Earlier I wrote about Errors and Exceptions in Python. This post will be about how to handle those. Exception handling allows us to continue our program (or terminate it) if an exception occurs.
Error Handling
Error handling in Python is done through the use of exceptions that are caught in try blocks and handled in except blocks.
Try and Except
If an error is encountered, a try block code execution is stopped and transferred down to the except block.
In addition to using an except block after the try block, you can also use the final block.
The code in the finally block will be executed regardless of whether an exception occurs.
- Exception Handling in Python
- Exception Handling in Python: Writing a Robust Python Program
- How to Best Use Try-Except in Python
Raising an Exception
You can raise an exception in your own program by using the raise exception [, value] statement.
Raising an exception breaks current code execution and returns the exception back until it is handled.
Example
A try block look like below
try:
print "Hello World"
except:
print "This is an error message!"
Exception Errors
Some of the common exception errors are:
IOError – If the file cannot be opened.
ImportError – If python cannot find the module
ValueError – Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value
KeyboardInterrupt – Raised when the user hits the interrupt key (normally Control-C or Delete)
EOFError – Raised when one of the built-in functions (input() or raw_input()) hits an end-of-file condition (EOF) without reading any data
Example
Let’s have a look at some examples using exceptions.
except IOError:
print('An error occured trying to read the file.')
except ValueError:
print('Non-numeric data found in the file.')
except ImportError:
print "NO module found"
except EOFError:
print('Why did you do an EOF on me?')
except KeyboardInterrupt:
print('You cancelled the operation.')
except:
print('An error occured.')
There are a number of built-in exceptions in Python.