Python學習筆記（5）：函數

在前面我們已經見過一些Python內建函數，比如len和rang。現在我們來看看自訂函數，函數是通過def關鍵字來定義，後面跟函數名稱和圓括弧，括弧內可以包含參數，該行以冒號結束，接下來是語句塊，即函數體。

1. 簡單的sayHello函數

def sayHello():    print("Hello world!")#調用函數sayHello()

2. 帶形參函數

def printMax(a, b):    if a > b:        print(a, "is maximum.")    else:        print(b, "is maximum.")printMax(3, 4)

3. 局部變數

def func(x):    print("x is ", x)    x = 2    print("Changed local x to ", x)x = 50func(x)print("x is still ", x)

運行結果為：

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

4. 預設參數值

def say(message, times = 1):    print(message * times)say("ha")say("ha", 2)

運行結果為：

ha

haha

5. 關鍵參數

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)

運行結果為：

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語句

def maximum(x, y):    if x > y:        return x    else:        return yprint(maximum(2, 3))

7. 文檔字串DocStrings

Python有一個奇妙的特性，就是文檔字串（DocStrings），它的主要作用就是協助你的程式文檔更加簡單易懂。

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)

運行結果為：

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.