Dr Python

Use input() to read text. Python calls a piece of text a string.

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

Try it: Type Alex. The console shows: Hello Alex

Remember: input() gives you a string, even if you type digits.

Put int() around input() to turn the answer into a whole number.

age = int(input("How old are you? "))
print("Next year you will be", age + 1)

Try it: Type 13. The console shows: Next year you will be 14

Remember: Enter a whole number such as 13. Words or decimal numbers will cause an error.

Read two numbers, add them with +, then show the total.

first = int(input("First number: "))
second = int(input("Second number: "))
total = first + second
print("Total:", total)

Try it: Type 7, then 5. The console shows: Total: 12

Remember: Convert both answers with int(). Otherwise, Python joins the text: "7" + "5" becomes "75".

Use print() to show a message in the console.

print("Hello, world!")

Try it: The console shows: Hello, world!

Remember: Put quotation marks around text. Do not put them around variable names.

A variable is a name for a value. Use = to store a value under that name.

score = 10
score = score + 5
print(score)

Try it: The console shows: 15

Remember: Read the right side of = first. Then store the result in the name on the left.

Use float() when an answer can have a decimal point.

price = float(input("Price: "))
print("Double the price:", price * 2)

Try it: Type 2.5. The console shows: Double the price: 5.0

Remember: int() is for whole numbers. float() can read numbers such as 2.5.

Use if to check a condition. Use else for what to do when it is false.

age = int(input("Age: "))
if age >= 12:
    print("You are 12 or older")
else:
    print("You are under 12")

Try it: Type 13. The console shows: You are 12 or older

Remember: End if and else lines with a colon. Indent the code underneath by four spaces.

Use a for loop to repeat code. range(3) gives the values 0, 1 and 2.

for number in range(3):
    print("Hello", number)

Try it: The console shows Hello 0, Hello 1 and Hello 2 on separate lines.

Remember: range(3) stops before 3. The indented line runs three times.

A while loop keeps going while its condition is true.

count = 1
while count <= 3:
    print(count)
    count = count + 1

Try it: The console shows 1, 2 and 3 on separate lines.

Remember: Change count inside the loop. Without that change, this loop would never finish.