Data Structures

>Data Structures — cheat sheet

Choose the right collection to organize values, text, and named information in your programs.

Lists

colors = ["red", "green", "blue"]

Lists keep ordered values in square brackets.

print(colors[0], colors[-1])

Index 0 is first; index -1 is last.

colors.append("purple")
colors.insert(1, "yellow")

Add one item at the end or at an index.

colors.remove("green")
last_color = colors.pop()

Remove a matching item or remove and return the last one.

ordered = sorted([8, 3, 5])

sorted returns a new sorted list.

scores = [8, 3, 5]
scores.sort()

sort changes the existing list.

scores.reverse()

reverse changes the existing list order.

copy_scores = scores.copy()

copy makes a separate shallow list.

point = (3, 5)
print(point[1])

Tuples are ordered values that cannot be changed.

one_item = ("hello",)

A one-item tuple needs a trailing comma.

name, age = ("Mina", 14)

Unpack tuple values into separate names.

clean = "  Hello  ".strip().lower()

String methods return new text because strings are immutable.

print("Python"[1:4])

Slice text from a start index up to, not including, an end index.

words = "red,blue".split(",")

split turns text into a list of strings.

label = " | ".join(["red", "blue"])

join combines strings with a chosen separator.

print("banana".find("na"))

find returns the first position or -1.

colors = {"red", "blue", "red"}
colors.add("green")

Sets keep unique values and support add.

print({1, 2, 3} & {3, 4})

& finds values shared by two sets.

student = {"name": "Ivy"}
print(student.get("level", "beginner"))

get returns a fallback for a missing dictionary key.

squares = [number * number for number in [1, 2, 3]]

A list comprehension transforms every item concisely.