Lesson 3 of 8 · 32 min · Grades 6–8
Variables — labelled bags
In a school bag, the pencil box is labelled so it is not mixed with tiffin. A variable is a labelled bag in the computer’s memory: the name stays on the outside, the contents can change. When Asha says pencils = 8 she is not writing poetry — she is putting the number 8 into a bag named pencils.
Labelled school bag
Variables are named pockets.
You will be able to
- ✓ Create variables with =
- ✓ Store numbers and text in named bags
- ✓ Print a variable and use it in a later line
Assignment is putting something in a bag
The symbol = in Python is not the “equals” of a maths identity. It is an action: evaluate the right-hand side, store that result in the name on the left. pencils = 8 means “bag pencils now holds 8”.
Later, pencils = 7 replaces the contents. The old 8 is gone. There is no history unless you saved it in another variable. That is why we name carefully — you will look for this bag again.
Names you (and Python) can read
Use lowercase words that say what is inside: total, marks, city, bus_fare. Do not start with a number. Do not use spaces. An underscore joins words: house_points.
Python is case-sensitive: Marks and marks are different bags. Stick to lowercase so you never wonder which one you meant. Avoid names like list or print — those already mean something to Python.
Two kinds of contents you will use today
Integers are whole numbers: 8 pencils, 40 rupees, class 7. Strings are text: "Asha", "Blue". Mixing them in print is fine: print("Pencils", pencils). Mixing them with + is not: "Asha" + 8 is a type error in real Python.
When you are unsure what a bag holds, print it. The console is your X-ray. Professional programmers still do this — they just call it logging.
Words that matter
- Variable
- A named place in memory that holds a value.
- Assignment
- The = action that stores a value in a name.
- Integer
- A whole number, like 12 or 0.
Common mistakes
Avoid: Thinking = asks a question (is it equal?).
Do this: Use = to store. Use == later, in if, to compare.
Avoid: Naming a variable x1, tmp2, data3 with no meaning.
Do this: Name after the real thing: erasers, bus_fare, house.
Example program — Asha's school bag
Change the numbers and Run again. The printed totals follow the bags, not the old story in your head.
Edit the example, press Run, then Build if you want a compile check.
build
Press Build to compile.
Your turn — Count your kit
Store notebooks as 4 and pens as 3. Print a line that includes the total 7.
Edit the example, press Run, then Build if you want a compile check.
build
Press Build to compile.
Self-assessment
Check your understanding before you mark the lesson complete.
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