对我来说，它们的速度几乎相同：（Debian上的Python 2.6.6）
In [4]: %timeit fact1(1)
10000000 loops, best of 3: 151 ns per loop
In [5]: %timeit fact2(1)
10000000 loops, best of 3: 154 ns per loop
字节码也非常相似：
In [6]: dis.dis(fact1)
2 0 LOAD_FAST 0 (n)
3 LOAD_CONST 1 (2)
6 COMPARE_OP 0 (<)
9 JUMP_IF_FALSE 5 (to 17)
12 POP_TOP
3 13 LOAD_CONST 2 (1)
16 RETURN_VALUE
>> 17 POP_TOP
5 18 LOAD_FAST 0 (n)
21 LOAD_GLOBAL 0 (fact)
24 LOAD_FAST 0 (n)
27 LOAD_CONST 2 (1)
30 BINARY_SUBTRACT
31 CALL_FUNCTION 1
34 BINARY_MULTIPLY
35 RETURN_VALUE
36 LOAD_CONST 0 (None)
39 RETURN_VALUE
In [7]: dis.dis(fact2)
2 0 LOAD_FAST 0 (n)
3 LOAD_CONST 1 (2)
6 COMPARE_OP 0 (<)
9 JUMP_IF_FALSE 5 (to 17)
12 POP_TOP
3 13 LOAD_CONST 2 (1)
16 RETURN_VALUE
>> 17 POP_TOP
4 18 LOAD_FAST 0 (n)
21 LOAD_GLOBAL 0 (fact)
24 LOAD_FAST 0 (n)
27 LOAD_CONST 2 (1)
30 BINARY_SUBTRACT
31 CALL_FUNCTION 1
34 BINARY_MULTIPLY
35 RETURN_VALUE
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