python-2.7 - Python 2 dis.dis() 无法解析包含 `for` 循环语法的字符串

Question

使用 Python 3，dis.dis()适用于解析包含 for 循环语法的字符串:

>>> import dis
>>> dis.dis('for _ in range(10): pass')
  1           0 SETUP_LOOP              20 (to 23)
              3 LOAD_NAME                0 (range)
              6 LOAD_CONST               0 (10)
              9 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
             12 GET_ITER
        >>   13 FOR_ITER                 6 (to 22)
             16 STORE_NAME               1 (_)
             19 JUMP_ABSOLUTE           13
        >>   22 POP_BLOCK
        >>   23 LOAD_CONST               1 (None)
             26 RETURN_VALUE

在 Python 2 中，它产生了 string index out of range 错误:

In [30]: dis.dis('for _ in range(10): pass')
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-30-b7c7c1c77064> in <module>()
----> 1 dis.dis('for _ in range(10): pass')

/usr/lib/python2.7/dis.pyc in dis(x)
     43         disassemble(x)
     44     elif isinstance(x, str):
---> 45         disassemble_string(x)
     46     else:
     47         raise TypeError, \

/usr/lib/python2.7/dis.pyc in disassemble_string(code, lasti, varnames, names, constants)
    110 def disassemble_string(code, lasti=-1, varnames=None, names=None,
    111                        constants=None):
--> 112     labels = findlabels(code)
    113     n = len(code)
    114     i = 0

/usr/lib/python2.7/dis.pyc in findlabels(code)
    164         i = i+1
    165         if op >= HAVE_ARGUMENT:
--> 166             oparg = ord(code[i]) + ord(code[i+1])*256
    167             i = i+2
    168             label = -1

IndexError: string index out of range

甚至将 for 循环包装在函数中以实现常规语法也无济于事:

def test():
    for _ in range(10):
        pass

dis.dis('test')
<The same error>

这是错误还是其他地方记录的期望行为？

软件版本

$ python2 -V
Python 2.7.9

$ python3 -V
Python 3.4.2

$ cat /etc/os-release 
PRETTY_NAME="Debian GNU/Linux 8 (jessie)"
NAME="Debian GNU/Linux"
VERSION_ID="8"
VERSION="8 (jessie)"
ID=debian
HOME_URL="http://www.debian.org/"
SUPPORT_URL="http://www.debian.org/support/"
BUG_REPORT_URL="https://bugs.debian.org/"

Answer 1

Python 2 的 dis.dis 不接受包含 Python 代码的字符串作为参数，它接受包含字节码 或函数的字符串。

你最好的选择是这样的:

>>> def test():
...     for _ in range(10):
...         pass
...
>>>
>>> import dis
>>> dis.dis(test)
  2           0 SETUP_LOOP              20 (to 23)
              3 LOAD_GLOBAL              0 (range)
              6 LOAD_CONST               1 (10)
              9 CALL_FUNCTION            1
             12 GET_ITER
        >>   13 FOR_ITER                 6 (to 22)
             16 STORE_FAST               0 (_)

  3          19 JUMP_ABSOLUTE           13
        >>   22 POP_BLOCK
        >>   23 LOAD_CONST               0 (None)
             26 RETURN_VALUE