How to programmatically set a global (module) variable?

Question

I would like to define globals in a "programmatic" way. Something similar to what I want to do would be:

definitions = {'a': 1, 'b': 2, 'c': 123.4}
for definition in definitions.items():
    exec("%s = %r" % definition)  # a = 1, etc.

Specifically, I want to create a module fundamentalconstants that contains variables that can be accessed as fundamentalconstants.electron_mass, etc., where all values are obtained through parsing a file (hence the need to do the assignments in a "programmatic" way).

Now, the exec solution above would work. But I am a little bit uneasy with it, because I'm afraid that exec is not the cleanest way to achieve the goal of setting module globals.

Answer 1

You can set globals in the dictionary returned by globals():

definitions = {'a': 1, 'b': 2, 'c': 123.4}
for name, value in definitions.items():
    globals()[name] = value

Answer 2

Here is a better way to do it:

import sys
definitions = {'a': 1, 'b': 2, 'c': 123.4}
module = sys.modules[__name__]
for name, value in definitions.iteritems():
    setattr(module, name, value)

Answer 3

You're right, exec is usually a bad idea and it certainly isn't needed in this case.

Ned's answer is fine. Another possible way to do it if you're a module is to import yourself:

fundamentalconstants.py:

import fundamentalconstants

fundamentalconstants.life_meaning= 42

for line in open('constants.dat'):
    name, _, value= line.partition(':')
    setattr(fundamentalconstants, name, value)