[Python-ideas] Python docs page: In what ways is None special

[Michael Selik]

On Mon, Jul 23, 2018 at 2:03 AM Jonathan Fine <jfine2358 at gmail.com> wrote:

> Thank you for your attention. What have I missed?
>

None and a few other things are special-cased by CPython. The compiler
won't bother to write bytecode instructions when an if-statement obviously
evaluates false. That might surprise some folks.

    In [1]: import dis

    In [2]: def foo():
       ...:     if None:
       ...:         print(1)
       ...:     if 0:
       ...:         print(2)
       ...:     if 'a' == 'b':
       ...:         print(3)
       ...:

    In [3]: dis.dis(foo)
      6           0 LOAD_CONST               1 ('a')
                  2 LOAD_CONST               2 ('b')
                  4 COMPARE_OP               2 (==)
                  6 POP_JUMP_IF_FALSE       16

      7           8 LOAD_GLOBAL              0 (print)
                 10 LOAD_CONST               3 (3)
                 12 CALL_FUNCTION            1
                 14 POP_TOP
            >>   16 LOAD_CONST               0 (None)
                 18 RETURN_VALUE
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