Mimic C preprocessor with Python/Ruby?

Question

I need to mimic the preprocessor feature of C with Python.

If I want to run the debug release, I use as follows with C

#ifdef DEBUG
printf(...)
#endif

I just use -DDEBUG or similar to trigger it on or off.

What method can I use for Python/Ruby? I mean, what should I do to control the behavior of python/ruby scripts in such a way that I can change a variable that affects all the script files in a project?

Answer 1

You usually use the python logging functionality in this use-case. That is configured in configuration files, and you can set the output levels. Very close in usage to java log4j, if you're familiar with that.

Answer 2

You can almost use the actual C preprocessor. If you rename your file to end in .c, you can then do this: gcc -w -E input/file.py.c -o output/file.py.

The main issue seems to be with comments. The preprocessor will complains about python comment lines being invalid preprocessor directives. You can remedy this by using C++ comments (// comment).

Or, a better idea would be to just write your own simple preprocessor. If you only need #define functionality, you're just talking about a doing a search and replace on your file.

Another solution would be something like this:

def nothing(*args):
    pass

def print_debug(msg):
    print msg

if not DEBUG: 
    print_debug = nothing

That way your print statements don't do anything if you're not in debug mode.

Answer 3

I wrote pypreprocessor to do exactly what you described.

Not only can it preprocess source files and handle #define and #ifdef but it also includes some features that make it more than just an on-the-fly preprocessor.

If you're worried about the added performance hit of using a preprocessor, you can set a few optional variables and make the preprocessor output to a clean source file with all of the metadata removed.

Check out the project on Google Code for more info.

The latest release can also be accessed through the PYPI