Begin/rescue/end blocks in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a begin/rescue/end block in Ruby?

It is used to handle errors (exceptions) that might happen during the execution of code inside the begin block, allowing the program to continue running instead of crashing.

beginner

How do you catch a specific error type in a rescue block?

You specify the error class after <code>rescue</code>. For example: <code>rescue ZeroDivisionError</code> will catch only division by zero errors.

beginner

What happens if an error occurs inside a begin block but there is no matching rescue block?

The program will stop and show the error message (raise the exception) because it was not handled.

intermediate

Can you have multiple rescue clauses in one begin block? Why?

Yes, you can have multiple rescue clauses to handle different types of errors separately, making your error handling more precise.

intermediate

What is the role of the ensure block in Ruby's error handling?

The ensure block runs code no matter what happens in the begin block, whether an error occurs or not. It's useful for cleanup actions like closing files.

What keyword starts a block that handles exceptions in Ruby?

A try

B handle

C catch

D begin

In Ruby, begin starts a block where exceptions can be handled with rescue.

Which keyword is used to catch exceptions in Ruby?

A except

B catch

C rescue

D handle

rescue is used in Ruby to catch and handle exceptions.

What will happen if an exception is raised but no rescue block matches it?

A The program crashes and shows the error

B The program retries the code

C The program ignores the error

D The program logs the error silently

If no matching rescue block is found, Ruby raises the exception and the program stops.

Which block runs code regardless of whether an exception occurs or not?

A rescue

B ensure

C finally

D begin

ensure runs code no matter what, useful for cleanup.

How do you rescue multiple specific exceptions in one rescue clause?

A rescue Exception1, Exception2

B rescue Exception1 | Exception2

C rescue (Exception1, Exception2)

D rescue Exception1 & Exception2

You list exceptions separated by commas after rescue to catch multiple types.

Explain how a begin/rescue/end block works in Ruby and why it is useful.

Think about how you catch mistakes in real life to keep things running smoothly.

Describe the difference between rescue and ensure blocks in Ruby error handling.

One catches problems, the other always runs no matter what.

Practice

1. What is the purpose of the begin/rescue/end block in Ruby?

easy

A. To declare variables

B. To create a loop that repeats code

C. To define a new method

D. To handle errors and prevent the program from crashing

Solution

1. Step 1: Understand the role of begin block

   The begin block contains code that might cause an error.

2. Step 2: Understand the role of rescue block

   The rescue block catches errors and handles them so the program doesn't crash.

3. Final Answer:

   To handle errors and prevent the program from crashing -> Option D

4. Quick Check:

   begin/rescue = error handling [OK]

Hint: Remember: begin/rescue is for catching errors safely [OK]

Common Mistakes:

• Thinking begin/rescue creates loops
• Confusing rescue with method definition
• Using begin/rescue to declare variables

2. Which of the following is the correct syntax to handle exceptions using begin/rescue/end in Ruby?

easy

A. begin
risky_code
rescue
handle_error
end

B. try {
risky_code
} catch {
handle_error
}

C. if error then
handle_error
end

D. begin:
risky_code
except:
handle_error

Solution

1. Step 1: Identify Ruby syntax for error handling

   Ruby uses begin, rescue, and end keywords for exceptions.

2. Step 2: Compare options with Ruby syntax

   begin risky_code rescue handle_error end matches Ruby syntax exactly; others use syntax from other languages or incorrect keywords.

3. Final Answer:

   begin\n risky_code\nrescue\n handle_error\nend -> Option A

4. Quick Check:

   Ruby error handling = begin/rescue/end [OK]

Hint: Look for Ruby keywords: begin, rescue, end [OK]

Common Mistakes:

• Using try/catch like other languages
• Using if/else for error handling
• Mixing Python or JavaScript syntax

3. What will be the output of this Ruby code?

begin
  puts 10 / 0
rescue ZeroDivisionError
  puts "Cannot divide by zero"
end

medium

A. Cannot divide by zero

B. 0

C. 10

D. ZeroDivisionError

Solution

1. Step 1: Identify the error in the code

   The code tries to divide 10 by 0, which raises a ZeroDivisionError.

2. Step 2: Understand the rescue block

   The rescue block catches ZeroDivisionError and prints "Cannot divide by zero" instead of crashing.

3. Final Answer:

   Cannot divide by zero -> Option A

4. Quick Check:

   ZeroDivisionError caught = message printed [OK]

Hint: Divide by zero triggers rescue message [OK]

Common Mistakes:

• Expecting program to crash
• Thinking it prints 0 or 10
• Confusing error name with output

4. Find the error in this Ruby code snippet:

begin
  puts 5 + "3"
rescue
  puts "Error caught"
end

medium

A. The begin block should be replaced with try

B. The rescue block is missing the error type

C. You cannot add a number and a string directly

D. The code will run without errors

Solution

1. Step 1: Analyze the operation inside begin block

   Adding 5 (number) and "3" (string) causes a TypeError in Ruby.

2. Step 2: Check error handling

   The rescue block catches any error and prints "Error caught"; the error is due to incompatible types.

3. Final Answer:

   You cannot add a number and a string directly -> Option C

4. Quick Check:

   Type mismatch causes error caught [OK]

Hint: Check data types before adding values [OK]

Common Mistakes:

• Thinking rescue needs error type always
• Assuming code runs without error
• Confusing begin with try

5. How can you modify this code to handle multiple specific errors separately?

begin
  # risky code
rescue
  puts "An error occurred"
end

hard

A. Use if statements inside begin block

B. Use multiple rescue clauses with specific error classes

C. Replace rescue with else to catch errors

D. Put all code inside rescue block

Solution

1. Step 1: Understand handling multiple errors

   Ruby allows multiple rescue clauses to catch different error types separately.

2. Step 2: Apply multiple rescue clauses

   Write rescue clauses like rescue ZeroDivisionError and rescue IOError to handle errors distinctly.

3. Final Answer:

   Use multiple rescue clauses with specific error classes -> Option B

4. Quick Check:

   Multiple rescue = specific error handling [OK]

Hint: Use separate rescue for each error type [OK]

Common Mistakes:

• Using else instead of rescue
• Trying to catch errors with if statements
• Putting code inside rescue block