Multiple exception handling in Python - Step-by-Step Execution

Concept Flow - Multiple exception handling

Start try block

↓

Code runs

↓

Exception?

↓

v1

↓

Match exception type?

↓

v2

↓

Handle

↓

Continue after try-except

The program tries code, checks if an exception happens, then matches it to multiple except blocks to handle it or lets it propagate.

Execution Sample

Python

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

This code tries to convert a string to int, catches ValueError or TypeError separately.

Execution Table

Step	Action	Evaluation	Result
1	Enter try block	No exception yet	Proceed to next line
2	Execute x = int('abc')	Raises ValueError	Exception raised
3	Check except ValueError	Matches exception type	Handle ValueError
4	Execute print('ValueError caught')	Prints message	Output: ValueError caught
5	Exit try-except	Handled exception	Continue program
6	End	No more code	Program ends

💡 Exception ValueError caught by first except block, program continues normally

Variable Tracker

Variable	Start	After Step 2	After Step 5
x	undefined	Exception raised, no assignment	undefined

Key Moments - 2 Insights

Why doesn't the second except block for TypeError run?

Because the exception raised is ValueError, which matches the first except block (see step 3 in execution_table), so Python handles it there and skips the rest.

What happens if no except block matches the exception?

The exception propagates and stops the program unless caught elsewhere. This is shown in the flow where unmatched exceptions go to 'Unhandled -> propagate'.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 4?

A TypeError caught

B No output

C ValueError caught

D Program crashes

💡 Hint

Check the 'Result' column at step 4 in the execution_table.

At which step does the program decide which except block to run?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' and 'Evaluation' columns in execution_table step 3.

If the code raised a TypeError instead, which except block would run?

A TypeError except block

B No except block, program crashes

C ValueError except block

D Both except blocks

💡 Hint

Refer to the except blocks in the code sample and how exceptions match types.

Concept Snapshot

try:
  code that may raise exceptions
except ExceptionType1:
  handle ExceptionType1
except ExceptionType2:
  handle ExceptionType2

Python checks exceptions in order and runs the first matching except block.

Full Transcript

This example shows how Python runs code inside a try block and watches for exceptions. If an exception happens, Python looks at each except block in order to find one that matches the exception type. When it finds a match, it runs that except block's code and then continues the program normally. If no except block matches, the program stops with an error. In the example, converting 'abc' to int raises a ValueError, which is caught by the first except block. The second except block for TypeError is ignored because the exception type does not match. This way, multiple exceptions can be handled separately and clearly.