gistfile1.py

if __name__ == '__main__':
    import sys
    from jawa import JarFile, ConstantString

    try:
        from cStringIO import StringIO
    except ImportError:
        from StringIO import StringIO

    with JarFile(sys.argv[1]) as jf:
        for path in (p for p in jf.namelist if p.endswith('.class')):
            cf = ClassFile(StringIO(jf.read(path)))

            for c in cf.constants.find(ConstantString, lambda s: 'Minecraft 1.3.2' in s.string.value):
                with c.string as string:
                    string.value = string.value.replace('1.3.2', '1.5.0')

            o = StringIO()
            cf.save(o)
            jf.write(path, o.getvalue())
            o.close()

        jf.remove('META-INF/MOJANG_C.DSA')
        jf.remove('META-INF/MOJANG_C.SF')
        jf.save('minecraft.jar')