Question

I want to create a list (not implying Python List) of error messages and corresponding error codes. I have two requirements – be able to look up the error message given an error code and be able to perform the opposite look-up.

1. Is there a native python data type that can achieve this? If not, how should I implement this?
2. This list of error messages + codes would be used by BusinessRuleViolation, a custom exception class. I want this list to associate with BusinessRuleViolation and shouldn’t be modified during runtime. How can I do that?

Answer 1

Typically you’d do this with a pair of dicts – one mapping error codes to messages, and then another one (often programmatically generated) with the reverse mapping.

error_codes_to_messages = {
   1: 'foo',
   2: 'bar',
   3: 'baz',
}

error_messages_to_codes = dict(
    (v,k) for k,v in error_codes_to_messages.iteritems()
)

Then you can do lookups with []:

print error_codes_to_messages[2]
print error_messages_to_codes['foo']