Multiple rescue clauses in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of multiple rescue clauses with different exceptions

What is the output of this Ruby code with multiple rescue clauses?

Ruby

begin
  1 / 0
rescue ZeroDivisionError
  puts "ZeroDivisionError caught"
rescue StandardError
  puts "StandardError caught"
end

A StandardError caught

B ZeroDivisionError caught

C No output, program crashes

D RuntimeError caught

💡 Hint

Think about which error is raised by dividing by zero in Ruby.

Dividing by zero raises a ZeroDivisionError, so the first rescue clause matches and prints "ZeroDivisionError caught".

❓ Predict Output

intermediate

Which rescue clause handles the exception?

What will this Ruby code print?

Ruby

begin
  [].fetch(10)
rescue IndexError
  puts "IndexError handled"
rescue KeyError
  puts "KeyError handled"
end

A KeyError handled

B ArgumentError handled

C No output, program crashes

D IndexError handled

💡 Hint

Check what exception is raised when fetching an invalid index from an array.

Calling fetch with an invalid index raises IndexError, so the first rescue clause runs.

❓ Predict Output

advanced

Output when multiple exceptions are rescued with one clause

What does this Ruby code output?

Ruby

begin
  {}.fetch(:foo)
rescue KeyError, NoMethodError
  puts "KeyError or NoMethodError rescued"
rescue StandardError
  puts "StandardError rescued"
end

A KeyError or NoMethodError rescued

B StandardError rescued

C No output, program crashes

D TypeError rescued

💡 Hint

Accessing a missing key in a hash with [] returns nil, but with fetch it raises KeyError.

Hash#fetch raises KeyError for missing keys, so the first rescue clause matches and prints "KeyError or NoMethodError rescued".

❓ Predict Output

advanced

Which rescue clause runs with nested exceptions?

What will this Ruby code print?

Ruby

begin
  begin
    raise ArgumentError, "wrong argument"
  rescue TypeError
    puts "TypeError rescued"
  end
rescue ArgumentError
  puts "ArgumentError rescued"
end

A No output, program crashes

B TypeError rescued

C ArgumentError rescued

D RuntimeError rescued

💡 Hint

The inner rescue only catches TypeError, but the raised error is ArgumentError.

The inner rescue does not catch ArgumentError, so it propagates to the outer rescue which catches ArgumentError and prints "ArgumentError rescued".

❓ Predict Output

expert

Output of multiple rescue clauses with else and ensure

What is the output of this Ruby code?

Ruby

begin
  puts "Start"
  10 / 2
rescue ZeroDivisionError
  puts "ZeroDivisionError caught"
rescue StandardError
  puts "StandardError caught"
else
  puts "No errors"
ensure
  puts "Always runs"
end

A

Start
No errors
Always runs

B

Start
ZeroDivisionError caught
Always runs

C

Start
Always runs

D

Start
StandardError caught
Always runs

💡 Hint

The else clause runs only if no exception is raised.

The division 10 / 2 does not raise an error, so the else clause runs printing "No errors". The ensure clause always runs printing "Always runs".

Practice

1. What is the purpose of using multiple rescue clauses in Ruby?

easy

A. To repeat the same error handling multiple times

B. To run code only when no errors occur

C. To handle different types of errors with specific responses

D. To skip error handling entirely

Solution

1. Step 1: Understand rescue clauses

   Multiple rescue clauses allow you to catch different error types separately.

2. Step 2: Purpose of specific error handling

   This helps you respond differently depending on the error type.

3. Final Answer:

   To handle different types of errors with specific responses -> Option C

4. Quick Check:

   Multiple rescue clauses = specific error handling [OK]

Hint: Multiple rescue clauses catch different errors separately [OK]

Common Mistakes:

• Thinking rescue clauses run only when no errors occur
• Assuming multiple rescue repeats same handling
• Believing rescue skips error handling

2. Which of the following is the correct syntax for multiple rescue clauses in Ruby?

easy

A. try
# code
rescue ZeroDivisionError
# handle zero division
rescue StandardError
# handle other errors
end

B. begin
# code
catch ZeroDivisionError
# handle zero division
catch StandardError
# handle other errors
end

C. begin
# code
rescue ZeroDivisionError, StandardError
# handle errors
end

D. begin
# code
rescue ZeroDivisionError
# handle zero division
rescue StandardError
# handle other errors
end

Solution

1. Step 1: Identify Ruby error handling syntax

   Ruby uses begin and rescue for error handling, not try or catch.

2. Step 2: Check multiple rescue clauses

   Multiple rescue clauses are written one after another inside begin...end.

3. Final Answer:

   begin # code rescue ZeroDivisionError # handle zero division rescue StandardError # handle other errors end -> Option D

4. Quick Check:

   Ruby uses begin-rescue-end with multiple rescue [OK]

Hint: Use begin-rescue-end blocks for multiple error types [OK]

Common Mistakes:

• Using try or catch instead of rescue
• Combining errors in one rescue without comma
• Incorrect block keywords

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

begin
  1 / 0
rescue ZeroDivisionError
  puts 'Zero division error caught'
rescue StandardError
  puts 'Standard error caught'
end

medium

A. Zero division error caught

B. Standard error caught

C. No output, program crashes

D. SyntaxError

Solution

1. Step 1: Identify the error raised

   The code 1 / 0 raises a ZeroDivisionError.

2. Step 2: Match error with rescue clauses

   The first rescue clause catches ZeroDivisionError and prints the message.

3. Final Answer:

   Zero division error caught -> Option A

4. Quick Check:

   ZeroDivisionError triggers first rescue [OK]

Hint: Match error type to first rescue clause that fits [OK]

Common Mistakes:

• Assuming StandardError rescue runs first
• Thinking program crashes without rescue
• Confusing syntax error with runtime error

4. Identify the error in this Ruby code with multiple rescue clauses:

begin
  puts 'Start'
rescue
  puts 'Rescue block'
rescue ZeroDivisionError
  puts 'Zero division error'
end

medium

A. Missing ensure block causes error

B. Multiple rescue clauses after a generic rescue cause syntax error

C. No error, code runs fine

D. Rescue clauses must be inside methods only

Solution

1. Step 1: Check for syntax errors

   In Ruby, a generic rescue clause must come after all specific rescue clauses. Placing a generic rescue before specific ones causes a syntax error.

2. Step 2: Analyze the code

   The code places a generic rescue first, then a specific rescue, which is invalid syntax.

3. Final Answer:

   Multiple rescue clauses after a generic rescue cause syntax error -> Option B

4. Quick Check:

   Generic rescue must be last [OK]

Hint: Generic rescue clause must come after specific rescue clauses [OK]

Common Mistakes:

• Thinking generic rescue before specific causes syntax error
• Believing ensure block is mandatory
• Assuming rescue clauses only work inside methods

5. Given this Ruby code, what will be printed?

def test
  begin
    raise ArgumentError, 'Wrong argument'
  rescue ZeroDivisionError
    puts 'Zero division error'
  rescue ArgumentError
    puts 'Argument error caught'
  ensure
    puts 'Always runs'
  end
end
test

hard

A. Argument error caught
Always runs

B. Zero division error
Always runs

C. Always runs
Argument error caught

D. No output, error not handled

Solution

1. Step 1: Identify raised error

   The code raises ArgumentError with message 'Wrong argument'.

2. Step 2: Match rescue clauses

   The ArgumentError rescue clause runs and prints 'Argument error caught'.

3. Step 3: Understand ensure block

   The ensure block always runs, printing 'Always runs'.

4. Final Answer:

   Argument error caught Always runs -> Option A

5. Quick Check:

   ArgumentError rescued, ensure always runs [OK]

Hint: Ensure block runs after rescue regardless of error [OK]

Common Mistakes:

• Thinking ensure runs before rescue
• Assuming wrong rescue clause runs
• Ignoring ensure block output