In Python 2.7, you can do this by constructing a new code object and assigning it to a function’s func_code attribute. The function’s func_name is ignored by the traceback generation. Still, no eval necessary!

Running this:

from types import CodeType

def make_raiser(name, lineno, filename, type_to_raise):
    def raises():
        raise type_to_raise()
    co = raises.func_code
    raises.func_name = name
    raises.func_code = CodeType(
        co.co_argcount,
        co.co_nlocals,
        co.co_stacksize,
        co.co_flags,
        co.co_code,
        co.co_consts,
        co.co_names,
        co.co_varnames,
        filename,
        name,
        lineno - 1,
        co.co_lnotab,
        co.co_freevars,
        co.co_cellvars,
    )
    return raises

foo = make_raiser('foo', 3, 'foo.rs', lambda: IndexError(0))
bar = make_raiser('bar', 4, 'bar.rs', foo)
bar()

with python2.7 gives me this output:

$ python2 maketraceback.py 
Traceback (most recent call last):
  File "maketraceback.py", line 27, in <module>
    bar()
  File "bar.rs", line 4, in bar
  File "foo.rs", line 3, in foo
IndexError: 0

For Python3, there’s one extra argument to the CodeType constructor, so it’s just:

from types import CodeType

def make_raiser(name, lineno, filename, type_to_raise):
    def raises():
        raise type_to_raise()
    co = raises.__code__
    raises.__name__ = name
    raises.__code__ = CodeType(
        co.co_argcount,
        co.co_kwonlyargcount,
        co.co_nlocals,
        co.co_stacksize,
        co.co_flags,
        co.co_code,
        co.co_consts,
        co.co_names,
        co.co_varnames,
        filename,
        name,
        lineno - 1,
        co.co_lnotab,
        co.co_freevars,
        co.co_cellvars,
    )
    return raises

foo = make_raiser('foo', 3, 'foo.rs', lambda: IndexError(0))
bar = make_raiser('bar', 4, 'bar.rs', foo)
bar()

and output looks the same:

$ python3 maketraceback3.py 
Traceback (most recent call last):
  File "maketraceback3.py", line 29, in <module>
    bar()
  File "bar.rs", line 4, in bar
  File "foo.rs", line 3, in foo
IndexError: 0

Yes, this is what I’m planning for the next post :)