Python 3 -Functions

# computes the area of a triangle
def triangle_area(base, height):     # header - ends in colon，以冒号结尾
    area = (1.0 / 2) * base * height # body - all of body is indented，body必须要退格
    return area                      # body - return outputs value

a1 = triangle_area(3, 8)
print a1
a2 = triangle_area(14, 2)
print a2

# converts fahrenheit to celsius
def fahrenheit2celsius(fahrenheit):
    celsius = (5.0 / 9) * (fahrenheit - 32)
    return celsius

# test!!!
c1 = fahrenheit2celsius(32)
c2 = fahrenheit2celsius(212)
print c1, c2

# converts fahrenheit to kelvin
def fahrenheit2kelvin(fahrenheit):
    celsius = fahrenheit2celsius(fahrenheit)
    kelvin = celsius + 273.15
    return kelvin

# test!!!
k1 = fahrenheit2kelvin(32)
k2 = fahrenheit2kelvin(212)
print k1, k2

# prints hello, world!
def hello():
    print "Hello, world!"

# test!!!
hello()      # call to hello prints "Hello, world!"
h = hello()  # call to hello prints "Hello, world!" a second time
print h      # prints None since there was no return value