Python 3 – Exceptions Handling
In programming, exceptions are a common occurrence. They are unexpected occurrences that interrupt the normal flow of a program. Python has a built-in mechanism to handle such errors called exceptions handling.
In this article, we will discuss how to handle exceptions in Python 3. We will take a look at how to catch and handle exceptions, and also how to raise exceptions.
How to catch exceptions
When an exception is raised, Python stops the normal execution of the program and begins searching for a way to handle the exception. We can handle the exception using a try…except block.
try:
# code that raises the exception
except:
# code to handle the exception
The block that raises the exception goes inside the try block, while the code to handle the exception goes inside the except block.
Let’s take a look at an example:
try:
f = open('testfile.txt')
print(f.read())
f.close()
except:
print("An error occurred")
The above code will try to open a file named testfile.txt
, read its contents and close the file. If the file does not exist, an exception is raised and the control flows to the except block, which displays the message “An error occurred”.
In the above code, we’re catching all exceptions, but it’s best to catch specific exceptions so that we can handle them accordingly. We can specify the type of exception we want to catch using the except
statement.
try:
# code that raises the exception
except IOError:
# code to handle the IOError exception
except ValueError:
# code to handle the ValueError exception
except:
# code to handle any other exception
In the above code, if an IOError
exception is raised, the control flows to the IOError
block. If a ValueError
exception is raised, the control flows to the ValueError
block. If any other exception is raised, the control flows to the except
block at the end.
How to raise exceptions
Python allows us to raise exceptions ourselves when we encounter an error. We can raise an exception using the raise
statement.
raise Exception("An error occurred")
The above code raises an exception with the message “An error occurred”.
In some situations, we may need to raise a specific type of exception. Python comes with several built-in exception types, and we can also create our own custom exception types.
class MyCustomException(Exception):
pass
raise MyCustomException("My custom message")
The above code defines a custom exception type called MyCustomException
. We can raise this exception using the raise
statement with the message “My custom message”.
Conclusion
In summary, exception handling is a crucial part of programming. We don’t always know when an exception will occur, so it’s essential to have a mechanism in place to handle them when they do.
In Python, we handle exceptions using the try…except block. We can catch specific exceptions or catch all exceptions. We can also raise exceptions ourselves using the raise statement.
By using exception handling, we can create more robust and reliable programs. It helps us anticipate and handle errors gracefully, leading to more efficient coding and fewer bugs.