← Data detective

Data detective reference

Reading, counting, charting, cleaning and testing data in Python, then pandas and Gradio.

Print a cheat sheet (the whole course or one unit, with a picture of what each command draws)

Code structure

for i in range(4):
    pass

Example

for i in range(5):
    forward(15)
    penup()
    forward(10)
    pendown()
for loop

Repeat the indented lines this many times.

What the example draws
range(5): five dashes

id: for-loop

while True:
    pass

Example

r = 10
while r < 60:
    circle(r)
    r = r + 15
while loop

Repeat the indented lines for as long as the condition is true.

What the example draws
A circle each time, while r < 60

id: while-loop

name = input("What is your name? ")
print("Hello, " + name)

Example

name = input("What is your name? ")
print("Hello, " + name)
ask and reply

Ask a question, store the typed answer, and use it in a reply.

What the example draws
Asks for a name, then says hello

id: ask-and-reply

text = input("How many? ")
if text.isdigit():
    number = int(text)
    pass
else:
    print("Please type a number.")

Example

text = input("How many tickets? ")
if text.isdigit():
    print("That will be $" + str(int(text) * 12) + ".")
else:
    print("Please type a number.")
check then convert

Check typed text with isdigit before turning it into a number.

What the example draws
A checked ticket total

id: check-then-convert

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

Example

total = 0
while total < 10:
    total += int(input("Add: "))
    print("Total: " + str(total))
print("Done")
running total

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

id: running-total

while True:
    choice = input("1 add, 2 quit: ")
    if choice == "1":
        pass
    elif choice == "2":
        break
    else:
        print("Please choose 1 or 2.")

Example

total = 0
while True:
    choice = input("1 add $5, 2 pay: ")
    if choice == "1":
        total += 5
    elif choice == "2":
        break
    else:
        print("Please choose 1 or 2.")
print("Pay $" + str(total))
menu loop

A menu that keeps showing until a break runs.

id: menu-loop

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()
if / else

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

What the example draws
Red when x > 0, else blue

id: if-else

for i in range(8):
    if i % 2 == 0:
        pass
    else:
        pass

Example

for i in range(8):
    if i % 2 == 0:
        pencolor("red")
    else:
        pencolor("blue")
    pensize(6)
    forward(30)
    right(45)
every other

i % 2 == 0 is true on every second pass.

What the example draws
Red and blue sides, taking turns

id: every-other

size = 50

Example

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

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

What the example draws
length = 120, then half of it

id: variable

sides = 5
for i in range(sides):
    forward(60)
    right(360 / sides)

Example

sides = 6
for i in range(sides):
    forward(60)
    right(360 / sides)
named turn

Name the number of sides once; the turn is worked out from it.

What the example draws
A hexagon: change sides and the turn follows

id: named-turn

for i in range(20):
    forward(i * 5)
    right(90)

Example

for i in range(30):
    forward(i * 5)
    right(90)
counter step

Use the counter i to make each pass different.

What the example draws
A square spiral: each line longer than the last

id: counter-step

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
grow value

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

What the example draws
The same spiral, grown by an update

id: grow-value

colours = ["red", "blue", "green"]
list

Keep many values in order under one name. The first item is place 0.

id: list

for c in colours:
    pass

Example

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

Work through a list, one item at a time.

What the example draws
One line per colour in the list

id: for-each-item

def shape():
    pass

shape()

Example

def zigzag():
    left(45)
    forward(30)
    right(90)
    forward(30)
    left(45)

zigzag()
zigzag()
zigzag()
def (function)

Name a group of steps, then run it by calling its name.

What the example draws
Defined once, called three times

id: def-function

print("Hello")
print

Show text or a value in the output box.

id: print

import random

n = random.randint(1, 10)
random number

Pick a random whole number between two values.

id: random-number

Text and collections

command = command.strip().lower()
strip and lower

strip() removes spaces at the ends; lower() and upper() change the capitals. Each gives back new text.

id: strip-and-lower

words = command.split()
split

Cut text into a list of words at the spaces: "go north".split() is ["go", "north"].

id: split

if item in bag:
    pass
in

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

id: in

", ".join(bag)
join

Join a list of texts into one, with the text in quotes between each: "lamp, key".

id: join

bag.remove("lamp")
remove from a list

Take an item out of a list. It stops with a ValueError if the item is not there, so check with in first.

id: remove-from-a-list

items.sort()
sort

Put a list in order (A to Z, or smallest first). It changes the list itself.

id: sort

try:
    n = int(text)
except ValueError:
    print("That is not a number.")
try and except

Run lines that might fail. If the named error happens, the except lines run instead of the program stopping.

id: try-and-except

Data

import csv

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

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

id: read-a-csv

counts = {}
for row in rows:
    key = row["genre"]
    if key in counts:
        counts[key] = counts[key] + 1
    else:
        counts[key] = 1
count with a dictionary

One count for each different value: add 1 if the key is there already, or start it at 1.

id: count-with-a-dictionary

print(label.ljust(12) + "#" * n)
a text bar

"#" * 5 is #####. ljust pads the label to the same width, so the bars line up.

id: a-text-bar

assert clean_hours("5") == 5
test with assert

A test case: nothing happens if it is true; the program stops with AssertionError if it is not.

id: test-with-assert

import pandas as pd

songs = pd.read_csv("music.csv")
read a CSV with pandas

Reads the whole file into a table (a DataFrame). Numbers stay numbers.

id: read-a-csv-with-pandas

rows = songs[songs["genre"] == genre]
filter a table

Keeps the rows where the test is true, as a smaller table.

id: filter-a-table

import gradio as gr

def answer(choice):
    return "You chose " + choice

gr.Interface(fn=answer, inputs=gr.Dropdown(["pop", "rock"]), outputs="text").launch()
an app with Gradio

Gradio calls your function with what was chosen, and shows what it returns.

id: an-app-with-gradio

{"q": "What is 7 x 8?", "choices": ["54", "56", "64"], "answer": "56"}

inputs.append(gr.Radio(q["choices"], label=q["q"]))
a quiz question

A question as a dictionary, and a Radio input made from it: the student picks one of the choices, and the function gets that text.

id: a-quiz-question

import requests

try:
    reply = requests.get("https://api.open-meteo.com/v1/forecast", params={"latitude": -35.28, "longitude": 149.13, "daily": "temperature_2m_max"}, timeout=10).json()
except requests.RequestException:
    print("No connection")
ask an API

Asks an API at that address (params become the ?query string) and turns the JSON reply into dictionaries and lists. Plan for no connection.

id: ask-an-api