How to use Python's Try and Except

try blocks allow you to test blocks of code to find errors.

except block allows you to handle errors.

finally blocks allow you to execute code regardless of the results of try and except blocks.

Exception handling

When we call Python and an error or exception occurs, it usually stops and generates an error message.

These exceptions can be handled using a try statement:

Example

The try block will generate an exception because x is undefined:

try:
  print(x)
except:
  print("An exception occurred")

Run Example

#Since the try block throws an error, the except block will be executed.

Without the try block, the program will crash and throw an error:

Example

This statement will throw an error because x is not defined:

print(x)

Multiple exceptions

You can define as many exception blocks as you need, for example, if you want to execute a special code block for a special type of error:

Example

Print a message if the try block raises NameError, and another message if it is another error:

try:
  print(x)
except NameError:
  print("Variable x is not defined")
except:
  print("Something else went wrong")

Run the instance

Else

If no error is raised, then you can use the else keyword to define a block of code to be executed:

Example

In this case, the try block will not generate any errors:

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

Run the instance

Finally

If the finally block is specified, Then the finally block will be executed regardless of whether the try block raises an error.

Instance

try:
  print(x)
except:
  print("Something went wrong")
finally:
  print("The 'try except' is finished")

Running Instance

##This is useful for closing objects and cleaning up resources

Example

Attempt to open and write to a non-writable file:

try:
  f = open("demofile.txt")
  f.write("Lorum Ipsum")
except:
  print("Something went wrong when writing to the file")
finally:
  f.close()

Run Example

Program You can continue without opening the file object.

Throwing exceptions

As a Python developer, you can choose to throw exceptions when conditions occur.

To throw (raise) an exception, please use the raise keyword.

Example

If x is less than 0, an exception is thrown and the program is terminated:

x = -1
if x < 0:
  raise Exception("Sorry, no numbers below zero")

Running example

raise keyword is used to raise exceptions.

You can define the type of exception raised and the text printed to the user.

Example

If x is not an integer, TypeError is raised:

x = "hello"
if not type(x) is int:
  raise TypeError("Only integers are allowed")

Running Example

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