Python Errors and Built-in Exceptions

When Python (interpreter) encounters an error, it raises an exception. For example: division by zero. In this article, you will learn about the different built-in exception handling in Python.

When writing programs, we often encounter errors.

Errors caused by not following the correct structure (syntax) of the language are called syntax errors or parsing errors.

>>> if a <　3
　　File '<interactive input>', line　1
　　　　if a <　3
　　　　　　　　　　　^
SyntaxError: invalid syntax

Here we can notice that there is a colon missing in the if statement.

Errors may also occur at runtime, which are called exceptions. For example, when the file we try to open does not exist (FileNotFoundError), when we divide a number by zero (ZeroDivisionError), or when we cannot find the module we try to import (ImportError), such situations occur.

Each time this type of runtime error occurs, Python creates an exception object. If not handled properly, it will output the traceback of the error and some detailed information about the cause of the error.

>>>　1　/　0
Traceback (most recent call last):
　File '<string>', line　301, in runcode
　File '<interactive input>', line　1, in <module>
ZeroDivisionError: division by zero
>>> open('imaginary.txt')
Traceback (most recent call last):
　File '<string>', line　301, in runcode
　File '<interactive input>', line　1, in <module>
FileNotFoundError: [Errno　2] No such file or directory: 'imaginary.txt'

Built-in exceptions

Illegal operations may raise exceptions. There are many built-in exceptions in Python, which are raised when the corresponding errors occur. We can use the local() built-in function to view all built-in exceptions, as shown below.

>>> locals()['__builtins__']

This will return a dictionary of built-in exceptions, functions, and properties.

The following lists some common built-in exceptions in Python programming and the errors that cause them.

We can also define our own exceptions in Python (if needed). Visit this page to learn more aboutUser-defined exceptionsMore information.　

We can use try, except, and finally statementsHandle these built-in and user-defined exceptions in Python.