Lazy Crazy Coder's blog

Disassembler of Python byte code

Published at 20, March 2009, author art. Tags: optimization, python

Thanks to StackOverflow, I have discovered an interesting module in python's library — dis.

It is a disassembler of python byte code into mnemonics.

For example, for can view into a functions which create dicts:

>>> import dis
>>> def a():
...     return {'one': 1, 'two': 2}
...
>>> def b():
...     return dict(one=1, two=2)
...
>>> dis.dis(a)
  2           0 BUILD_MAP                0
              3 DUP_TOP
              4 LOAD_CONST               1 (1)
              7 ROT_TWO
              8 LOAD_CONST               2 ('one')
             11 STORE_SUBSCR
             12 DUP_TOP
             13 LOAD_CONST               3 (2)
             16 ROT_TWO
             17 LOAD_CONST               4 ('two')
             20 STORE_SUBSCR
             21 RETURN_VALUE
>>> dis.dis(b)
  2           0 LOAD_GLOBAL              0 (dict)
              3 LOAD_CONST               1 ('one')
              6 LOAD_CONST               2 (1)
              9 LOAD_CONST               3 ('two')
             12 LOAD_CONST               4 (2)
             15 CALL_FUNCTION          512
             18 RETURN_VALUE

Here, dis shows you, that dict is a function call, whereas {} is a pure python syntax construction. I think, that this module can be useful when you in doubt, why some constructions are more expensive than others.

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Disassembler of Python byte code — Lazy Crazy Coder's blog

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Comments

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24, March 2009, owner of http://pybites.blogspot.com/ said:

Yes, dis is an interesting module, but be wary of examining it too much from a performance standpoint. Python's opcodes can be very complicated individually, so the number of bytecode instructions is generally not a very good indicator of performance.

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