Handling specific exceptions in Python - Step-by-Step Execution

Concept Flow - Handling specific exceptions

Start try block

↓

Execute code

↓

Exception occurs?

No→End try block

Yes↓

Match exception type?

No→Unhandled exception

Yes↓

Run except block

↓

Continue after try-except

The program tries to run code. If an error happens, it checks if the error matches a specific type. If yes, it runs the matching except block. Otherwise, the error is not handled here.

Execution Sample

Python

try:
    x = int('abc')
except ValueError:
    print('ValueError caught')

This code tries to convert a string to an integer. If it fails with a ValueError, it prints a message.

Execution Table

Step	Action	Evaluation	Result
1	Enter try block	int('abc')	Raises ValueError
2	Exception occurs?	ValueError raised	Yes
3	Match exception type?	Is exception ValueError?	Yes
4	Run except block	print('ValueError caught')	Output: ValueError caught
5	Continue after try-except	No more code	Program ends normally

💡 Exception ValueError caught and handled, program continues normally

Variable Tracker

Variable	Start	After Step 1	After Step 4	Final
x	undefined	exception raised, no assignment	undefined	undefined

Key Moments - 3 Insights

Why is variable x never assigned a value?

Because int('abc') raises a ValueError before x can be assigned, as shown in execution_table step 1.

What happens if the exception type does not match the except block?

The exception is not handled here and will cause the program to stop or look for another handler, as explained in concept_flow step 'Match exception type?--No'.

Why does the program continue after the except block?

Because the exception was caught and handled, so the program moves on normally, as seen in execution_table step 5.

Visual Quiz - 3 Questions

Look at the execution table, what happens at step 3?

A The program ends

B The program checks if the exception is a ValueError

C The program assigns a value to x

D The program prints the exception message

💡 Hint

See execution_table row 3 where it checks exception type

At which step does the program print 'ValueError caught'?

A Step 4

B Step 1

C Step 2

D Step 5

💡 Hint

Look at execution_table row 4 for the print action

If the except block was for KeyError instead of ValueError, what would happen?

A The except block would run but print nothing

B The ValueError would be caught anyway

C The exception would be unhandled and stop the program

D The program would ignore the exception and continue

💡 Hint

Refer to concept_flow step 'Match exception type?--No' where unmatched exceptions are not handled

Concept Snapshot

try:
    # code that might fail
except SpecificError:
    # handle that error

- Runs try code
- If error matches except, runs handler
- Otherwise error propagates
- Program continues after handling

Full Transcript

This example shows how Python handles specific exceptions using try and except blocks. The program tries to convert a string to an integer. Since 'abc' is not a number, int('abc') raises a ValueError. The except block catches this ValueError and prints 'ValueError caught'. The variable x is never assigned because the error happens before assignment. After handling the exception, the program continues normally. If the except block was for a different error type, the ValueError would not be caught here and the program would stop with an error.