String concatenation and repetition in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of repeated string concatenation

What is the output of this Python code?

Python

s = 'ab'
result = s * 3 + 'cd'
print(result)

A "abcdabcdabcd"

B "ababab"

C "abababcd"

D "ababcdcdcd"

💡 Hint

Remember that multiplying a string repeats it, and + adds strings together.

The string 'ab' repeated 3 times is 'ababab'. Adding 'cd' at the end gives 'abababcd'.

❓ Predict Output

intermediate

Result of mixed string operations

What does this code print?

Python

a = 'x'
b = 'y'
print((a + b) * 2)

A "xyxy"

B "xxyy"

C "xy2"

D "x2y2"

💡 Hint

The parentheses affect the order of operations.

The expression (a + b) creates 'xy'. Multiplying by 2 repeats it twice: 'xyxy'.

❓ Predict Output

advanced

Output of string repetition with variables

What is the output of this code?

Python

word = 'go'
count = 4
print(word * count + word)

A "gogogogogog"

B "gogogogo"

C "gogogo4"

D "gogogogogo"

💡 Hint

Multiplying a string by a number repeats it that many times.

word * count repeats 'go' 4 times: 'gogogogo'. Adding 'go' once more results in 'gogogogogo'.

❓ Predict Output

advanced

String concatenation with different types

What happens when you run this code?

Python

s = 'num'
n = 3
print(s + n * 2)

A TypeError

B "numnum"

C "num6"

D "num3num3"

💡 Hint

You cannot add a string and an integer directly.

Trying to add a string and an integer causes a TypeError in Python.

🧠 Conceptual

expert

Understanding string repetition and concatenation order

Given the code below, what is the value of variable result?

Python

result = 'a' + 'b' * 2 + 'c' * 3

A "ab2c3"

B "abbccc"

C "aabcc"

D "abcabcabc"

💡 Hint

Multiplication repeats the string before concatenation.

The code repeats 'b' twice to get 'bb' and 'c' three times to get 'ccc'. Adding 'a' at the start results in 'abbccc'.

Practice

1. What does the + operator do when used with strings in Python?

easy

A. Joins two strings together into one

B. Repeats the string multiple times

C. Converts the string to uppercase

D. Splits the string into a list

Solution

1. Step 1: Understand the + operator with strings

   In Python, + combines two strings by joining them end to end.

2. Step 2: Compare with other options

   Repeating strings uses *, uppercase uses .upper(), splitting uses .split().

3. Final Answer:

   Joins two strings together into one -> Option A

4. Quick Check:

   String + String = Joined String [OK]

Hint: Remember: + joins strings, * repeats strings [OK]

Common Mistakes:

• Confusing + with * for repetition
• Thinking + changes string case
• Assuming + splits strings

2. Which of the following is the correct syntax to repeat the string 'hi' 3 times in Python?

easy

A. 'hi' + 3

B. 'hi' * 3

C. 3 'hi'

D. 'hi' ** 3

Solution

1. Step 1: Identify the repetition operator

   In Python, * repeats a string when multiplied by an integer.

2. Step 2: Check other options

   'hi' + 3 causes TypeError (can't add string and int). 3 'hi' is SyntaxError (missing * operator). 'hi' ** 3 causes TypeError (** is for exponents, not string repetition).

3. Final Answer:

   'hi' * 3 -> Option B

4. Quick Check:

   String * Number = Repeated String [OK]

Hint: Use * between string and number to repeat [OK]

Common Mistakes:

• Using + instead of * for repetition
• Trying to use ** which is invalid for strings
• Placing number before string without *

3. What is the output of the following code?

result = 'ab' + 'cd' * 2
print(result)

medium

A. abcdabcd

B. ababcd

C. abcdcdcd

D. abcdcd

Solution

1. Step 1: Evaluate the repetition part

   'cd' * 2 repeats 'cd' twice, resulting in 'cdcd'.

2. Step 2: Concatenate strings

   'ab' + 'cdcd' joins to form 'abcdcd'.

3. Final Answer:

   abcdcd -> Option D

4. Quick Check:

   'ab' + ('cd' * 2) = 'abcdcd' [OK]

Hint: Calculate repetition first, then join strings [OK]

Common Mistakes:

• Adding strings before repeating
• Repeating the whole concatenated string
• Miscounting repeated parts

4. Find the error in this code snippet:

text = 'go' * '3'
print(text)

medium

A. TypeError because string cannot be multiplied by string

B. SyntaxError due to missing parentheses

C. NameError because 'text' is undefined

D. No error, prints 'gogogo'

Solution

1. Step 1: Identify the operands of the * operator

   The code tries to multiply a string 'go' by another string '3'.

2. Step 2: Understand Python's type rules for * operator

   Python allows string * integer but not string * string, causing a TypeError.

3. Final Answer:

   TypeError because string cannot be multiplied by string -> Option A

4. Quick Check:

   String * String = TypeError [OK]

Hint: Multiply string only by integer, not by string [OK]

Common Mistakes:

• Using quotes around number for repetition
• Assuming implicit conversion to int
• Ignoring error messages

5. You want to create a string that repeats the word 'yes' 4 times, separated by a dash -. Which code produces 'yes-yes-yes-yes'?

hard

A. 'yes' + '-' * 3

B. 'yes-' * 4

C. ('yes-' * 4)[:-1]

D. '-'.join('yes' * 4)

Solution

1. Step 1: Understand the desired output

   The string should be 'yes-yes-yes-yes' with 3 dashes separating 4 'yes'.

2. Step 2: Analyze each option

   ('yes-' * 4)[:-1] repeats 'yes-' 4 times: 'yes-yes-yes-yes-' then removes last dash with [:-1]. 'yes-' * 4 leaves trailing dash. '-'.join('yes' * 4) joins characters, not words. 'yes' + '-' * 3 adds only one dash.

3. Final Answer:

   ('yes-' * 4)[:-1] -> Option C

4. Quick Check:

   Repeat with dash, then remove last dash [OK]

Hint: Repeat with dash, then remove last dash [OK]

Common Mistakes:

• Leaving extra dash at end
• Joining characters instead of words
• Adding fewer dashes than needed