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Getting Started with Python

Strings

Getting Started with Python 20 min read

Strings

Objectives

By the end of this chapter, you should be able to:

  • Use common string methods
  • Build strings with f-strings

💡 Why this matters: Strings handle almost all text input and output. You’ll use these methods in nearly every program you write.

Strings Are Iterable

A string is a sequence of characters, so you can loop over it like a list:

python
for x in "word":
    print(x)
# w
# o
# r
# d

Strings Are Immutable

You can’t change part of a string in place:

python
my_str = "can't touch this"
my_str[6] = " "  # TypeError

Every string method returns a brand new string. It never modifies the original:

python
greeting = "hi"
greeting.upper()  # 'HI'
greeting           # 'hi', unchanged

String Methods

Try each of these in a REPL on "this Is nIce":

Method Does Example
.upper() Uppercase everything "hi".upper() returns 'HI'
.lower() Lowercase everything "HI".lower() returns 'hi'
.capitalize() Uppercase first letter only "hi there".capitalize() returns 'Hi there'
.title() Uppercase first letter of every word "hi there".title() returns 'Hi There'
.find(x) Index of first match, -1 if not found "erin".find("e") returns 0
.isalpha() True if every character is a letter "hi".isalpha() returns True
.endswith(x) True if the string ends with x "string".endswith("g") returns True

.find() is case sensitive:

python
name = "erin"
name.find("e")  # 0
name.find("E")  # -1, no uppercase "E" in the string

Building Strings with f-strings

Joining variables with + gets messy fast:

python
first_name = "Jordan"
city = "San Francisco"

greeting = "Hi, my name is " + first_name + ". I live in " + city + "."

An f-string is cleaner. Put an f before the string, then reference any variable directly inside {}:

python
greeting = f"Hi, my name is {first_name}. I live in {city}."

This is the standard way to build strings in modern Python.

Try It

  1. Loop over any word, one character at a time, with a for loop.
  2. Take a string and predict what .upper(), .capitalize(), and .title() return, then run each to check.
  3. Build a sentence about yourself using an f-string with at least two variables.

Recap

  • Strings are iterable and immutable. Methods return a new string rather than modifying the original.
  • f-strings (f"...{variable}...") are the standard way to build strings from variables.

Next lesson: boolean logic, and controlling what your code actually does.