How do I override a python import?
- by Evan Plaice
So I'm working on pypreprocessor which is a preprocessor that takes c-style directives and I've been able to make it work like a traditional preprocessor (it's self-consuming and executes postprocessed code on-the-fly) except that it breaks library imports.
The problem is. The preprocessor runs through the file, processes' it, outputs to a temp file, and exec() the temp file. Libraries that are imported need to be handled a little different because they aren't executed but rather loaded and made accessible to the caller module.
What I need to be able to do is. Interrupt the import (since the preprocessor is being run in the middle of the import), load the postprocessed code as a tempModule, and replace the original import with the tempModule to trick the calling script with the import into believing that the tempModule is the original module.
I have searched everywhere and so far, have no solution.
This question is the closest I've seen so far to providing an answer:
http://stackoverflow.com/questions/1096216/override-namespace-in-python
Here's what I have.
# remove the bytecode file created by the first import
os.remove(moduleName + '.pyc')
# remove the first import
del sys.modules[moduleName]
# import the postprocessed module
tmpModule = __import__(tmpModuleName)
# set first module's reference to point to the preprocessed module
sys.modules[moduleName] = tmpModule
moduleName is the name of the original module, tmpModuleName is the name of the postprocessed code file.
The strange part is, this solution still runs completely normal as if the first module completed loaded normally; unless you remove the last line, then you get a module not found error.
Hopefully someone on SO know a lot more about imports than I do because this one has me stumped.
