.. getthecode:: exceptions.py
    :language: python3
    :hidden:

============
 Exceptions
============

This page contains a memo on exceptions.

For a complete reference documentation, look at https://docs.python.org/3/reference/compound_stmts.html#try


.. code-block:: py3

    from Tools import *
    

Catch exceptions using :code:`try` block:


.. code-block:: py3

    try:
        x = 1 / 0
    except ZeroDivisionError as exception:
        pretty_print((exception, exception.__traceback__))
    except ZeroDivisionError:
        # If we don't need the exception instance
        print('try block failed')
    except Exception as exception:
        # Catch all exceptions
        print(exception)
    except:
        # Shorter form to catch all exceptions
        pass # simply ignore the exception

.. code-block:: none

        (   ZeroDivisionError('division by zero',),
            <traceback object at 0x7f090cc5cf08>)
    

Use :code:`finally` to do cleanup:


.. code-block:: py3

    try:
        x = 1 / 1
    except Exception as exception:
        print(exception)
    finally:
        print('try block succeed')

.. code-block:: none

    try block succeed
    

Raise exceptions:


.. code-block:: py3

    try:
        raise NameError("Something bad happened")
    except Exception as exception:
        print(exception)

.. code-block:: none

    Something bad happened
    

.. code-block:: py3

    try:
        try:
            1 / 0
        except ZeroDivisionError:
            raise # last exception
    except Exception as exception:
        print(exception)

.. code-block:: none

    division by zero
    

Chain exceptions:


.. code-block:: py3

    try:
        try:
            1 / 0
        except ZeroDivisionError as exception:
            raise NameError("Something bad happened") from exception
    except Exception as exception:
        print(exception, ', caused by:', exception.__cause__)

.. code-block:: none

    Something bad happened , caused by: division by zero
    
**To be completed:** :code:`exception.__context__`