Python Bidirectional Mapping

I'm not sure what to call what I'm looking for; so if I failed to find this question else where, I apologize. In short, I am writing python code that will interface directly with

Solution 1:

If you want to use two dicts, you can try this to create the inverted dict:

b = {v: k for k, v in a.iteritems()}

Solution 2:

Your solution leaves a lot of work do the repeated person creating the file. That is a source for error (you actually have to write each name three times). If you have a file where you need to update those from time to time (like, when new kernel releases come out), you are destined to include an error sooner or later. Actually, that was just a long way of saying, your solution violates DRY.

I would change your solution to something like this:

IFA_UNSPEC     =  0IFA_ADDRESS    =  1IFA_LOCAL      =  2IFA_LABEL      =  3IFA_BROADCAST  =  4IFA_ANYCAST    =  5IFA_CACHEINFO  =  6IFA_MULTICAST  =  7__IFA_MAX      =  8values = {globals()[x]:x for x in dir() if x.startswith('IFA_') or x.startswith('__IFA_')}

This was the values dict is generated automatically. You might want to (or have to) change the condition in the if statement there, according to whatever else is in that file. Maybe something like the following. That version would take away the need to list prefixes in the if statement, but it would fail if you had other stuff in the file.

values = {globals()[x]:x for x in dir() if not x.endswith('__')}

You could of course do something more sophisticated there, e.g. check for accidentally repeated values.

Solution 3:

What I ended up doing is leaving the constant values in the module and creating a dict. The module is ip_addr.py (the values are from linux/if_addr.h) so when constructing structs to send to the kernel I can use if_addr.IFA_LABEL and resolves responses with if_addr.values[2]. I'm hoping this is the most straight forward so when I have to look at this again in a year+ its easy to understand :p

IFA_UNSPEC     =  0
IFA_ADDRESS    =  1
IFA_LOCAL      =  2
IFA_LABEL      =  3
IFA_BROADCAST  =  4
IFA_ANYCAST    =  5
IFA_CACHEINFO  =  6
IFA_MULTICAST  =  7
__IFA_MAX      =  8

values = {
           IFA_UNSPEC    : 'IFA_UNSPEC',
           IFA_ADDRESS   : 'IFA_ADDRESS',
           IFA_LOCAL     : 'IFA_LOCAL',
           IFA_LABEL     : 'IFA_LABEL',
           IFA_BROADCAST : 'IFA_BROADCAST',
           IFA_ANYCAST   : 'IFA_ANYCAST',
           IFA_CACHEINFO : 'IFA_CACHEINFO',
           IFA_MULTICAST : 'IFA_MULTICAST',
           __IFA_MAX     : '__IFA_MAX'
         }