Docs: error on page "1. Command line and environment"

[KingSupernova31]

Documentation

The page at https://docs.python.org/3/using/cmdline.html states, for the -O flag:

Remove assert statements and any code conditional on the value of debug.

But this is false, code conditional on the value of __debug__ is not removed.

[picnixz]

This is incorrect, see:

$ echo "if __debug__: print(1)" | python -O -m dis
  0           0 RESUME                   0

  1           2 LOAD_CONST               2 (None)
              4 RETURN_VALUE

versus (Py 3.11)

$ echo "if __debug__: print(1)" | python -m dis
  0           0 RESUME                   0

  1           2 PUSH_NULL
              4 LOAD_NAME                0 (print)
              6 LOAD_CONST               1 (1)
              8 PRECALL                  1
             12 CALL                     1
             22 POP_TOP
             24 LOAD_CONST               2 (None)
             26 RETURN_VALUE

[KingSupernova31]

@picnixz __debug__ is false when python is run with the -O flag, so that code is not testing what you seem to think it is. See here: https://docs.python.org/3/library/constants.html

[picnixz]

What I meant is: the code is eliminated. If you have a dynamic boolean, it will still emit code:

$ echo -e "z = False\nif z: print(1)" | python -m dis
  0           0 RESUME                   0

  1           2 LOAD_CONST               0 (False)
              4 STORE_NAME               0 (z)

  2           6 LOAD_NAME                0 (z)
              8 POP_JUMP_FORWARD_IF_FALSE    13 (to 36)
             10 PUSH_NULL
             12 LOAD_NAME                1 (print)
             14 LOAD_CONST               1 (1)
             16 PRECALL                  1
             20 CALL                     1
             30 POP_TOP
             32 LOAD_CONST               2 (None)
             34 RETURN_VALUE
        >>   36 LOAD_CONST               2 (None)
             38 RETURN_VALUE

So yes it is eliminating the dead code. It does not really matter in this case. What I meant it that there is no emitted bytecode. It's as if you have a #define macro. For assertions, we prune them at some point (I do not remember whether it is at the AST parse, compile or optimize phase though)

[picnixz]

As for how they are eliminated, whether it is because it is behind a "if False" block or not, is not important in the docs. What matters is that there will be no bytecode enitted for blocks guarded by __debug__.