A pure Python C processor

dgelessus

From the guy with almost zero practical experience with C, here's a more-or-less functional C preprocessor, for all your C preprocessing needs: https://github.com/dgelessus/pythonista-c-utils/blob/master/preprocess.py

Features:

Macro constants and functions
- #define and #undef
- Macro constant and function substitution
- Stringification (#) and concatenation (##) in macro functions
- Macro functions internally use Python functions/callables, which means (relatively) easy wrapping of Python functions in macros
- Nested macro function calls work correctly
- Macro function arguments containing commas (such as array/struct literals) work correctly
Conditional blocks
- #ifdef, #ifndef, #else and #endif are fully functional
- #if and #elseif work in simple cases, more complex expressions require user input
File inclusion with #include
- Both angle-bracket and double-quote style are supported
- Argument may be a macro
#error and #warning cause Python exceptions and warnings respectively
#pragma and _Pragma always cause warnings
#line, __FILE__, __LINE__

Current issues and caveats:

Many constructs and features of the C preprocessor are supported, but that doesn't mean that you'll be able to process most standard header files. Those often rely on special environment-dependent macros provided by the preprocessor, such as __LP64__ indicating a 64-bit environment. By default only very few macros are provided.
The tokenizer is relatively dumb and knows little about C syntax, except for comments and string/char literals. This means that for example apostrophes (single quotes) in #error and the like cause problems if they aren't "balanced".
#if and #elif conditions have to be evaluated manually by the user, unless they are already a simple number literal.
The whole code isn't very pretty - although this is my third attempt or so, it is the first one that actually works well, which means the entire code isn't very polished yet.
Did I mention that I have almost no practical experience with C? It is entirely possible that I'm misunderstanding something about how C or the preprocessor works. If one of you folks who are more experienced in C find that I am wrong about something, please do tell me!