Book Image

The Python Apprentice

By : Robert Smallshire, Austin Bingham
Book Image

The Python Apprentice

By: Robert Smallshire, Austin Bingham

Overview of this book

Experienced programmers want to know how to enhance their craft and we want to help them start as apprentices with Python. We know that before mastering Python you need to learn the culture and the tools to become a productive member of any Python project. Our goal with this book is to give you a practical and thorough introduction to Python programming, providing you with the insight and technical craftsmanship you need to be a productive member of any Python project. Python is a big language, and it’s not our intention with this book to cover everything there is to know. We just want to make sure that you, as the developer, know the tools, basic idioms and of course the ins and outs of the language, the standard library and other modules to be able to jump into most projects.
Table of Contents (21 chapters)
Title Page
Credits
About the Authors
www.PacktPub.com
Customer Feedback
Preface
12
Afterword – Just the Beginning

Re-raising exceptions


Instead of returning an unPythonic error code, we can simply emit our error message and re-raise the exception object we're currently handling. This can be done by replacing the return -1 with a raise statement at the end of our exception handling block:

def convert(s):
    """Convert a string to an integer."""
    try:
        return int(s)
    except (ValueError, TypeError) as e:
        print("Conversion error: {}".format(str(e)), file=sys.stderr)
        raise

Without a parameter raise simply re-raises the exception that is currently being handled.

Testing in the REPL, we can see that the original exception type is re-raised whether it's a ValueError or a TypeError, and our Conversion error message is printed to stderr along the way:

>>> from exceptional import string_log
>>> string_log("25")
3.2188758248682006
>>> string_log("cat")
Conversion error: invalid literal for int() with base 10: 'cat'
Traceback (most recent call last):
  File "...