Learn Concatenation, Repetition, and Basic Formatting

You often need to build messages from pieces (names, numbers, results). Python gives you three core tools: + to glue a few strings, * to repeat a string, and f-strings to format values neatly. When joining many pieces (e.g., a list of words), use str.join.

Concatenation with `+`

Use + to join a small number of strings. If you need to combine text with numbers, convert the number or use an f-string.


              1234567
            
first = "Hello"
second = "world"
msg = first + " " + second           # "Hello world"

score = 10
# "score: " + score        # TypeError
msg2 = "score: " + str(score)        # OK: "score: 10"

Repetition with `*`

Multiply a string by an integer to repeat it.


              12
            
echo = "ha" * 3          # "hahaha"
rule = "-" * 10          # "----------"

Joining many pieces with `"sep".join(...)`

join is ideal when you have an iterable (like a list) of strings.


              12345
            
words = ["Python", "is", "fun"]
sentence = " ".join(words)            # "Python is fun"

lines = ["ID: 42", "OK", "Done"]
block = "\n".join(lines)              # "ID: 42\nOK\nDone"

Basic formatting with f-strings

An f-string evaluates expressions inside {} and inserts the result. It’s concise and handles type conversion automatically.


              123
            
name = "Ada"
tasks = 3
print(f"{name} completed {tasks} tasks.")   # "Ada completed 3 tasks."

Numeric formatting (common cases).


              1234
            
price = 12.5
tax = 0.2
total = price * (1 + tax)
print(f"Total: {total:.2f}")   # 2 decimal places, e.g., "Total: 15.00"

If you need a literal brace, double it.


              1
            
print(f"Use {{}} for placeholders.")  # "Use {} for placeholders."

Note

For long loops that build big strings, collect pieces and then ''.join(pieces) (you saw why in the immutability chapter).

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Section 3. Chapter 5

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Concatenation with `+`

Use + to join a small number of strings. If you need to combine text with numbers, convert the number or use an f-string.


              1234567
            
first = "Hello"
second = "world"
msg = first + " " + second           # "Hello world"

score = 10
# "score: " + score        # TypeError
msg2 = "score: " + str(score)        # OK: "score: 10"

Repetition with `*`

Multiply a string by an integer to repeat it.


              12
            
echo = "ha" * 3          # "hahaha"
rule = "-" * 10          # "----------"

Joining many pieces with `"sep".join(...)`

join is ideal when you have an iterable (like a list) of strings.


              12345
            
words = ["Python", "is", "fun"]
sentence = " ".join(words)            # "Python is fun"

lines = ["ID: 42", "OK", "Done"]
block = "\n".join(lines)              # "ID: 42\nOK\nDone"

Basic formatting with f-strings

An f-string evaluates expressions inside {} and inserts the result. It’s concise and handles type conversion automatically.


              123
            
name = "Ada"
tasks = 3
print(f"{name} completed {tasks} tasks.")   # "Ada completed 3 tasks."

Numeric formatting (common cases).


              1234
            
price = 12.5
tax = 0.2
total = price * (1 + tax)
print(f"Total: {total:.2f}")   # 2 decimal places, e.g., "Total: 15.00"

If you need a literal brace, double it.


              1
            
print(f"Use {{}} for placeholders.")  # "Use {} for placeholders."

Note

For long loops that build big strings, collect pieces and then ''.join(pieces) (you saw why in the immutability chapter).

Everything was clear?

Thanks for your feedback!

Section 3. Chapter 5

Concatenation, Repetition, and Basic Formatting

Concatenation with `+`

Repetition with `*`

Joining many pieces with `"sep".join(...)`

Basic formatting with f-strings

1. You have `items = ["red", "green", "blue"]`. Which is the best way to produce `"red, green, blue"`?

2. What does `"ha" * 2 + "!"` produce?

3. Which line prints a price with two decimal places if `total = 7.5`?

Awesome!

Concatenation, Repetition, and Basic Formatting

Concatenation with `+`

Repetition with `*`

Joining many pieces with `"sep".join(...)`

Basic formatting with f-strings

1. You have `items = ["red", "green", "blue"]`. Which is the best way to produce `"red, green, blue"`?

2. What does `"ha" * 2 + "!"` produce?

3. Which line prints a price with two decimal places if `total = 7.5`?

Concatenation, Repetition, and Basic Formatting

Concatenation with +

Repetition with *

Joining many pieces with "sep".join(...)

Basic formatting with f-strings

1. You have items = ["red", "green", "blue"]. Which is the best way to produce "red, green, blue"?

2. What does "ha" * 2 + "!" produce?

3. Which line prints a price with two decimal places if total = 7.5?

Awesome!

Concatenation, Repetition, and Basic Formatting

Concatenation with +

Repetition with *

Joining many pieces with "sep".join(...)

Basic formatting with f-strings

1. You have items = ["red", "green", "blue"]. Which is the best way to produce "red, green, blue"?

2. What does "ha" * 2 + "!" produce?

3. Which line prints a price with two decimal places if total = 7.5?

Concatenation with `+`

Repetition with `*`

Joining many pieces with `"sep".join(...)`

1. You have `items = ["red", "green", "blue"]`. Which is the best way to produce `"red, green, blue"`?

2. What does `"ha" * 2 + "!"` produce?

3. Which line prints a price with two decimal places if `total = 7.5`?

Concatenation with `+`

Repetition with `*`

Joining many pieces with `"sep".join(...)`

1. You have `items = ["red", "green", "blue"]`. Which is the best way to produce `"red, green, blue"`?

2. What does `"ha" * 2 + "!"` produce?

3. Which line prints a price with two decimal places if `total = 7.5`?