Python exception chaining

01_implicit_chaining.py

def implicit_chaining():
    """
    This is the Python 2 style. Just raising another exception from within an except block.
    In Python 3 this causes the exceptions to be chained with the message:
    
        During handling of the above exception, another exception occurred:
    
    Which is usually not correct when just re-raising with a more appropriate type.
    """
    try:
        1/0
    except Exception:
        raise RuntimeError('Something')

implicit_chaining()

01_implicit_chaining.pytb

Traceback (most recent call last):
  File "implicit_chaining.py", line 11, in implicit_chaining
    1/0
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "implicit_chaining.py", line 15, in <module>
    implicit_chaining()
  File "implicit_chaining.py", line 13, in implicit_chaining
    raise RuntimeError('Something')
RuntimeError: Something

02_explicit_chaining.py

def explicit_chaining():
    """
    This is the syntax to show that an exception has been caused by a previous one
    but it's not unexpected like in the previous example.
    The message used to chain the exception tracebacks in this case will be:

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

    This is useful when the original exception may contain information that can be helpful
    in debugging the issue etc.
    """
    try:
        1/0
    except Exception as ex:
        raise RuntimeError('Something') from ex

explicit_chaining()

02_explicit_chaining.pytb

Traceback (most recent call last):
  File "explicit_chaining.py", line 10, in explicit_chaining
    1/0
ZeroDivisionError: division by zero

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

Traceback (most recent call last):
  File "explicit_chaining.py", line 14, in <module>
    explicit_chaining()
  File "explicit_chaining.py", line 12, in explicit_chaining
    raise RuntimeError('Something') from ex
RuntimeError: Something

03_suppress_chaining.py

def suppress_chaining():
    """ 
    This will suppress any exceptions further down in the call stack and is 
    usually the preferred way in order to keep tracebacks short, unless 
    the 'parent' exceptions are useful to debugging as described above.
    """

    try:
        1/0
    except Exception:
        raise RuntimeError('Something') from None

suppress_chaining()

03_suppress_chaining.pytb

Traceback (most recent call last):
  File "suppress_chaining.py", line 13, in <module>
    suppress_chaining()
  File "suppress_chaining.py", line 11, in suppress_chaining
    raise RuntimeError('Something') from None
RuntimeError: Something