Working with text

Names, messages, answers to questions: most programs handle a lot of text. In Python, text is a string (str), written inside quotes.

city = "Kathmandu"
print(city)

The + operator joins two strings into one. This is called concatenation. It does not add spaces for you:

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

AdaLovelace
Ada Lovelace

+ only joins strings with strings. "Age: " + 12 causes a TypeError. You can convert a number to a string with str(12), but there is an easier way.

Put the letter f before the opening quote and you can drop variables straight into the text using curly brackets:

name = "Sam"
age = 12
print(f"{name} is {age} years old")
print(f"Next year {name} will be {age + 1}")

Sam is 12 years old
Next year Sam will be 13

Anything inside the curly brackets is worked out first, so you can do sums there too. f-strings are the most common way to build messages in Python.

Strings come with built-in tools called methods. You call a method by putting a dot after the string:

word = "python"
print(word.upper())
print(word.capitalize())
print("  hello  ".strip())
print("I like cats".replace("cats", "dogs"))

PYTHON
Python
hello
I like dogs

Methods give you a new string. They do not change the original, so word is still "python" afterwards.

len tells you how many characters a string has, spaces included:

print(len("Hello"))

5

Each character has a position, called its index. Counting starts at 0, not 1. Square brackets pick out a character:

word = "Python"
print(word[0])
print(word[1])
print(word[-1])

P
y
n

A negative index counts from the end, so word[-1] is the last character. You can also take a slice: word[0:3] gives the characters at positions 0, 1 and 2, which is "Pyt".