最好的做法是在Python if或if / elif语句的末尾包含else：pass语句吗？ [英] Is it best practice to include an else: pass statement at the end of a Python if or if/elif statement?

问题描述

如果我写：

if a == b:
    # do something
elif a == c:
    # do something else

我只是想通过其他方式，是在结尾写出以下要求？：

and I just want to pass otherwise, is writing out the following required at the end?:

else:
    pass

在没有解释器中的 else：语句的情况下似乎运行良好，是否存在我不知道我应该总是包括否则：在这些情况下传递？

It seems to run fine without the else: statement in the interpreter, is there a reason I'm not aware of that I should always include else: pass in these cases?

推荐答案

不，不是， else 套件完全是可选的。

No, it isn't, the else suite is entirely optional.

来自 if 声明文档：

From the if statement documentation:

if_stmt ::=  "if" expression ":" suite
             ( "elif" expression ":" suite )*
             ["else" ":" suite]

其中（...）* 表示零或更多和 [...] 表示可选。所以有效的 if 复合语句有一个如果行和套件，0或更多 elif 行和相应的套件，最多一个 else 行和套件，这是可选的。

where (...)* means zero or more, and [...] means optional. So a valid if compound statement has an if line and suite, 0 or more elif lines and corresponding suites, and at most one else line and suite, which is optional.

Python编译器将忽略任何 else：pass 块，包含它真的没有意义：

The Python compiler will ignore any else: pass block, there is really no point in including it:

>>> import dis
>>> dis.dis(compile('''\
... if True:
...     foo
... else:
...     pass
... ''', '<stdin>', 'exec'))
  1           0 LOAD_NAME                0 (True)
              3 POP_JUMP_IF_FALSE       13

  2           6 LOAD_NAME                1 (foo)
              9 POP_TOP             
             10 JUMP_FORWARD             0 (to 13)

  4     >>   13 LOAD_CONST               0 (None)
             16 RETURN_VALUE        
>>> dis.dis(compile('''\
... if True:
...     foo
... ''', '<stdin>', 'exec'))
  1           0 LOAD_NAME                0 (True)
              3 POP_JUMP_IF_FALSE       13

  2           6 LOAD_NAME                1 (foo)
              9 POP_TOP             
             10 JUMP_FORWARD             0 (to 13)
        >>   13 LOAD_CONST               0 (None)
             16 RETURN_VALUE        

其中唯一的区别是附加的行号到 LOAD_CONST 字节码，因为第一个源样本中有额外的行。

where the only difference is the line number attached to the LOAD_CONST bytecode because of the extra lines in the first source sample.

在风格上， else：传递只是混乱，是为了降低可读性。

Stylistically, else: pass is just clutter, something to reduce readability.

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