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Python: debug

lastmod 2021-10-08created 2021-10-083 edits

Optimization

The interpreter implements the __debug__ variable in an optimized way, so the extra if-statement control flow logic is not actually included in the code. You can check this with the dis package. 

from dis import dis


def main():
    print("run test.py", __debug__)

    if __debug__:
        print("debug run")
    else:
        print("release run")


main()

dis(main)

So if you run it as follows and look at the intermediate language of that main function depending on the -O option, 

c:\temp> python test.py
run test.py True
debug run
  6           0 LOAD_GLOBAL              0 (print)
              2 LOAD_CONST               1 ('run test.py')
              4 LOAD_CONST               2 (True)
              6 CALL_FUNCTION            2
              8 POP_TOP

  9          10 LOAD_GLOBAL              0 (print)
             12 LOAD_CONST               3 ('debug run')
             14 CALL_FUNCTION            1
             16 POP_TOP
             18 LOAD_CONST               0 (None)
             20 RETURN_VALUE

c:\temp> python -O test.py
run test.py False
release run
  6           0 LOAD_GLOBAL              0 (print)
              2 LOAD_CONST               1 ('run test.py')
              4 LOAD_CONST               2 (False)
              6 CALL_FUNCTION            2
              8 POP_TOP

 11          10 LOAD_GLOBAL              0 (print)
             12 LOAD_CONST               3 ('release run')
             14 CALL_FUNCTION            1
             16 POP_TOP
             18 LOAD_CONST               0 (None)
             20 RETURN_VALUE

As you can see, there is no COMPARE_OP at all from the if statement.

See also

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author Zer0 sitemap