Good question — and the fact that you're asking it after a week of writing code means your instincts are developing. Last week you used variables as tools. This week you'll understand them as concepts.

Python does two things when you write x = 5. First, it creates the value 5 in memory. Second, it attaches the name x to that value — like sticking a label on a box. The = sign is the assignment operator. It doesn't mean "equals" in the math sense. It means "make this name point to this value."

x = 5
y = x + 3
print(y)  # 8

The right side is evaluated first. Python computes x + 3 (which is 8), then assigns the result to y.

An expression is anything Python can evaluate to produce a value. Numbers, strings, math operations, function calls, comparisons — all expressions.

42              # literal expression
x + 3           # arithmetic expression
len("hello")    # function call expression
x > 10          # comparison expression (produces True or False)

A statement, on the other hand, is an instruction that does something. Assignments, if blocks, for loops — those are statements. The key difference: expressions produce values, statements perform actions.

# Statement: assigns a value
total = 10 + 20

# Expression: the 10 + 20 part produces 30
# Statement: the total = ... part stores it

Remember how last week you wrote if score >= 90:? The score >= 90 part is an expression — it produces True or False. The if ... : part is a statement — it decides what to do next.

That's the classic beginner bug, and you just discovered it yourself — which is great. To check if two things are equal, you use == — the equality operator:

x = 5       # assignment: store 5 in x
x == 5      # comparison: is x equal to 5? → True
x == 10     # comparison: is x equal to 10? → False

If you write if x = 5:, Python throws a SyntaxError because = is assignment, not comparison. Always use == inside conditions. Think of it this way: one = means "store this," two == means "check this."

Variables in Python are even more flexible than cells — you can reassign them anytime:

score = 0
print(score)    # 0

score = score + 10
print(score)    # 10

score += 5      # shorthand for score = score + 5
print(score)    # 15

The += operator is called an augmented assignment. There's also -=, *=, and /=. They all follow the same pattern: take the current value, apply the operation, store the result back. Remember the accumulator pattern from Day 7? That total += score inside the loop? Now you know exactly what it's doing.

Almost anything. Variable names must start with a letter or underscore, can contain letters, numbers, and underscores, and are case-sensitive. But they can't be Python keywords like if, for, def, or return.

my_name = "Alice"    # good
_count = 0           # good (leading underscore is fine)
student2 = "Bob"     # good
2nd_place = "Charlie" # SyntaxError — can't start with a number
for = 10             # SyntaxError — 'for' is a keyword

The convention in Python is snake_case — lowercase words separated by underscores. student_name, not studentName or StudentName.

Now let's practice the difference between assignment and equality.