if, elif, else

The full decision shape

Everything you have written so far runs the same lines on every run. Real programs earn their keep by deciding: is this password correct, does this order qualify for free shipping, which band does this score fall in. The if statement is how a program takes different paths for different data, and it appears in essentially every function you will ever read.

An if statement runs its indented block only when its condition is True. The complete shape has three parts:

score = 83
if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
else:
    print("F")

elif means else if: checked only when everything above it was False. else catches whatever is left. Python tests the conditions top to bottom and runs exactly one branch, then jumps past the whole chain. That is why score >= 80 is safe as the second test: reaching it already proves the score is below 90.

Comparisons: == equal (two signs, = alone is assignment), != not equal, <, >, <=, >=. Indentation is not decoration in Python, the 4 spaces are how it knows what belongs to each branch.