Raise an exception from a higher level, a la warnings

Question

In the module warnings (https://docs.python.org/3.5/library/warnings.html) there is the ability to raise a warning that appears to come from somewhere earlier in the stack:<

Answer 1

EDIT: The previous version did not provide quotes or explanations.

I suggest referring to PEP 3134 which states in the Motivation:

Sometimes it can be useful for an exception handler to intentionally re-raise an exception, either to provide extra information or to translate an exception to another type. The __cause__ attribute provides an explicit way to record the direct cause of an exception.

When an Exception is raised with a __cause__ attribute the traceback message takes the form of:

Traceback (most recent call last):
 

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  

To my understanding this is exactly what you are trying to accomplish; clearly indicate that the reason for the error is not your module but somewhere else. If you are instead trying to omit information to the traceback like your edit suggests then the rest of this answer won't do you any good.

---

Just a note on syntax:

The __cause__ attribute on exception objects is always initialized to None. It is set by a new form of the 'raise' statement:

   raise EXCEPTION from CAUSE

which is equivalent to:

    exc = EXCEPTION
    exc.__cause__ = CAUSE
    raise exc

so the bare minimum example would be something like this:

def function():
    int("fail")

def check_raise(function):
    try:
        function()
    except Exception as original_error:
        err = RuntimeError("An exception was raised.")
        raise err from original_error

check_raise(function)

which gives an error message like this:

Traceback (most recent call last):
  File "/PATH/test.py", line 7, in check_raise
    function()
  File "/PATH/test.py", line 3, in function
    int("fail")
ValueError: invalid literal for int() with base 10: 'fail'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/PATH/test.py", line 12, in 
    check_raise(function)
  File "/PATH/test.py", line 10, in check_raise
    raise err from original_error
RuntimeError: An exception was raised.

However the first line of the cause is the statement in the try block of check_raise:

  File "/PATH/test.py", line 7, in check_raise
    function()

so before raising err it may (or may not) be desirable to remove the outer most traceback frame from original_error:

except Exception as original_error:
    err = RuntimeError("An exception was raised.")
    original_error.__traceback__ = original_error.__traceback__.tb_next
    raise err from original_error

This way the only line in the traceback that appears to come from check_raise is the very last raise statement which cannot be omitted with pure python code although depending on how informative the message is you can make it very clear that your module was not the cause of the problem:

err = RuntimeError("""{0.__qualname__} encountered an error during call to {1.__module__}.{1.__name__}
the traceback for the error is shown above.""".format(function,check_raise))

---

The advantage to raising exception like this is that the original Traceback message is not lost when the new error is raised, which means that a very complex series of exceptions can be raised and python will still display all the relevant information correctly:

def check_raise(function):
    try:
        function()
    except Exception as original_error:
        err = RuntimeError("""{0.__qualname__} encountered an error during call to {1.__module__}.{1.__name__}
the traceback for the error is shown above.""".format(function,check_raise))
        original_error.__traceback__ = original_error.__traceback__.tb_next
        raise err from original_error

def test_chain():
    check_raise(test)

def test():
    raise ValueError

check_raise(test_chain)

gives me the following error message:

Traceback (most recent call last):
  File "/Users/Tadhg/Documents/test.py", line 16, in test
    raise ValueError
ValueError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/Tadhg/Documents/test.py", line 13, in test_chain
    check_raise(test)
  File "/Users/Tadhg/Documents/test.py", line 10, in check_raise
    raise err from original_error
RuntimeError: test encountered an error during call to __main__.check_raise
the traceback for the error is shown above.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/Tadhg/Documents/test.py", line 18, in 
    check_raise(test_chain)
  File "/Users/Tadhg/Documents/test.py", line 10, in check_raise
    raise err from original_error
RuntimeError: test_chain encountered an error during call to __main__.check_raise
the traceback for the error is shown above.

Yes it is long but it is significantly more informative then:

Traceback (most recent call last):
  File "/Users/Tadhg/Documents/test.py", line 18, in 
    check_raise(test_chain)
RuntimeError: An exception was raised.

not to mention that the original error is still usable even if the program doesn't end:

import traceback

def check_raise(function):
    ...

def fail():
    raise ValueError

try:
    check_raise(fail)
except RuntimeError as e:
    cause = e.__cause__
    print("check_raise failed because of this error:")
    traceback.print_exception(type(cause), cause, cause.__traceback__)

print("and the program continues...")