BMI Category

体重指数分类

≈ 15 min · python-conditionals · Open in WolfCode

Same elif chain — but now the technique is monotonic ordering: by going low-to-high, each branch's condition becomes a single upper bound. No and needed.

The thresholds

bmi < 18.5 → "Underweight"
18.5 <= bmi < 25 → "Normal"
25 <= bmi < 30 → "Overweight"
bmi >= 30 → "Obese"

The cleanest pattern

Python · runnable

def bmi_category(bmi):
    if bmi < 18.5:
        return "Underweight"
    elif bmi < 25:
        return "Normal"
    elif bmi < 30:
        return "Overweight"
    else:
        return "Obese"

for value in [17.0, 22.0, 27.5, 31.0, 18.5, 25.0, 30.0]:
    print(f"bmi_category({value:>5}) = {bmi_category(value)}")

Loading Python runtime (~5 MB, one-time)…

Verbose alternative (also correct)

Defensive — survives someone reordering branches

def bmi_category(bmi):
    if bmi < 18.5:
        return "Underweight"
    elif 18.5 <= bmi < 25:
        return "Normal"
    elif 25 <= bmi < 30:
        return "Overweight"
    elif bmi >= 30:
        return "Obese"

print(bmi_category(22))
print(bmi_category(18.5))
print(bmi_category(25))

Loading Python runtime (~5 MB, one-time)…

Check yourself

What does bmi_category(25.0) return with the LOW-TO-HIGH version?

Now you try

Open 02-bmi-category.py. Implement the function — the autograder runs 7 tests covering each category plus the three boundary values.