Variables and Data Types

Variables

A variable is a name that stores a value, so you can use it later. Create one with =:

Ifeoma
20

Read = as "is set to", not "equals": age = 20 means "set age to 20". The name goes on the left, the value on the right.

Once a variable exists, use its name anywhere you'd use the value:

10000

Changing a variable

A variable holds one value at a time. Assign again and the old value is replaced:

5000
3200

You can use a variable's current value to work out its new one. This is very common:

3200

Python works out the right-hand side first (5000 − 1800), then stores the answer in balance. There's a shortcut for it, balance -= 1800, and the same for the other operators: +=, *=, /=.

Naming variables

And by convention:

• use lowercase with underscores (monthly_budget), called snake_case;
• choose names that say what's inside: transport_cost beats x or tc.

Several at once

You can assign several variables in one line, matching names to values in order:

Ibadan Oyo

Data types

Every value has a type, which decides what you can do with it. You can add two numbers, but you can't sensibly multiply two names. Python's main types:

Check any value's type with type():

<class 'str'>
<class 'int'>
<class 'float'>
<class 'bool'>
<class 'NoneType'>

Strings

Text goes in quotes, single or double; both work, as long as they match. Use double quotes when the text contains an apostrophe:

Economics
I'm in 200 level

Numbers: int and float

A number with a decimal point is a float, even if it ends in .0:

<class 'int'>
<class 'float'>

Don't use commas inside numbers: 60,000 isn't sixty thousand to Python. Write 60000, or use an underscore to make it readable: 60_000.

60000

Booleans

True and False (capital first letter, no quotes) are answers to yes/no questions. You'll get them from comparisons:

True
False

You'll use booleans all the time in the lesson on conditions.

None

None means "no value". It's what you store when a value isn't known yet:

None

Converting between types

Values often arrive as the wrong type, especially numbers stored as text (from a form, a file or a spreadsheet). Text that looks like a number doesn't behave like one:

55
10

With text, + joins; with numbers, it adds. Convert with these functions:

50000
9
7.0
2026 budget

Note that int(9.99) gives 9: it cuts off the decimals, it doesn't round. Use round(9.99) to round.

Conversions only work when they make sense:

int("forty")

ValueError: invalid literal for int() with base 10: 'forty'

A ValueError means the value can't be converted.

Putting values into text

To mix text and numbers in one message, use an f-string: put f before the opening quote, and variables inside {curly brackets}:

Musa is in 300 level

Without an f-string, joining text and a number with + fails, because they're different types:

print("Level: " + level)

TypeError: can only concatenate str (not "int") to str

Fix it with an f-string, f"Level: {level}", or by converting, "Level: " + str(level). You'll learn much more about f-strings in the lesson on text.

Getting input from the user

input() pauses your program and waits for someone to type, then gives you what they typed, always as text:

name = input("What is your name? ")
age = int(input("How old are you? "))
print(f"Hello {name}, next year you'll be {age + 1}")

Notice int(...) around the second input: without it, age would be text and age + 1 would fail. In Colab, a box appears under the cell for you to type into.

Summary

Try it