在运行动态编译的代码对象时，如何在回溯中保留源代码行？

Question

Say I use compile to create a code object from a string and a name:

>>> a = compile('raise ValueError\n', '<at runtime>', 'exec')

I would like the lines within that string to appear within the traceback (note - the following is run in IDLE):

>>> exec(a)
Traceback (most recent call last):
 File "<pyshell#11>", line 1, in <module>
    exec(c)
  File "<at runtime>", line 1, in <module>
    raise ValueError   <-- This line is what I want
ValueError

Alas, they do not:

>>> exec(a)
Traceback (most recent call last):
 File "<pyshell#11>", line 1, in <module>
    exec(c)
  File "<at runtime>", line 1, in <module>
ValueError

Without creating a temporary file, how do I make that raise ValueError line appear in the traceback?

Answer 1

Using the undocumented cache member of the builtin linecache , this seems to work:

def better_compile(src, name, mode):
    # there is an example of this being set at
    # https://hg.python.org/cpython/file/2.7/Lib/linecache.py#l104
    from linecache import cache
    cache[name] = (
        len(src), None,
        [line+'\n' for line in src.splitlines()], name
    )
    return compile(src, name, mode)

>>> c = better_compile('raise ValueError\n', '<a name>', 'exec')
>>> exec(c)
Traceback (most recent call last):
  File "<pyshell#50>", line 1, in <module>
    exec(c)
  File "<a name>", line 1, in <module>
    raise ValueError
ValueError

---

It turns out this is pretty much how IDLE does it

Answer 2

Well, you could write your own exception handler which fills the data:

code = """
def f1():
    f2()

def f2():
    1 / 0

f1()
"""

a = compile(code, '<at runtime>', 'exec')

import sys
import traceback

try:
    exec(a)
except:
    etype, exc, tb = sys.exc_info()
    exttb = traceback.extract_tb(tb)

    ## Fill the missing data:
    exttb2 = [(fn, lnnr, funcname,
               (code.splitlines()[lnnr-1] if fn=='<at runtime>'
                else line))
              for fn, lnnr, funcname, line in exttb]

    # Print:
    sys.stderr.write('Traceback (most recent call last):\n')
    for line in traceback.format_list(exttb2):
        sys.stderr.write(line)
    for line in traceback.format_exception_only(etype, exc):
        sys.stderr.write(line)

Result:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "<at runtime>", line 8, in <module>
    f1()
  File "<at runtime>", line 3, in f1
    f2()
  File "<at runtime>", line 6, in f2
    1 / 0
ZeroDivisionError: integer division or modulo by zero

Now just wrap that compile & exec into a smart_exec function to call every time...