023. Comparison Operators

RAM Manager — Alert Severity Levels

Aryan’s RAM manager needs to classify current memory pressure into severity levels so the dashboard can color-code alerts:

Usage %	Level
< 50%	“normal”
50–74%	“warning”
75–89%	“critical”
>= 90%	“emergency”

He writes classify_usage(used_pct), but the boundary between “warning” and “critical” is wrong — his code uses < 70 where it should be < 75. So a process at 72% usage is incorrectly classified as “critical” instead of “warning”, firing unnecessary pages.

The lesson: Off-by-a-few comparisons are silent bugs. The code runs, returns a value, and looks plausible — but the boundary is in the wrong place. Always verify the exact threshold values against the spec.

💡 Fun fact: Python supports chained comparisons natively: 0 <= x < 10 is valid Python and evaluates correctly without parentheses. In C, you would need x >= 0 && x < 10. Python’s chaining mirrors standard mathematical notation and is unique among mainstream programming languages.

⚠️ Watch out: The single most common comparison mistake is using = (assignment) instead of == (equality check) inside an if condition. In C this produces a silent logic error; Python raises a SyntaxError for if x = 5:, which saves you from this particular trap — but wrong boundary values (like < 10 instead of < 15) are completely silent.

🤔 Think about it: Once an `if celsius < 0` check passes, you know `celsius` is negative in the else branch. How does Python’s `elif` cascade let you simplify subsequent conditions, and why does removing redundant checks make code easier to read?

Learning objectives

Use ==, !=, <, >, <=, >= for comparisons
[object Object]
Simplify elif conditions by relying on prior checks

Key concepts

comparison operators
==
<
=

Try it

Concept detail

Python comparison operators return boolean values (True/False): == (equal), != (not equal), < (less), > (greater), <= (less or equal), >= (greater or equal). Python allows chaining: 0 <= x < 10 is the same as (0 <= x) and (x < 10). Common mistake: using = (assignment) when == (comparison) is needed. After an if checks one condition, subsequent elif/else runs only when previous conditions were False, so you don’t need to re-check. This simplifies conditions.

Solution

def classify_temp(celsius):
    if celsius < 0:
        return "freezing"
    elif celsius < 15:
        return "cold"
    elif celsius < 25:
        return "comfortable"
    else:
        return "hot"

Tests

def test_freezing():
    assert classify_temp(-5) == "freezing"
    assert classify_temp(-0.1) == "freezing"

def test_cold():
    assert classify_temp(0) == "cold"
    assert classify_temp(10) == "cold"
    assert classify_temp(14) == "cold"

def test_comfortable():
    assert classify_temp(15) == "comfortable"
    assert classify_temp(20) == "comfortable"
    assert classify_temp(24) == "comfortable"

def test_hot():
    assert classify_temp(25) == "hot"
    assert classify_temp(40) == "hot"