Exceptions in Python

An exception is usually an event, that may not be an error that occurs during the code execution and stop the normal flow of that program. Python as a programming language raises an exception if the Python scripts met such a situation.

To make the script better, your code needs to keep working even when the unexpected happens. For example, let’s say your application needs to pull down information from the router, what happens if your application loses its connectivity?

Another common issue is what to do if the user enters invalid input or tries to open a file that is not present or deleted.

Exceptons Handling

Python comes with a special syntax that you can use to catch an exception. It is known as the try/except statement.

try:
  print(x)
except NameError:
  print("Vaiable 'x' is not defined")

Vaiable 'x' is not defined

Since the try block raises an error, the except block will be executed. Without the try block, the program will crash and raise an error.

Note

When you write the except without specifying the exception type, it is known as a bare exception, it is not recommended.

To catch multiple exceptions. Here is one way to do that:

x = '1'
y = 2

try:
  z = x + y
  print(z)
except:
  print("Something wrong")

Something wrong

finally Statement

There is more to the try/except statement than just try and except. You can add a finally statement to it as well. The finally statement is a block of code that will always get run even if there is an exception raised inside of the try portion. You can use the finally statement for cleanup.To do that, you can wrap the code in a try/except/finally statement.

try:
  1 / 0
except ZeroDivisionError:
  print('You can not divide by zero!')
finally:
  print('try/except block end.')

You can not divide by zero!
try/except block end.

Note

You can also skip the except statement entirely and create a try/finally

else Statement

There is one other statement that you can use with Python’s exception handling and that is the else statement. You can use the else statement to execute code when there are no exceptions.

try:
  print("Hello")
except:
  print("Something went wrong")
else:
  print("Nothing went wrong")

Hello
Nothing went wrong

See also

Full listing of the built-in exceptions, on Python documentation.