Reading data: cheat sheet

Data detective · In any playground, open Reference to copy these.

Start the total at 0 once, then add to it on every pass.

total = 0
while total < 10:
    total += int(input("Add: "))

Give a value a name, so you can reuse and change it.

size = 50

Example

length = 120
forward(length)
left(90)
forward(length / 2)

Work through a list, one item at a time.

for c in colours:
    pass

Example

pensize(6)
for c in ["red", "blue", "green"]:
    pencolor(c)
    forward(40)

Show text or a value in the output box.

print("Hello")

Values stored under names (keys). One dictionary can hold everything about one thing.

star = {"speed": 5, "points": 1}

True if the item is in the list (or the key is in the dictionary, or the letters are in the text).

if item in bag:
    pass

Each row of the file becomes a dictionary, keyed by the column names in the first line. Every value is text.

import csv

with open("music.csv") as f:
    rows = list(csv.DictReader(f))

Do one thing or the other, depending on a condition.

if x > 0:
    pass
else:
    pass

Example

for x in [-90, -30, 30, 90]:
    penup()
    goto(x, 0)
    if x > 0:
        dot(30, "red")
    else:
        dot(30, "blue")
hideturtle()

Change a value every pass: read the old one, store a new one.

size = 5
for i in range(20):
    forward(size)
    right(90)
    size = size + 5

Example

size = 5
for i in range(30):
    forward(size)
    right(90)
    size = size + 5

Join pieces of text into one with +. Spaces only appear where they are inside the quotes.

"Hello, " + name

The value stored under that key. The key goes in quotes. Assign to it to change it: star["speed"] = 8.

star["speed"]

Opens the file to read and gives you all of it as one piece of text.

with open("save.txt") as f:
    text = f.read()