How to programmatically set a global (module) variable?

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.

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

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)

Method 2

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

Method 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)

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0