python - python列表和元组文字中的评估顺序

Question

假设我们有这样的事情:

a = (fcn1(), fcn2())
b = [fcn1(), fcn2()]

Python 解释器是在 fcn2() 之前评估 fcn1()，还是未定义顺序？

Answer 1

它们是从 left to right 评估的.

来自docs (对于列表):

When a comma-separated list of expressions is supplied, its elements are evaluated from left to right and placed into the list object in that order.

使用 dis.dis() 的小测试:

In [208]: def f1():pass

In [209]: def f2():pass

In [210]: import dis

In [212]: def func():

        a = (f1(), f2())
        b  = [f1(), f2()]
       .....:     

In [213]: dis.dis(func)
  2           0 LOAD_GLOBAL              0 (f1)
              3 CALL_FUNCTION            0
              6 LOAD_GLOBAL              1 (f2)
              9 CALL_FUNCTION            0
             12 BUILD_TUPLE              2
             15 STORE_FAST               0 (a)

  3          18 LOAD_GLOBAL              0 (f1)
             21 CALL_FUNCTION            0
             24 LOAD_GLOBAL              1 (f2)
             27 CALL_FUNCTION            0
             30 BUILD_LIST               2
             33 STORE_FAST               1 (b)
             36 LOAD_CONST               0 (None)
             39 RETURN_VALUE        

注意:在赋值的情况下，首先计算右侧。