Common exception types in Python - Step-by-Step Execution

Concept Flow - Common exception types

Start

↓

Run code

↓

Error occurs?

No→End

Yes↓

Identify exception type

↓

Handle or show error

↓

End

The program runs code, checks if an error happens, identifies the type of error, then handles or shows it before ending.

Execution Sample

Python

try:
    x = int('abc')
except ValueError as e:
    print('ValueError:', e)

This code tries to convert a string to an integer and catches a ValueError if it fails.

Execution Table

Step	Action	Evaluation	Result
1	Try to convert 'abc' to int	int('abc')	Raises ValueError
2	Catch ValueError exception	except ValueError as e	Exception caught
3	Print error message	print('ValueError:', e)	Output: ValueError: invalid literal for int() with base 10: 'abc'
4	End of try-except block	No more code	Program continues or ends

💡 Exception caught and handled, program does not crash

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	undefined	Exception raised, no value assigned	undefined	undefined
e	undefined	undefined	ValueError instance	ValueError instance

Key Moments - 3 Insights

Why does the program not crash when int('abc') fails?

Because the ValueError exception is caught in the except block (see execution_table step 2), so the error is handled gracefully.

What happens if the exception type in except does not match the error raised?

The exception is not caught and the program crashes. In the example, if except caught TypeError instead of ValueError, the ValueError would not be handled.

Can multiple exception types be caught in one except block?

Yes, by listing them in parentheses like except (TypeError, ValueError): to handle multiple error types together.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of variable 'x' after step 1?

A An integer value

B Undefined because exception was raised

C A string 'abc'

D None

💡 Hint

Check execution_table row 1 and variable_tracker for 'x' after step 1

At which step does the program print the error message?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at execution_table row 3 for the print action

If the except block was changed to except TypeError, what would happen?

A The ValueError would still be caught

B The program would print a TypeError message

C The program would crash with ValueError

D The program would ignore the error and continue silently

💡 Hint

Refer to key_moments about matching exception types

Concept Snapshot

Common exceptions in Python include ValueError, TypeError, ZeroDivisionError, and KeyError.
Use try-except blocks to catch and handle exceptions.
The except block must match the exception type to catch it.
Catching exceptions prevents program crashes and allows graceful error handling.

Full Transcript

This visual execution shows how Python handles common exceptions. The program tries to convert a string 'abc' to an integer, which raises a ValueError. The try-except block catches this error, preventing the program from crashing. The variable 'x' never gets a value because the exception stops the assignment. The exception object 'e' holds the error details and is printed. If the except block did not match the error type, the program would crash. This example teaches how to catch and handle common exceptions safely.