12.1 What are exceptions?

The first error that programmers (even experienced ones) are confronted with is when the code has incorrect syntax, meaning that the code instructions are not correctly formatted.

Consider this example of a syntax error:

>>> for i in range(10)
  File “<stdin>”, line 1
    for i in range(10)
                      ^
SyntaxError: invalid syntax

The error occurs because of a missing colon at the end of the for declaration. This is an example of an exception being raised. In the case of SyntaxError, it tells the programmer that the code has incorrect syntax and also prints the line where the error occurred, with an arrow pointing to where in that line the problem is.

Exceptions in Python are derived (inherited) from a base class called Exception. Python comes with a number of built-in exceptions. Some common exception types are listed in Table 12.1.

Here are two common examples of exceptions...