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GeezerVison is showing www.tutorialspoint.com — Python - Built-in Exceptions 
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Python - Built-in ExceptionsBuilt-in exceptions are pre-defined error classes in Python that handle errors and exceptional conditions in programs. They are derived from the base class "BaseException" and are part of the standard library. Standard Built-in Exceptions in PythonHere is a list of Standard Exceptions available in Python −
Here are some examples of standard exceptions − IndexErrorIt is shown when trying to access item at invalid index. numbers=[10,20,30,40] for n in range(5): print (numbers[n]) It will produce the following output − 10 20 30 40 Traceback (most recent call last): print (numbers[n]) IndexError: list index out of range ModuleNotFoundErrorThis is displayed when module could not be found. import notamodule Traceback (most recent call last): import notamodule ModuleNotFoundError: No module named 'notamodule' KeyErrorIt occurs as dictionary key is not found. D1={'1':"aa", '2':"bb", '3':"cc"}
print ( D1['4'])
Traceback (most recent call last):
D1['4']
KeyError: '4'
ImportErrorIt is shown when specified function is not available for import. from math import cube Traceback (most recent call last): from math import cube ImportError: cannot import name 'cube' StopIterationThis error appears when next() function is called after iterator stream exhausts. .it=iter([1,2,3]) next(it) next(it) next(it) next(it) Traceback (most recent call last): next(it) StopIteration TypeErrorThis is shown when operator or function is applied to an object of inappropriate type. print ('2'+2)
Traceback (most recent call last):
'2'+2
TypeError: must be str, not int
ValueErrorIt is displayed when function's argument is of inappropriate type. print (int('xyz'))
Traceback (most recent call last):
int('xyz')
ValueError: invalid literal for int() with base 10: 'xyz'
NameErrorThis is encountered when object could not be found. print (age) Traceback (most recent call last): age NameError: name 'age' is not defined ZeroDivisionErrorIt is shown when second operator in division is zero. x=100/0 Traceback (most recent call last): x=100/0 ZeroDivisionError: division by zero KeyboardInterruptWhen user hits the interrupt key normally Control-C during execution of program. name=input('enter your name')
enter your name^c
Traceback (most recent call last):
name=input('enter your name')
KeyboardInterrupt
Hierarchy of Built-in ExceptionsThe exceptions in Python are organized in a hierarchical structure, with "BaseException" at the top. Here is a simplified hierarchy −
How to Use Built-in ExceptionsAs we already know that built-in exceptions in Python are pre-defined classes that handle specific error conditions. Now, here is a detailed guide on how to use them effectively in your Python programs − Handling Exceptions with try-except BlocksThe primary way to handle exceptions in Python is using "try-except" blocks. This allows you to catch and respond to exceptions that may occur during the execution of your code. Example In the following example, the code that may raise an exception is placed inside the "try" block. The "except" block catches the specified exception "ZeroDivisionError" and handles it try:
result = 1 / 0
except ZeroDivisionError as e:
print(f"Caught an exception: {e}")
Following is the output obtained − Caught an exception: division by zero Handling Multiple ExceptionsYou can handle multiple exceptions by specifying them in a tuple within the "except" block as shown in the example below − try:
result = int('abc')
except (ValueError, TypeError) as e:
print(f"Caught a ValueError or TypeError: {e}")
Output of the above code is as shown below − Caught a ValueError or TypeError: invalid literal for int() with base 10: 'abc' Using "else" and "finally" BlocksThe "else" block is executed if the code block in the "try" clause does not raise an exception − try:
number = int(input("Enter a number: "))
except ValueError as e:
print(f"Invalid input: {e}")
else:
print(f"You entered: {number}")
Output of the above code varies as per the input given − Enter a number: bn Invalid input: invalid literal for int() with base 10: 'bn' The "finally" block is always executed, regardless of whether an exception occurred or not. It's typically used for clean-up actions, such as closing files or releasing resources − try:
file = open('example.txt', 'r')
content = file.read()
except FileNotFoundError as e:
print(f"File not found: {e}")
finally:
file.close()
print("File closed.")
Following is the output of the above code − File closed. Explicitly Raising Built-in ExceptionsIn Python, you can raise built-in exceptions to indicate errors or exceptional conditions in your code. This allows you to handle specific error scenarios and provide informative error messages to users or developers debugging your application. SyntaxFollowing is the basic syntax for raising built-in exception − raise ExceptionClassName("Error message")
ExampleIn this example, the "divide" function attempts to divide two numbers "a" and "b". If "b" is zero, it raises a "ZeroDivisionError" with a custom message − def divide(a, b):
if b == 0:
raise ZeroDivisionError("Cannot divide by zero")
return a / b
try:
result = divide(10, 0)
except ZeroDivisionError as e:
print(f"Error: {e}")
The output obtained is as shown below − Error: Cannot divide by zero 
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