Strings

Text is everywhere — names, messages, file contents, user input. Python's str type is rich and pleasant to work with once you know the core moves.

Indexing and slicing

A string is a sequence of characters, accessible by position (starting at 0), and sliceable with [start:stop] (stop is exclusive — the half-open convention again):

word = "Python"
word[0]      # "P"
word[-1]     # "n"  (negative counts from the end)
word[0:3]    # "Pyt"
word[3:]     # "hon"

Strings are immutable — these operations return new strings; the original is never changed.

Useful methods

Strings come with a toolbox of methods that each return a new string or value:

"  hi  ".strip()        # "hi"      (remove surrounding whitespace)
"Hello".lower()          # "hello"
"a,b,c".split(",")       # ["a", "b", "c"]
"-".join(["a", "b"])     # "a-b"
"hello".replace("l", "L")# "heLLo"
"42".isdigit()           # True

f-strings: the way to build text

To insert values into text, use an f-string — prefix the string with f and put expressions in { }:

name = "Ada"
age = 36
f"{name} is {age}"            # "Ada is 36"
f"next year: {age + 1}"       # "next year: 37"  (any expression works)

f-strings are clearer and less error-prone than gluing strings together with + (and they sidestep the str + int TypeError from the types lesson).

Where to go next

Next: lists and tuples — ordered collections for holding many values.