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Function

Function函數​

  • 撰寫一次之後可不斷重複使用的程式碼
  • 更好管理及維護
def mytest():                       //can have no argument
    print('hi')
def myFunction(name):               //can have argument
    print('hello'+name)
myFunction('john')

def requiredArg(name, grade):       //can have more than 1 argument
    print(name + ' math grade is ' + %grade)
requiredArg('peter',78)

def defaultArg(name, msg='morning')://can have default arguments
    print(name + msg)
defaultArg('celine')

def variousArg(*meals):             //can be 1 or more arguments
    for meal in meals:
        print(meal)
variousArg('pasta','steak','burger')

def lunch(**mydict):                //can accept dictionary as argument
    print('your lunch include: ',mydict)
dinner('entree':'steak','drink':'wine','desert':'tiramisu')

函數回傳值​

  • 函數可以設定回傳值(return)
  • 回傳值可以是一個或多個
def returnMe():
    a='hi'
    b='you'
    return a,b
returnMe()

__main__主程式​

  • 當 Python 檔案（模組、module）被引用的時候，檔案內的每一行都會被 Python 直譯器讀取並執行
  • 若要在被引用時，不該執行的程式碼不被執行？當然就是靠 name == 'main'做判斷
def main():
    print('main function here!')
def printHello():
    print('Hello Here!')
if __name__ == "__main__":        //if this is the main thread, execute this function 
    main()

Builtin Function 內建函數​

  • Python程式語言內建不少函數
abs(-1)     //get the absolute value
round(3.4)  //round to nearest whole number
pow(3,2)    //get 3*3 = 9
divmod(5,2) //返回商數和餘數 (2,1)
list=[1,2,3,4,5]
sum(list)   //加總list的內容 = 15
min(list)   //取得最小值
max(list)   //取得最大值

Global and local 全域變數與區域變數​

  • 全域變數：任何區塊的程式碼都可存取的變數
  • 區域變數：只有在程式區塊內才可存取的變數
c=99
def sum(a,b):
    global c    //需要宣告要用到全域變數
    sum = a+b+c
    return sum
print(sum(1,2))

Lambda 匿名函數​

  • 可以使用一行就完成的函數定義
  • 更精簡的函數寫法
x = lambda a : a*2
print(x(5))

filter函數​

  • 可篩選出符合條件的元素
mylist = [1,2,3,4,5,6,7,8,9,10]
oddonly = list(filter(lambda x: (x%2==1), mylist))      //只挑出奇數（odd）指不能被2整除的整數
print(oddonly)

map函數​

  • Map函數：可以將每個元素做轉換
mylist = [1,2,3,4,5,6,7,8,9,10]
sqrtlist = list(map(lambda x: x**2, mylist))      //將list的每個元素都做平方,然後顯示出來
print(sqrtlist)

reduce函數​

  • Reduce函數：可以將多個元素拆解做合併
from functools import reduce        //需要引reduce入工具
mylist = [1,2,3,4,5]
reduced = reduce(lambda x,y : x+y, mylist)  //將每兩個元素加總後變成第一個元素,在跟後面一個元素加總
// (((((1+2)+3)+4)+5) = 15