workshop_2.md

Workshop 2 — Input, Strings, and Booleans

Prerequisites

• Workshop 1: variables, data types, type casting, f-strings, operators

1. Getting input from the user

So far every value in our programs was written directly in the code. input(...) lets the user type a value while the program runs:

name = input("What is your name?\n")
print(f"Hello, {name}!")

The text inside the parentheses is the prompt — it's printed first, then the program waits until the user presses Enter. Whatever they typed is returned and stored in name.

The prompt can be in any language:

city = input("სად ცხოვრობ?\n")

2. input() always returns a str

Even if the user types 42, input() gives you back the text "42", not the number 42:

age = input("How old are you?\n")
print(type(age))    # <class 'str'>
print(age + 1)      # TypeError: can only concatenate str (not "int") to str

3. Casting input

To do math with what the user typed, cast it — exactly like in Workshop 1:

age = int(input("How old are you?\n"))
print(f"In 5 years you will be {age + 5}.")

Use float(...) instead when the value can have a decimal point (a price, a temperature, a height).

If the user types something that isn't a number ("twenty"), int(...) raises a ValueError. We'll learn how to handle that later — for now, type valid numbers when testing.

4. Strings and escape sequences

A string can use single or double quotes — both mean the same thing:

first = 'Ada'
last = "Lovelace"

Inside a string, a backslash \ starts an escape sequence — a special character you can't easily type directly:

Sequence	Meaning
\n	new line
\t	tab
\"	a double quote inside a "..." string
\\	a single backslash

print("Name:\tAda\nAge:\t25")
# Name:   Ada
# Age:    25

5. String methods

A method is a function that belongs to a value. You call it with a dot after the value. Strings come with many useful methods:

text = "   hello World   "

print(text.upper())    # "   HELLO WORLD   "
print(text.lower())    # "   hello world   "
print(text.strip())    # "hello World"  (spaces removed from both ends)
print(text.strip().title())  # "Hello World"

Methods don't change the original string — they return a new one. To keep the result, assign it:

name = input("Name: ").strip()

len(...) tells you how many characters a string has:

print(len("Ada"))   # 3

6. Booleans

Every comparison produces a bool — either True or False:

age = 20
is_adult = age >= 18
print(is_adult)          # True
print(type(is_adult))    # <class 'bool'>

A handy f-string trick: put = after an expression and Python prints both the expression and its value:

x = 10
print(f"{x > 5 = }")     # x > 5 = True

7. Truthiness

bool(...) converts any value to True or False. The rule is simple: empty or zero is False, everything else is True.

print(bool(0))        # False
print(bool(-5))       # True
print(bool(""))       # False  (empty string)
print(bool(" "))      # True   (a space is not empty!)
print(bool("0"))      # True   (a non-empty string, even if it says 0)
print(bool("False"))  # True   (same reason)

8. Floats aren't exact

Computers store decimal numbers in binary, so some values can't be represented exactly:

print(0.1 + 0.2)          # 0.30000000000000004
print(0.1 + 0.2 == 0.3)   # False

Use round(value, digits) to round to a fixed number of decimal places:

print(round(0.1 + 0.2, 2))   # 0.3
print(round(3.14159, 2))     # 3.14

9. Constants

A constant is a variable that should never change after it's set. Python doesn't enforce this — it's a naming convention: write the name in ALL_CAPS to tell other programmers "don't reassign this".

VAT_RATE = 0.18
price = 100
print(f"With VAT: {price * (1 + VAT_RATE)}")

What's next

See workshop_2/ for runnable examples, and your homework in python-127-homework-2.