Skip to main content

​
Basic try-except structure

The try block contains code that might fail. The except block runs if an error happens: 
try:
    # Code that might cause an error
    risky_operation()
except:
    # Code that runs if there's an error
    print("Something went wrong")

​
Catching specific errors

Different errors need different handling. Catch specific error types: 
try:
    age = int(input("Enter your age: "))
    print(f"In 10 years, you'll be {age + 10}")
except ValueError:
    print("Please enter a number")

​
Multiple error types

Handle different errors differently: 
try:
    # Read a number from a file
    with open('number.txt', 'r') as f:
        text = f.read()
    number = int(text)
    result = 100 / number
    print(f"Result: {result}")
except FileNotFoundError:
    print("Could not find number.txt")
except ValueError:
    print("File doesn't contain a valid number")
except ZeroDivisionError:
    print("Cannot divide by zero")

​
The else clause

Code in else runs only if no error happened: 
try:
    with open('data.txt', 'r') as f:
        data = f.read()
except FileNotFoundError:
    print("File not found")
else:
    # This only runs if the file was opened successfully
    print(f"File has {len(data)} characters")

​
The finally clause

Code in finally always runs, error or not: 
try:
    file = open('data.txt', 'r')
    data = file.read()
except FileNotFoundError:
    print("File not found")
finally:
    # This always runs to clean up
    if 'file' in locals() and not file.closed:
        file.close()
    print("Cleanup complete")
Don’t catch all errors with a bare except:. It hides problems and makes debugging harder. Always catch specific error types when possible.

​
Common mistakes

# Bad - catches everything
try:
    process_data()
except:
    pass  # Silent failure!

# Good - specific error
try:
    process_data()
except ValueError:
    print("Invalid data format")

# Bad - ignores the error
try:
    risky_operation()
except ValueError:
    pass

# Good - at least log it
try:
    risky_operation()
except ValueError:
    print("Warning: Invalid value encountered")

# Bad - hides all errors
try:
    critical_operation()
except Exception as e:
    print(f"Error: {e}")

# Good - log and re-raise
try:
    critical_operation()
except Exception as e:
    print(f"Critical error: {e}")
    raise  # Let the error propagate

​
What’s next?

Now let’s look at the most common errors you’ll encounter in Python.

Common errors

Errors you’ll see often