I have just looked at the Python/import.c file and the hard coded PYC magic number... /* Magic word to reject .pyc files generated by other Python versions */ /* Change for each incompatible change */ /* The value of CR and LF is incorporated so if you ever read or write a .pyc file in text mode the magic number will be wrong; also, the Apple MPW compiler swaps their values, botching string constants */ /* XXX Perhaps the magic number should be frozen and a version field added to the .pyc file header? */ /* New way to come up with the magic number: (YEAR-1995), MONTH, DAY */ #define MAGIC (20121 | ((long)'\r'<<16) | ((long)'\n'<<24)) A bit outdated, I'd say. With the addition of Unicode, the PYC files will contain marshalled Unicode objects which are not readable by older versions. I'd suggest bumping the magic number to 50428 ;-) -- Marc-Andre Lemburg ______________________________________________________________________ Business: http://www.lemburg.com/ Python Pages: http://www.lemburg.com/python/