Text: working with strings

A string is text. Anything in quotes is a string, and Python gives you a surprising amount of power over them.

Quotes

Single or double quotes both work. Pick one and be consistent:

print('single quotes')
print("double quotes")

single quotes
double quotes

The choice matters in one situation — when the text itself contains a quote:

print("It's raining")
print('She said "hello"')

It's raining
She said "hello"

Wrap in the other kind of quote and you never need to think about it again.

Joining text together

Adding strings sticks them end to end:

first = "Ada"
last = "Lovelace"
print(first + last)
print(first + " " + last)

AdaLovelace
Ada Lovelace

Look at the first line. Python did exactly what you asked — it joined them with nothing in between. Spaces are not free. If you want one, you have to say so.

f-strings: the good way

Gluing strings with + gets ugly fast, especially with numbers mixed in. An f-string lets you drop values straight into the text. Put an f before the quote and wrap the values in { }:

name = "Ada"
age = 36

print(f"{name} is {age} years old")
print(f"Next year she will be {age + 1}")

Ada is 36 years old
Next year she will be 37

The second line shows the real power: you can do maths inside the braces. f-strings are how modern Python builds text — use them everywhere.

Useful things strings can do

Strings carry their own tools, reached with a dot:

shout = "hello there"

print(shout.upper())
print(shout.title())
print(shout.replace("there", "world"))
print(len(shout))

HELLO THERE
Hello There
hello world
11

len() is the odd one out — it wraps around the string instead of hanging off it with a dot. You'll meet len() again with lists.

The mistake nearly everyone makes

Methods return a new string. They do not change the original:

name = "ada"
name.upper()
print(name)

ada

Nothing happened — or so it looks. name.upper() produced "ADA" and then Python threw it away, because you never stored it. Strings in Python cannot be changed once made; you can only build new ones.

Store the result:

name = "ada"
name = name.upper()
print(name)

ADA

This trips up almost every beginner at least once. When a string method "doesn't work", check whether you kept what it gave back.

Text that looks like a number

From lesson 1: "13" and 13 are different things. Now you can convert:

answer = "42"
print(answer + "!")
print(int(answer) + 1)

42!
43

int() turns text into a number; str() goes the other way. Try answer + 1 and read the error — Python tells you plainly that it will not add a number to text.