Python-module: #ifdef for setup.py

Question

I am building a python module and I am somehow stuck. I would like to make some features optional, i.e. so that they are simply not there if disabled (even not the methods).

My module consists of C and Python parts; and I search something similar to #ifdefs for the Python, because if one feature in C is disabled then the Python related stuff should NOT be installed.

Any suggestions?

Answer 1

There's no such thing, at least, not as it works in C.

Instead, I'd recommend you to something like this:

• If a part is made optional as it requires more 3rd party libraries to be installed, define some extras in setup.py See here

• If you want to support "pluggable" features (eg. some kind of plugin, ...) use setuptools' entry points and split features across multiple packages. Then, install only the packages you need.

Answer 2

It's not that different from any other kind of if statement. The thing is, function definitions (not just declarations) are actually just like any other code, so you can do something like this (copy to a separate file and import as module):

X = 1

class A(object):
    def __init__(self):
        pass

    def funcA(self):
        return 'A'

    if X == 0:
        def funcB(self):
            return 'B'

 # then at console, if above is called 'modtest.py'...
 import modtest
 a = modtest.A()
 a.<tab>
 a.funcA

 # Now change the above to say X = 0, and
 reload(modtest)
 a2 = modtest.A()
 a2.<tab>
 a2.funcA a2.funcB

The if X == 0 actually determines whether python will run the code that defines the function. Note that this is done at module import time - you can't change X 'on the fly' and get some A classes with funcB and some without; it only checks X once, when defining the class, and from then on just passes back the class A it already parsed.