12. Strings

Strings are the values you print most. Python has a rich set of tools for them built directly onto string objects: joining, measuring, changing case, repeating, and formatting numbers into them. This chapter covers the ones you use daily.

Joining strings with + and f-strings

You can join two strings with + (the concatenation operator). It returns one new string with the second stuck onto the end of the first:

first = "Hello, "
second = "world!"
print(first + second)   # Hello, world!

The original variables are untouched — + builds a new string.

Python's + does not automatically convert numbers to strings. Adding a number to a string is an error:

level = 7
# print("Level " + level)   # TypeError: can only concatenate str to str

The fix is to wrap the number in str(), or use an f-string, which is the preferred Python approach:

level = 7
print("Level " + str(level) + " complete")   # Level 7 complete
print(f"Level {level} complete")              # Level 7 complete

An f-string starts with the letter f before the opening quote. Any expression inside {} is evaluated and inserted into the string. F-strings handle numbers, booleans, and any other type automatically.

Length with len

The len() function returns a string's length in characters:

print(len("hello"))        # 5
print(len(""))             # 0
greeting = "Welcome"
print(len(greeting))       # 7

Use len() whenever you need a string's length — for centring text, checking input length, or building borders.

Changing case

String methods live directly on string objects, called with a dot. Two simple ones are .upper() and .lower(). Both return a new string and leave the original alone:

name = "Keiko"
print(name.upper())   # KEIKO
print(name.lower())   # keiko
print(name)            # Keiko  (still the original)

Repeating a string

Multiplying a string by an integer with * repeats it that many times:

print("-" * 20)                        # --------------------
print("ab" * 3)                        # ababab
print("=" * 4 + " TITLE " + "=" * 4)  # ==== TITLE ====

It is the right tool for drawing borders or padding text.

Formatting with f-strings

When you need numbers or text plugged into specific spots, f-strings are the standard approach. Place any expression inside {}:

name = "Keiko"
level = 7
hp = 95
print(f"{name} (Lv {level}) HP {hp}")
# Keiko (Lv 7) HP 95

For control over decimal places and number formatting, add a format specification after a colon inside the braces:

price = 3.14159
print(f"Price: {price:.2f}")   # Price: 3.14

Escape sequences

Some characters are awkward in a string because they collide with Python's punctuation. The fix is an escape sequence — a backslash \ followed by a letter, which Python replaces with the special character:

Example:

print("Line 1\nLine 2\nLine 3")
# Line 1
# Line 2
# Line 3

print("Name\tLevel\tHP")
# Name    Level   HP

print("She said \"hi\" and waved.")
# She said "hi" and waved.

Multi-line strings

When a string spans many lines with lots of quotes, escape sequences get noisy. Python offers triple-quoted strings: """ to open and """ to close (or ''' and '''). Anything between them is the string, including newlines and quotes:

poem = """
Roses are red,
Violets are blue,
"Pick a number,"
said the program to you.
"""

print(poem)

Once created, triple-quoted strings are just regular strings — a friendlier way to write them.

Homework

Keiko  Lv 7   HP 95

----- INVENTORY -----
Inside text goes here
----- INVENTORY -----

Stuck or finished? Open the homework solutions page.