Using 'in' with a Dict

[Fredrik Lundh]

<cpmcdaniel at gmail.com> wrote:

>I was wondering if the following two "if" statements compile down to
> the same bytecode for a standard Dictionary type:
>
> m = {"foo": 1, "blah": 2}
>
> if "foo" in m:
>  print "sweet"
>
> if m.has_key("foo"):
>  print "dude"

nope.

>>> import dis
>>> dis.dis(compile("'foo' in dict", "", "exec"))
  1           0 LOAD_CONST               0 ('foo')
              3 LOAD_NAME                0 (dict)
              6 COMPARE_OP               6 (in)
              9 POP_TOP
             10 LOAD_CONST               1 (None)
             13 RETURN_VALUE
>>> dis.dis(compile("dict.has_key('foo')", "", "exec"))
  1           0 LOAD_NAME                0 (dict)
              3 LOAD_ATTR                1 (has_key)
              6 LOAD_CONST               0 ('foo')
              9 CALL_FUNCTION            1
             12 POP_TOP
             13 LOAD_CONST               1 (None)
             16 RETURN_VALUE

"in" is a built-in operator, "has_key" is an ordinary method.  both
paths end up in the same C function, but the method path is usually
a little bit slower.

</F>