Variables in import statement python

Question

I'm trying to convert a script I had from bash to python. The way the program worked is that it had a Master script in the top folder and then in the subfolder Scripts a series of smaller, more specialised scripts. These smaller scripts might have names such as foo_bar.x, bar_foo.x, foo_baz.x, foo_qux.x, bar_qux.x, and so on. The Master script would collect the variables (as defined in files or from command line arguments) and execute the appropriate script with this sort of syntax:

VAR1=foo
VAR2=bar
./Scripts/${VAR1}_${VAR2}.x

This would execute Scripts/foo_bar.x

Now I'm trying to do the same but in python. The scripts are now modules in the folder Modules named foo_bar.py, foo_qux.py and so on. For now, the only thing they have is:

def test():
 print "This is foo_bar."

(or whichever).

If use these commands, this happens:

>>> import Modules.foo_bar
>>> Modules.foo_bar.test()
This is foo_bar.
>>> import Modules.foo_qux
>>> Modules.foo_qux.test()
This is foo_qux.
>>> a = Modules.foo_bar
>>> a.test()
This is foo_bar.

Which is fine. However, I can't get the syntax right if I want to use variables in the import statement. The first variable is defined as the string output of a command, and the second is a dictionary entry. Trying to use them in an import command gives an error.

>>> var1 = a_file.read_value()
>>> print var1
foo
>>> print dict['var2']
bar
>>> import Modules.var1_dict['var2']
 File "<stdin>", line 1
 import Modules.var1_dict['var2']
 ^
SyntaxError: invalid syntax

I assume it's a question of having the correct quotes or parentheses to properly invoke the variables. I've tried a bunch of combinations involving single quotes, curly brackets, square brackets, whatever, but no dice. What am I missing?

• Paul Rooney: Maybe see this.
• Łukasz Rogalski: Possible duplicate of Dynamic module import in Python

Answer 1

You can use the importlib library. And use like this:

...
import importlib
...
 function_call = 'Modules.' + var1 + dict['var2']
 function_call = importlib.import_module(function_call) 
 function_call.test()

• Pietro Aronica: This is close to working, but the importlib command should be
• user671150: @PietroAronica, Yeah the method is import_module, but you got the idea ))).
• Pietro Aronica: function_call = importlib.import_module(function_call)

Answer 2

If you want to import a module whose name is in a variable, you need to use __import__.

For example, let's create a dictionary whose values are the names of modules:

>>> d = { 1:'re', 2:'numpy' }

Now, let's import one of them:

>>> x = __import__(d[1])
>>> x
<module 're' from '/usr/lib/python2.7/re.pyc'>

We can use the module as long as we refer to it by the name we have given it:

>>> s='jerry'; x.sub('j', 'J', s)
'Jerry

And, to import the other:

>>> y = __import__(d[2])
>>> y
<module 'numpy' from '/home/jll/.local/lib/python2.7/site-packages/numpy/__init__.pyc'>
>>> y.array([1,3,2])
array([1, 3, 2])

Answer 3

How about executing your import statement dynamically?

Dummy example :

d = {"a" : "path"}
exec("import os.%s"%d["a"])
print os.path.abspath(__file__)