Python function hooks
I have been trying to find ways to wrap existing code to add hooks to Standard Python Library functions. One use-case is to track IO by counting the number of bytes that pass through os.read() and os.write().
I think that mock pattern is similar to this. I should look into the mock tools available for Python to see if they do the same thing as I am trying to do.
The following is a crude working version of the concept.
#!/usr/bin/env python # vim:set ft=python fileencoding=utf-8 sr et ts=4 sw=4 : See help 'modeline' import os import sys CHAR_COUNT_READ=0 CHAR_COUNT_WRITE=0 old_read = os.read old_write = os.write old_exit = sys.exit def read_hook(fd, n): global CHAR_COUNT_READ ss = old_read (fd, n) CHAR_COUNT_READ += len(ss) return ss def write_hook(fd, ss): global CHAR_COUNT_WRITE old_write (fd, ss) CHAR_COUNT_WRITE += len(ss) def exit_hook(code): global CHAR_COUNT_READ global CHAR_COUNT_WRITE print "exit hook script termination" print "os.read() processed %d characters" % CHAR_COUNT_READ print "os.write() processed %d characters" % CHAR_COUNT_WRITE old_exit(code) def write_hook_install(): global write_hook sys.write = write_hook def exit_hook_install(): global exit_hook sys.exit = exit_hook def read_hook_install(): global read_hook os.read = read_hook def script_runner(filename): _globals=globals() _globals['__name__']='__main__' execfile (filename, _globals) if __name__ == '__main__': try: if len(sys.argv) > 1: read_hook_install() write_hook_install() exit_hook_install() script_name = sys.argv sys.argv = sys.argv[1:] CHAR_COUNT_READ = 0 CHAR_COUNT_WRITE = 0 print "running ", script_name script_runner(script_name) print "normal script termination" print "os.read() processed %d characters" % CHAR_COUNT_READ print "os.write() processed %d characters" % CHAR_COUNT_WRITE else: print "Missing required argument of filename of Python script to run." print "The Python script to run should make use of os.read or os.write." except: print "os-wrap exception handler" print "os.read() processed %d characters" % CHAR_COUNT_READ print "os.write() processed %d characters" % CHAR_COUNT_WRITE