Python学习笔记（5）：函数

在前面我们已经见过一些Python内建函数，比如len和rang。现在我们来看看自定义函数，函数是通过def关键字来定义，后面跟函数名称和圆括号，括号内可以包含参数，该行以冒号结束，接下来是语句块，即函数体。

1. 简单的sayHello函数

def sayHello():

    print("Hello world!")



#调用函数

sayHello()

2. 带形参函数

def printMax(a, b):

    if a > b:

        print(a, "is maximum.")

    else:

        print(b, "is maximum.")



printMax(3, 4)

3. 局部变量

def func(x):

    print("x is ", x)

    x = 2

    print("Changed local x to ", x)



x = 50

func(x)

print("x is still ", x)

运行结果为：

x is  50
Changed local x to  2
x is still  50

4. 默认参数值

def say(message, times = 1):

    print(message * times)



say("ha")

say("ha", 2)

运行结果为：

ha

haha

5. 关键参数

def func(a, b = 5, c = 10):

    print("a is", a, "and b is", b, "and c is", c)



func(3, 7)

func(25, c = 24)

func(c = 50, a = 100)

运行结果为：

a is 3 and b is 7 and c is 10
a is 25 and b is 5 and c is 24
a is 100 and b is 5 and c is 50

6. return语句

def maximum(x, y):

    if x > y:

        return x

    else:

        return y



print(maximum(2, 3))

7. 文档字符串DocStrings

Python有一个奇妙的特性，就是文档字符串（DocStrings），它的主要作用就是帮助你的程序文档更加简单易懂。

def printMax(x, y):

    '''Prints the maximum of two numbers.

    The two values must be integers.'''

    x = int(x)

    y = int(y)



    if x > y:

        print(x, "is maximum.")

    else:

        print(y, "is maximum.")



printMax(3, 5)

print(printMax.__doc__)

help(printMax)

运行结果为：

5 is maximum.
Prints the maximum of two numbers.
    The two values must be integers.
Help on function printMax in module __main__:

printMax(x, y)
    Prints the maximum of two numbers.
    The two values must be integers.