[Tutor] introspection

[Alex Kleider]

On 2015-04-21 16:48, Cameron Simpson wrote:

> But it would not be schizophrenic to write a function that returned a
> name arbitrarily, by inspecting locals(). It depends whether you only
> need a name, or if you need "the" name.
> 
> Write yourself a "find_name_from_locals(local_map, value)" function
> that reports. That will (a) get you a partial answer and (b) cement in
> your mind what is possible and why. Easy and useful!
> 
> Cheers,
> Cameron Simpson <cs at zip.com.au>

Well I finally got around to tackling this little challenge and you are 
right:
It was illuminating.

For what it's worth, here's the code that made the light go on:
#!../venv/bin/python3
# -*- coding: utf-8 -*-
# vim: set file encoding=utf-8 :
#
# file: 'getname.py'
"""
Following through on:
Write yourself a "find_name_from_locals(local_map, value)" function that
reports. That will (a) get you a partial answer and (b) cement in your
mind what is possible and why. Easy and useful!
Cheers, Cameron Simpson <cs at zip.com.au>
"""
a = 'Alex'
j = 'June'
ssn = 681769931  # Totally ficticious!
# print(locals())
def get_name_1st_version(item):
     """What I naively thought would work."""
     for name in locals():
         if name == item:
             return name

def get_name(localmap, item):
     """As suggested.
     Returns 'a' name, not necessarily 'the' name."""
     for name in localmap:
         if localmap[name] == item:
             return name

if __name__ == '__main__':  # code block to run the application
     # First attempt:
     print(get_name_1st_version(a))
     print(get_name_1st_version(j))
     print(get_name_1st_version(ssn))
     print(get_name_1st_version('Alex'))
     print(get_name_1st_version('June'))
     print(get_name_1st_version(681769931))

     # Second attempt:
     localmap = locals()
     # Lesson learned: must use localmap created within the namespace
     # under scrutiny.
     print(get_name(localmap, a))
     print(get_name(localmap, j))
     print(get_name(localmap, ssn))
     print(get_name(localmap, 'Alex'))
     print(get_name(localmap, 'June'))
     print(get_name(localmap, 681769931))