关于list范围问题

CODE:

from os.path import walk, join, normpath
import sys

if len(sys.argv) != 2:
    print 'argv error'
    sys.exit(0)

debug_str = 'PT(\"Press any and continue!\");\n'

def replace_c(file_c):
    f = file(file_c)
    all = f.readlines()
    f.close()

    for i in range(0, len(all)-1):
        if all[i] == debug_str :
            del all[i]

    ff = file(file_c, 'w')
    for i in range(0, len(all)-1):
        ff.write(all[i])
    ff.close()
   

def visit(arg, dirname, names):
    files=[normpath(join(dirname, file)) for file in names]

    for i in range(0, len(files)):
        if files[i][-2:] in ['.c'] :
            replace_c(files[i])
        if files[i][-4:] in ['.cpp'] :
            replace_c(files[i])
   
if __name__=="__main__":
    path=sys.argv[1]
    walk(path, visit, 0)