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In programming, errors are problems that occur during the execution or compilation of a program.

In Python, errors are divided mainly into syntax errors and exceptions.

If errors are not handled properly, they can cause your program to crash.

Types of Errors

1. Syntax Errors

• Occur when the Python parser detects incorrect syntax.
• Prevents the code from running.

For example,

# Missing colon
if True
    print("Hello")

Output

SyntaxError: expected ':'

2. Runtime Errors (Exceptions)

• Occur during the execution of a program.
• Can be handled using exception handling constructs.

For example,

# Division by zero
x = 10 / 0

Output

ZeroDivisionError: division by zero

Exception Handling

Python provides a mechanism to handle runtime errors using try-except.

Basic Syntax

try:
    # risky code
except SomeException:
    # handling code

For example,

try:
    number = int(input("Enter a number: "))
    print(10 / number)
except ZeroDivisionError:
    print("You can't divide by zero!")
except ValueError:
    print("Invalid input. Please enter a number.")

Common Built-in Exceptions

 Exception            Description                              
 -------------------  ---------------------------------------- 
 ZeroDivisionError    Raised when dividing by zero             
 ValueError           Invalid value passed to a function       
 TypeError            Invalid type operation                   
 IndexError           Accessing invalid index in a list        
 KeyError             Accessing a non-existent dictionary key  
 FileNotFoundError    File operation fails due to missing file 
 NameError            Using a variable that is not defined     

Using else and finally

• else runs if no exception occurs.
• finally always runs, even if there's an error.

For example,

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Error")
else:
    print("No errors occurred!")
finally:
    print("This always runs.")

Raising Exceptions Manually

We can raise your own exceptions using raise.

For example,

age = -5
if age < 0:
    raise ValueError("Age cannot be negative")

Custom Exceptions

Define our own exceptions by extending the Exception class.

For example,

class CustomError(Exception):
    pass

def check(value):
    if value > 100:
        raise CustomError("Value cannot exceed 100")

try:
    check(150)
except CustomError as e:
    print(f"Caught error: {e}")