On Nov 24, 10:54 am, Steven D'Aprano <[EMAIL PROTECTED]
cybersource.com.au> wrote:
[snip]
>
> The correct solution to your example is to get rid of the attribute
> lookups from the expression completely:
"correct" in what sense?
>
> def abs(self):
> x, y, z = self.x, self.y, self.z
> return math.sqrt(x**2 + y**2 + z**2)
>
> It's probably also faster, because it looks up the attributes only once
> each, instead of twice.
Faster still is possible, without any cruft:
>>> def abs1(self):
... x, y, z = self.x, self.y, self.z
... return math.sqrt(x**2 + y**2 + z**2)
...
>>> def abs2(self):
... return math.sqrt(self.x**2 + self.y**2 + self.z**2)
...
>>> import dis
>>> dis.dis(abs1)
2 0 LOAD_FAST 0 (self)
3 LOAD_ATTR 0 (x)
6 LOAD_FAST 0 (self)
9 LOAD_ATTR 1 (y)
12 LOAD_FAST 0 (self)
15 LOAD_ATTR 2 (z)
18 ROT_THREE
19 ROT_TWO
20 STORE_FAST 1 (x)
23 STORE_FAST 2 (y)
26 STORE_FAST 3 (z)
3 29 LOAD_GLOBAL 3 (math)
32 LOAD_ATTR 4 (sqrt)
35 LOAD_FAST 1 (x)
38 LOAD_CONST 1 (2)
41 BINARY_POWER
42 LOAD_FAST 2 (y)
45 LOAD_CONST 1 (2)
48 BINARY_POWER
49 BINARY_ADD
50 LOAD_FAST 3 (z)
53 LOAD_CONST 1 (2)
56 BINARY_POWER
57 BINARY_ADD
58 CALL_FUNCTION 1
61 RETURN_VALUE
>>> dis.dis(abs2)
2 0 LOAD_GLOBAL 0 (math)
3 LOAD_ATTR 1 (sqrt)
6 LOAD_FAST 0 (self)
9 LOAD_ATTR 2 (x)
12 LOAD_CONST 1 (2)
15 BINARY_POWER
16 LOAD_FAST 0 (self)
19 LOAD_ATTR 3 (y)
22 LOAD_CONST 1 (2)
25 BINARY_POWER
26 BINARY_ADD
27 LOAD_FAST 0 (self)
30 LOAD_ATTR 4 (z)
33 LOAD_CONST 1 (2)
36 BINARY_POWER
37 BINARY_ADD
38 CALL_FUNCTION 1
41 RETURN_VALUE
>>>
HTH,
John
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