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__.

[KingSupernova31]

Eliminating dead code is not the same thing as eliminating code that is conditional on the value of __debug__.

echo "if not __debug__: print(1)" | python -O

[zware]

It's really not clear what you're arguing here. My best guess is that you're trying to say that the current docs suggest that both branches are eliminated, since both sides of the if __debug__ branch are "conditional on the value of __debug__"? If you have a concrete suggestion for improvement, that might go farther.