create_dnac_token function.

RFC 6585: Additional HTTP Status Codes. Section 4 defines the 429 status code (TOO_MANY_REQUESTS) handled in the backoff logic of the script.