String Concatenation and Repetition

What You'll Learn

Building strings with the + (concatenation) operator
Repeating strings with the * operator
When to use concatenation vs. f-strings vs. commas in print()
The += operator for building strings incrementally
Practical string-building patterns

1. String Concatenation Revisited

Concatenation: Joining two or more strings end-to-end using the + operator to create a new string.

We introduced concatenation briefly in Module 2. Now let us explore it more deeply:

first = "Hello"
second = "World"

# Simple concatenation
result = first + second
print(result)

# With a space in between
result = first + " " + second
print(result)

# Building a longer string
greeting = first + " " + second + "!" + " How are you?"
print(greeting)

HelloWorld Hello World Hello World! How are you?

Remember: Concatenation does NOT add spaces automatically. You must include them yourself. Compare this with print() using commas, which adds spaces for you.

2. Concatenation Requires Strings

The + operator can only join strings with other strings. If you try to concatenate a string with a number, Python raises a TypeError:

name = "Alice"
age = 25

# This will cause a TypeError!
# message = "Age: " + age

# Solution 1: Convert with str()
message = "Age: " + str(age)
print(message)

# Solution 2: Use an f-string (usually better)
message = f"Age: {age}"
print(message)

# Solution 3: Use commas in print()
print("Age:", age)

Age: 25 Age: 25 Age: 25

3. String Repetition with *

The * operator repeats a string a specified number of times:

# Basic repetition
print("Ha" * 3)
print("- " * 10)
print("=" * 40)

HaHaHa - - - - - - - - - - ========================================

Repetition is especially useful for creating visual separators and borders:

Creating a Bordered Title

title = "MY REPORT"
width = 30

print("+" + "-" * (width - 2) + "+")
print("|" + title.center(width - 2) + "|")
print("+" + "-" * (width - 2) + "+")

+----------------------------+ | MY REPORT | +----------------------------+

Simple Text Art

print("  *")
print(" ***")
print("*****")
print("  |")

* *** ***** |

4. Building Strings with +=

The += operator appends text to an existing string:

message = "Hello"
message += ", "
message += "World"
message += "!"
print(message)

Hello, World!

Building a List of Items

shopping_list = "Shopping List:\n"
shopping_list += "- Apples\n"
shopping_list += "- Bread\n"
shopping_list += "- Milk\n"
shopping_list += "- Eggs"

print(shopping_list)

Shopping List: - Apples - Bread - Milk - Eggs

5. When to Use Which Approach

Python offers several ways to combine text and values. Here is when to use each:

f-strings -- Best for mixing variables and text. Use this as your default choice.

print(f"Hello, {name}! You are {age} years old.")

Commas in print() -- Best for quick debugging or when you just want to display values.

print("Name:", name, "Age:", age)

Concatenation (+) -- Best when building strings to store in variables, or joining a small number of strings.

full_name = first_name + " " + last_name

Repetition (*) -- Best for creating visual patterns or repeating content.

border = "=" * 40

Pro Tip: In most situations, f-strings are the cleanest and most readable option. Use them as your go-to choice. Save concatenation for when you need to build a string variable over multiple steps.

6. Practical Example: A Complete Program

# A program that combines everything from Module 3
name = input("Enter your name: ")
hours = float(input("Hours worked this week: "))
rate = float(input("Hourly rate: $"))

gross_pay = hours * rate
tax_rate = 0.15
taxes = gross_pay * tax_rate
net_pay = gross_pay - taxes

# Formatted output using multiple techniques
border = "=" * 35
print()
print(border)
print(f"  Pay Stub for {name}")
print(border)
print(f"  Hours Worked:  {hours}")
print(f"  Hourly Rate:   ${rate:.2f}")
print(f"  Gross Pay:     ${gross_pay:,.2f}")
print(f"  Taxes ({tax_rate:.0%}):   ${taxes:,.2f}")
print("-" * 35)
print(f"  Net Pay:       ${net_pay:,.2f}")
print(border)

Check Your Understanding

Question 1: What is the output of "abc" + "def"?

Answer: "abcdef" -- concatenation joins strings with no space.

Question 2: What is the output of "Ha" * 4?

Answer: "HaHaHaHa"

Question 3: When should you use f-strings instead of concatenation?

Answer: Use f-strings when mixing variables and text. They are more readable and do not require str() conversion. Use concatenation for simple string joining or building strings incrementally with +=.

Try It Yourself!

Build a full name from first, middle, and last name variables using concatenation.
Create a decorative border using * repetition around a message.
Write a program that asks for a user's name and creates a personalized greeting card using borders and f-strings.

Key Takeaways

+ concatenates strings (no automatic spaces).
* repeats a string a given number of times.
Concatenation requires all parts to be strings -- use str() to convert numbers.
+= appends text to an existing string variable.
f-strings are usually the best choice for mixing text and variables.
Use commas in print() for quick output with automatic spaces.
Use concatenation when building strings to store in variables.
Use repetition for visual patterns and separators.

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