What is Try Except?

Try except handles errors gracefully in Python. Code in `try` block runs; if error occurs, `except` block catches it and program continues.

Basic Syntax

try:
    # Code that might cause error
    risky_operation()
except:
    # Handle the error
    print("An error occurred")

Simple Example

# Without try except - program crashes
number = int(input("Enter number: "))  # User enters "abc" → crash!

# With try except - handles error gracefully
try:
    number = int(input("Enter number: "))
    print(f"You entered: {number}")
except:
    print("That's not a valid number!")

Catching Specific Exceptions

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

try:
    number = int("abc")
except ValueError:
    print("Invalid number format!")

try:
    file = open("missing.txt")
except FileNotFoundError:
    print("File not found!")

Multiple Except Blocks

try:
    file = open("data.txt")
    number = int(file.read())
    result = 100 / number
except FileNotFoundError:
    print("File doesn't exist")
except ValueError:
    print("File doesn't contain a number")
except ZeroDivisionError:
    print("Number cannot be zero")
except Exception as e:
    print(f"Unexpected error: {e}")

Try Except Else Finally

try:
    file = open("data.txt")
    data = file.read()
except FileNotFoundError:
    print("File not found")
else:
    # Runs if NO exception occurred
    print(f"Successfully read: {data}")
finally:
    # ALWAYS runs (cleanup code)
    if 'file' in locals():
        file.close()
    print("Done")

Getting Error Details

try:
    result = 10 / 0
except Exception as e:
    print(f"Error type: {type(e).__name__}")
    print(f"Error message: {e}")
    print(f"Full details: {repr(e)}")

Common Exceptions

Exception	When It Occurs
ValueError	Invalid value type
TypeError	Wrong type operation
KeyError	Dictionary key missing
IndexError	List index out of range
FileNotFoundError	File doesn't exist
ZeroDivisionError	Division by zero
AttributeError	Invalid attribute

Best Practices

• Be specific: Catch specific exceptions, not generic Exception
• Don't hide errors: Log or report them
• Use finally: For cleanup (close files, connections)
• Don't use as control flow: Use for actual errors only
• Provide helpful messages: Tell users what went wrong

Real-World Examples

# File reading with error handling
try:
    with open("data.csv") as f:
        data = f.read()
except FileNotFoundError:
    print("Creating new file...")
    data = ""
except PermissionError:
    print("No permission to read file")

# API request with error handling
import requests
try:
    response = requests.get(url, timeout=5)
    response.raise_for_status()
    data = response.json()
except requests.Timeout:
    print("Request timed out")
except requests.HTTPError as e:
    print(f"HTTP error: {e}")
except requests.RequestException as e:
    print(f"Request failed: {e}")