Working with Text (Strings)

Why this matters

A huge share of real-world data is text: names, messages, addresses, web pages. Python makes working with text pleasant.

The idea

You can combine and repeat strings:

first = "Ada"
last = "Lovelace"
print(first + " " + last)   # Ada Lovelace   (+ joins text: "concatenation")
print("ha" * 3)             # hahaha
print(len("hello"))         # 5   (len() counts characters)

Each character has a position called an index, starting at 0. Negative numbers count from the end:

word = "python"
print(word[0])    # p
print(word[2])    # t
print(word[-1])   # n   (the last character)

Strings come with methods: actions you call with a dot after the value.

text = "  Hello, World  "
print(text.strip())     # Hello, World   (removes spaces at both ends)
print(text.upper())     # "  HELLO, WORLD  "
print(text.lower())     # "  hello, world  "
print("ada lovelace".title())      # Ada Lovelace
print("a-b-c".replace("-", "+"))   # a+b+c

Methods do not change the original string; they give you a new one. To keep the result, store it: text = text.strip(). You can chain methods: name.strip().title().

Try it

Experiment: print len("hello world"), "hello"[1], "hello"[-2], and "hello".upper(). What happens with "hello"[10]? Read the error.

Your turn

The starter program reads a name that might be messy: extra spaces, odd capital letters. Write a program that

1. cleans the name (no spaces at the ends, each word capitalised) and prints it, then
2. prints how many characters the cleaned name has.

For the input aDa LoVElace it must print:

Ada Lovelace
Length: 12

Recap

• + joins strings, * repeats them, len() counts characters.
• Indexes start at 0; negative indexes count from the end.
• String methods like strip(), upper(), lower(), title() and replace() return new strings.

Common mistakes

• Mixing text and numbers with +: "Age: " + 30 is a TypeError. Convert with str(30) (the next lesson has a nicer way).
• Starting to count at 1. The first character is index 0.
• Forgetting the brackets: name.strip (no parentheses) does not call the method.