import struct

__all__ = ['magics', 'versions']

def __build_magic(magic):
    return struct.pack('Hcc', magic, '\r', '\n')

def __by_version(magics):
    by_version = {}
    for m, v in magics.items():
        by_version[v] = m
    return by_version

versions = {
    # taken from from Python/import.c
    # magic, version
    __build_magic(20121): '1.5', #1.5, 1.5.1, 1.5.2
    __build_magic(50428): '1.6', #1.6
    __build_magic(50823): '2.0', #2.0, 2.0.1
    __build_magic(60202): '2.1', #2.1, 2.1.1, 2.1.2
    __build_magic(60717): '2.2', #2.2
    __build_magic(62011): '2.3', #2.3a0
    __build_magic(62021): '2.3', #2.3a0
    __build_magic(62041): '2.4', #2.4a0
    __build_magic(62051): '2.4', #2.4a3
    __build_magic(62061): '2.4', #2.4b1
    __build_magic(62071): '2.5', #2.5a0
    __build_magic(62081): '2.5', #2.5a0 (ast-branch)
    __build_magic(62091): '2.5', #2.5a0 (with)
    __build_magic(62092): '2.5', #2.5a0 (changed WITH_CLEANUP opcode)
    __build_magic(62101): '2.5', #2.5b3 (fix wrong code: for x, in ...)
    __build_magic(62111): '2.5', #2.5b3 (fix wrong code: x += yield)
    __build_magic(62121): '2.5', #2.5c1 (fix wrong lnotab with for loops and
                           # storing constants that should have been removed
    __build_magic(62131): '2.5', #2.5c2 (fix wrong code: for x, in ... in listcomp/genexp)
    __build_magic(62151): '2.6', #2.6a0 (peephole optimizations & STORE_MAP)
    __build_magic(62161): '2.6', #2.6a1 (WITH_CLEANUP optimization)
    __build_magic(62171): '2.7', #2.7a0 (optimize list comprehensions/change LIST_APPEND)
    __build_magic(62181): '2.7', #2.7a0 (optimize conditional branches:
    # introduce POP_JUMP_IF_FALSE and POP_JUMP_IF_TRUE)
    __build_magic(62191): '2.7', #2.7a0 (introduce SETUP_WITH)
    __build_magic(62201): '2.7', #2.7a0 (introduce BUILD_SET)
    __build_magic(62211): '2.7', #2.7a0 (introduce MAP_ADD and SET_ADD)
    __build_magic(3000): '3.0',  #3.000 
    __build_magic(3010): '3.0',  #3.000 (removed UNARY_CONVERT)
    __build_magic(3020): '3.0',  #3.000 (added BUILD_SET)
    __build_magic(3030): '3.0',  #3.000 (added keyword-only parameters)
    __build_magic(3040): '3.0',  #3.000 (added signature annotations)
    __build_magic(3050): '3.0',  #3.000 (print becomes a function)
    __build_magic(3060): '3.0',  #3.000 (PEP 3115 metaclass syntax)
    __build_magic(3061): '3.0',  #3.000 (string literals become unicode)
    __build_magic(3071): '3.0',  #3.000 (PEP 3109 raise changes)
    __build_magic(3081): '3.0',  #3.000 (PEP 3137 make __file__ and __name__ unicode)
    __build_magic(3091): '3.0',  #3.000 (kill str8 interning)
    __build_magic(3101): '3.0',  #3.000 (merge from 2.6a0, see 62151)
    __build_magic(3103): '3.0',  #3.000 (__file__ points to source file)
    __build_magic(3111): '3.0',  #3.0a4 (WITH_CLEANUP optimization).
    __build_magic(3131): '3.0',  #3.0a5 (lexical exception stacking, including POP_EXCEPT)
    __build_magic(3141): '3.1',  #3.1a0 (optimize list, set and dict comprehensions)
    __build_magic(3151): '3.1',  #3.1a0 (optimize conditional branches)
    __build_magic(3160): '3.2',  #3.2a0 (add SETUP_WITH)
    __build_magic(3170): '3.2',  #3.2a1 (add DUP_TOP_TWO, remove DUP_TOPX and ROT_FOUR)
    __build_magic(3180): '3.2',  #3.2a2 (add DELETE_DEREF)
}

magics = __by_version(versions)

def __show(text, magic):
    print text, struct.unpack('BBBB', magic), \
          struct.unpack('HBB', magic)

def test():
    import imp
    magic_20 = by_version['2.0']
    current = imp.get_magic()
    current_version = magics[current]
    magic_current = by_version[ current_version ]
    print type(magic_20), len(magic_20), repr(magic_20)
    print
    print 'This Python interpreter has version', current_version
    __show('imp.get_magic():\t', current),
    __show('magic[current_version]:\t', magic_current)
    __show('magic_20:\t\t', magic_20)
    
if __name__ == '__main__':
    test()