Python Exception Handling – Basic Examples
1. Basic try-except Block
python
# Basic exception handling
try:
num = int(input("Enter a number: "))
result = 10 / num
print(f"Result: {result}")
except:
print("Something went wrong!")
Example 1: Division with Zero Handling
python
# Handling division by zero error
try:
num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
result = num1 / num2
print(f"Result: {result}")
except ZeroDivisionError:
print("Error: Cannot divide by zero!")
Output:
text
Enter first number: 10 Enter second number: 0 Error: Cannot divide by zero!
Example 2: Invalid Input Handling
python
# Handling invalid input (non-integer values)
try:
age = int(input("Enter your age: "))
print(f"Your age is: {age}")
except ValueError:
print("Error: Please enter a valid number!")
Output:
text
Enter your age: twenty Error: Please enter a valid number!
Example 3: File Operations
python
# Handling file not found error
try:
with open("non_existent_file.txt", "r") as file:
content = file.read()
print(content)
except FileNotFoundError:
print("Error: File not found!")
Output:
text
Error: File not found!
Example 4: List Index Error
python
# Handling index out of range error
fruits = ["apple", "banana", "cherry"]
try:
index = int(input("Enter index (0-2): "))
print(f"Fruit at index {index}: {fruits[index]}")
except IndexError:
print("Error: Index out of range!")
except ValueError:
print("Error: Please enter a valid number!")
Output:
text
Enter index (0-2): 5 Error: Index out of range!
Example 5: Dictionary Key Error
python
# Handling key not found in dictionary
student = {"name": "John", "age": 20, "grade": "A"}
try:
key = input("Enter key to search (name/age/grade): ")
print(f"{key}: {student[key]}")
except KeyError:
print(f"Error: Key '{key}' not found in dictionary!")
Output:
text
Enter key to search (name/age/grade): city Error: Key 'city' not found in dictionary!
Bonus Example: Multiple Exception Handling
python
# Handling multiple types of exceptions
try:
num = int(input("Enter a number: "))
result = 100 / num
print(f"100 divided by {num} is {result}")
except ValueError:
print("Error: Please enter a valid integer!")
except ZeroDivisionError:
print("Error: Cannot divide by zero!")
except Exception as e:
print(f"Unexpected error: {e}")
Output:
text
Enter a number: abc Error: Please enter a valid integer!
Key Points:
- try block: Contains code that might raise exceptions
- except block: Catches and handles specific exceptions
- Specific exceptions: Better than catching all exceptions
- User-friendly messages: Help users understand what went wrong
- Prevention: Better than handling errors after they occur
These examples show how to gracefully handle common errors that might crash your program!
1. Basic try-except Block
python
# Basic exception handling
try:
num = int(input("Enter a number: "))
result = 10 / num
print(f"Result: {result}")
except:
print("Something went wrong!")
2. Handling Specific Exceptions
python
try:
num = int(input("Enter a number: "))
result = 10 / num
print(f"Result: {result}")
except ValueError:
print("Please enter a valid number!")
except ZeroDivisionError:
print("Cannot divide by zero!")
3. Handling Multiple Exceptions in One Block
python
try:
num = int(input("Enter a number: "))
result = 10 / num
print(f"Result: {result}")
except (ValueError, ZeroDivisionError):
print("Invalid input or division by zero!")
4. Using else Clause
python
try:
num = int(input("Enter a number: "))
result = 10 / num
except ValueError:
print("Please enter a valid number!")
except ZeroDivisionError:
print("Cannot divide by zero!")
else:
print(f"Success! Result: {result}") # Only runs if no exceptions
5. Using finally Clause
python
try:
num = int(input("Enter a number: "))
result = 10 / num
print(f"Result: {result}")
except ValueError:
print("Please enter a valid number!")
except ZeroDivisionError:
print("Cannot divide by zero!")
finally:
print("This always executes - cleanup code goes here")
6. Getting Exception Information
python
try:
num = int(input("Enter a number: "))
result = 10 / num
print(f"Result: {result}")
except Exception as e:
print(f"Error type: {type(e).__name__}")
print(f"Error message: {e}")
7. File Handling Example
python
try:
with open("myfile.txt", "r") as file:
content = file.read()
print(content)
except FileNotFoundError:
print("File not found!")
except PermissionError:
print("Permission denied!")
except IOError:
print("Error reading file!")
8. List Index Handling
python
my_list = [1, 2, 3, 4, 5]
try:
index = int(input("Enter index (0-4): "))
print(f"Value at index {index}: {my_list[index]}")
except ValueError:
print("Please enter a valid integer!")
except IndexError:
print("Index out of range!")
9. Dictionary Key Handling
python
student = {"name": "John", "age": 20, "grade": "A"}
try:
key = input("Enter key to search (name/age/grade/city): ")
print(f"{key}: {student[key]}")
except KeyError:
print(f"Key '{key}' not found in dictionary!")
10. Complete Example with All Clauses
python
def divide_numbers():
try:
num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
result = num1 / num2
except ValueError:
print("Please enter valid integers!")
return None
except ZeroDivisionError:
print("Cannot divide by zero!")
return None
except Exception as e:
print(f"Unexpected error: {e}")
return None
else:
print("Division successful!")
return result
finally:
print("Calculation completed!")
# Run the function
result = divide_numbers()
if result is not None:
print(f"Final result: {result}")
11. Nested Exception Handling
python
try:
# Outer try block
numbers = []
try:
# Inner try block
num = int(input("How many numbers? "))
for i in range(num):
value = int(input(f"Enter number {i+1}: "))
numbers.append(value)
except ValueError:
print("Invalid number entered!")
# Continue with outer block
if numbers:
average = sum(numbers) / len(numbers)
print(f"Average: {average}")
except ZeroDivisionError:
print("No numbers were entered!")
except Exception as e:
print(f"Unexpected error: {e}")
12. Simple Calculator with Error Handling
python
def calculator():
try:
num1 = float(input("Enter first number: "))
operator = input("Enter operator (+, -, *, /): ")
num2 = float(input("Enter second number: "))
if operator == '+':
result = num1 + num2
elif operator == '-':
result = num1 - num2
elif operator == '*':
result = num1 * num2
elif operator == '/':
result = num1 / num2
else:
print("Invalid operator!")
return
print(f"Result: {result}")
except ValueError:
print("Please enter valid numbers!")
except ZeroDivisionError:
print("Cannot divide by zero!")
except Exception as e:
print(f"An error occurred: {e}")
# Run calculator
calculator()
13. Input Validation with Retry
python
def get_valid_number():
while True:
try:
num = int(input("Enter a positive number: "))
if num <= 0:
raise ValueError("Number must be positive!")
return num
except ValueError as e:
print(f"Invalid input: {e}")
print("Please try again!")
# Usage
number = get_valid_number()
print(f"You entered: {number}")
Key Points to Remember:
- try: Code that might raise exceptions
- except: Handles specific exceptions
- else: Runs if no exceptions occur
- finally: Always runs (good for cleanup)
- Use specific exceptions instead of general
except: - Always handle exceptions gracefully for better user experience
These examples cover the fundamental concepts of exception handling in Python!
