File "bmi.py", line 1, in <module>
    while true:
NameError: name 'true' is not defined

while true:
    height=input("身長(m)?:")
    if len(height)==0:
        break
    height=float(height)
    weight=float(input("体重(kg)?:"))
    bmi=weight/pow(height,2)
    print("BMI値は{:.1f}です。".format(bmi))
    if bmi<18.5:
        print("Mr.ガリガリ君")
    elif 18.5<=bmi<25.0:
        print("中肉中背THEふつう君")
    elif 25.0<=bmi<30.0:
        print("デブ")
    else:
        print("末期のデブ")