String concatenation and repetition in Python

Introduction

String concatenation lets you join words or sentences together. Repetition helps you repeat the same word or sentence multiple times easily.

When you want to join a first name and last name into a full name.

When you want to create a greeting message by joining 'Hello' and a person's name.

When you want to print a pattern like '***' by repeating a star character.

When you want to build a sentence by joining several smaller strings.

When you want to repeat a word multiple times for emphasis or decoration.

Syntax

Python

concatenation: string1 + string2
repetition: string * number

Use the plus sign (+) to join two or more strings together.

Use the asterisk (*) to repeat a string a certain number of times.

Examples

This joins 'John', a space, and 'Doe' to make 'John Doe'.

Python

full_name = "John" + " " + "Doe"
print(full_name)

This creates a greeting by joining 'Hi', a comma and space, and 'Alice!'.

Python

greeting = "Hi" + ", " + "Alice!"
print(greeting)

This repeats the star character 5 times to print '*****'.

Python

stars = "*" * 5
print(stars)

This repeats 'ha' three times to print 'hahaha'.

Python

laugh = "ha" * 3
print(laugh)

Sample Program

This program joins first and last names with a space, then repeats the word 'Wow! ' three times.

Python

first_name = "Emma"
last_name = "Brown"
full_name = first_name + " " + last_name
print("Full name:", full_name)

repeat_word = "Wow! " * 3
print("Repeated word:", repeat_word)

Important Notes

Remember to add spaces if you want spaces between words when concatenating.

Repetition only works with strings and a positive integer number.

Concatenation creates a new string; it does not change the original strings.

Summary

Use + to join strings together.

Use * to repeat a string multiple times.

Both help build new strings easily from smaller parts.

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