load python code at runtime

Question

I would like to load a .py file at runtime. This .py file is basically a config file with the following format:

var1=value  
var2=value  
predicate_function=func line : <return true or false>  

Once this file is loaded, I would like to be able to access var1, var2 and predicate_function. For each line, I'll pass it to the predicate function, and if it returns false, I'll ignore it.

In any case, I'm not sure how to load a python file at runtime and access its variables.

Clarification: there may be any number of these config files that I need to pass to the main program and I won't know their names until runtime. Google tells me I should use __import__. I'm not sure how to correctly use that method and then access the variables of the imported file.

Answer 1

As written in the python official documentation, if you just want to import a module by name, you can look it up in the sys.modules dictionary after using __import__.

Supposing your configuration is in myproject.mymodule, you would do like that :

module_name = 'myproject.mymodule'

import sys
__import__(module_name)
mymodule = sys.modules[module_name]

# Then you can just access your variables and functions
print mymodule.var1
print mymodule.var2
# etc...

You can also use the return value of __import__ statement but you will have to understand fully how python works with namespaces and scopes.

Answer 2

You just need to be able to dynamically specify the imports and then dynamically get at the variables.

Let's say your config file is bar.py and looks like this:

x = 3
y = 4
def f(x): return (x<4)

Then your code should look like this:

import sys

# somehow modnames should be a list of strings that are the names of config files
#
# you can do this more dynamically depending on what you're doing                                                                                                     
modnames = ['bar']

for modname in modnames:
  exec('import %s' % modname)

for modname in modnames:
  mod = sys.modules[modname]
  for k in mod.__dict__:
    if k[:2] != '__':
      print modname, k, mod.__dict__[k]

I get this output:

bar f <function f at 0x7f2354eb4cf8>
bar x 3
bar y 4

Then you at least have all the variables and functions. I didn't quite get what you wanted from the predicate functions, but maybe you can get that on your own now.