Function & Class
Python - Lesson 4
講師：溫室蔡
什麼是函式
什麼是函式
f (x) = 2x + 3
f (3) = 9
f (7) = 17
Python 中的函式
def f(x): return 2*x + 3 print(f(3)) # 9 print(f(7)) # 17
函式語法
def 函數名稱(參數1, 參數2, ...): # 你要做的事情 # ... # ... return 回傳值
P.S. "def" 是 "define"（定義）的意思
函式不一定要回傳值
def greet(name): s = 'Hello, ' + name + '!' print(s) greet('John') # Hello, John! greet('Mike') # Hello, Mike!
變數作用範圍
def greet(name): s = 'Hello, ' + name + '!' print(s) greet('John') # Hello, John! greet('Mike') # Hello, Mike! print(s) # NameError: name 's' is not defined
在函式內定義的變數
只作用於函式範圍內
遞迴（recursion）
def fact(n): if n == 1: return 1 return n * fact(n-1)
在函式當中呼叫自己
遞迴範例：階乘
def fact(n): if n == 1: return 1 return n * fact(n-1)
1! = 1
n! = n (n – 1)!
4! = 4×3×2×1
= 4×3!
遞迴範例：費氏數列
a1 = 1
a2 = 1
an = an–1 + an–2
1, 1, 2, 3, 5, 8, 13, 21, 34, ...
遞迴範例：費氏數列
a1 = 1
a2 = 1
an = an–1 + an–2
def fib(n): if n == 1 or n == 2: return 1 return fib(n-1) + fib(n-2)
Python 函式小技巧
回傳多個值
def max_min(n): a = max(n) b = min(n) return a, b n = [8, 4, 3, 7, 1] x, y = max_min(n) print(x) # 8 print(y) # 1
參數預設值
def greet(name, time='morning'): print(f'Good {time}, {name}!') greet('John') # Good morning, John! greet('John', 'evening') # Good evening, John! greet('John', 'night') # Good night, John!
不定數目參數
def double(*a): for i in a: print(i*2) double(3) # 6 double(2, 3, 4) # 4 # 6 # 8
把函式當參數
def vfunc(a, f): n = [] for i in a: n.append(f(i)) return n def plus_one(x): return x+1 def square(x): return x*x x = [1, 2, 3] print(vfunc(x, plus_one)) # [2, 3, 4] print(vfunc(x, square)) # [1, 4, 9]
Class（類別）
定義一個物件（object）
每個物件會有自己的變數
稱為屬性（attribute）
以及自己的函式
稱為方法（method）
例：人有名字（屬性，字串）
體重（屬性，數字）
會吃東西（方法）
寫一個 Class
class Person: def __init__(self, name, height, weight, money): self.name = name self.height = height self.weight = weight self.bmi = weight / (height/100)**2 self.money = money p = Person('Justin', 170, 60, 1000) print(p.name) # Justin print(p.height) # 170 print(p.weight) # 60 print(p.bmi) # 20.76 print(p.money) # 1000
Class 語法
class 類別名稱: def __init__(self, 參數1, 參數2, ...): self.屬性1 = 值1 self.屬性2 = 值2 # ... # 其他一開始要做的事 變數 = 類別名稱(參數1, 參數2, ...)
__init__() 是 initialization 的意思
也就是「初始化」
在物件被建立的時候
先做一些設定之類的事
Class 範例：Food
class Food: def __init__(self, name, price, kcal): self.name = name self.price = price self.kcal = kcal foods = [] foods.append(Food('apple', 50, 70)) foods.append(Food('banana', 30, 100)) foods.append(Food('orange', 40, 50)) print(foods[0].name) # apple print(foods[1].price) # 30 print(foods[2].kcal) # 50
寫一個方法
class Person: def __init__(self, name, height, weight, money): self.name = name # 以下略 def eat(self, food): if self.money < food.price: print('Too expensive') return self.money -= food.price self.weight += food.kcal / 100 print(f'{name} ate a {food.name}!') p = Person('Justin', 170, 60, 1000) f = Food('apple', 50, 70) p.eat(f) # Justin ate a apple! print(p.money) # 950 print(p.weight) # 60.7
寫一個方法
class Person: # ... # ... p.eat(f) print(p.weight) # 60.7 (增加了) print(p.bmi) # 20.7 (沒跟著改)
self.bmi 與 self.weight 連動
self.eat() 改了 self.weight
但沒改到 self.bmi
成員權限
其中 private 成員只能被自己內部存取
前面加兩條下劃線可讓成員變成 private
class Example: def __init__(self): self.x = 10 # public self.__y = 20 # private a = Example() print(a.x) # 10 print(a.y) # AttributeError print(a.__y) # AttributeError
class 的成員分成 public 跟 private
成員權限
class Example: def __init__(self): self.x = 10 # public self.__y = 20 # private def y(): # Getter return self.__y def set_y(value): # Setter self.__y = value a = Example() print(a.y()) # 20 a.set_y(37) print(a.y()) # 37
如果要存取 private 成員
就要寫 getter 跟 setter
分別用來取值與賦值
成員權限
class Person: def __init__(self, name, height, weight, money): # ... self.__weight = weight # ... def weight(): # Getter return self.__weight def set_weight(weight): # Setter self.__weight = weight self.bmi = weight / (self.height/100)**2 def eat(self, food): # ... self.set_weight(self.weight() + food.kcal / 100) # ... # ... p.eat(f) # Justin ate a apple! print(p.weight) # AttributeError: type object 'Person' has no attribute 'weight' print(p.__weight) # AttributeError: type object 'Person' has no attribute '__weight' print(p.weight()) # 60.7 print(p.bmi) # 21.0
繼承（inheritance）
若 B 繼承了 A
則 B 會有 A 的
所有屬性與方法
同時還能
再為 B 定義
專屬的成員
class A: def __init__(self, x, y): self.x = x self.y = y def do_a(self): print('I can do A') class B(A): def __init__(self, x, y, z): super().__init__(x, y) self.z = z def do_b(self): print('It is possible for me to do B') p = A(1, 2) q = B(3, 4, 5) print(p.x) # 1 print(q.x) # 3 print(q.z) # 5 p.do_a() # I can do A q.do_a() # I can do A q.do_b() # It is possible for me to do B
繼承語法
class 類別名稱B(被繼承的類別A): def __init__(self, A的參數, B自己的參數): super().__init__(A的參數) # 跑一遍 A 的 __init__() self.B自己的參數1 = 值1 # 自己的參數自己 init self.B自己的參數2 = 值2 # ... # 自己的方法自己寫 def B自己的方法1(self, 參數1, 參數2, ...): # ... def B自己的方法2(self, 參數1, 參數2, ...): # ... #...
繼承範例：Student
class Person: # ... class Student(Person): def __init__(self, name, height, weight, money, iq): super().__init__(name, height, weight, money) self.iq = iq self.grades = {} def study(self, hours): self.iq += hours / 10 def take_test(self, subject, luck): score = int(iq/150 * 100 * luck) self.grades[subject] = score if (score > 80): money += 100 s = Student('Justin', 170, 60, 300, 120) s.eat(Food('apple', 50, 70)) # Justin ate a apple! s.study(2) print(s.iq) # 120.2 s.take_test('math', 0.9) print(s.grades['math']) # 72
謝幕
講到這邊也夠了
如果想學更多物件導向的話
歡迎來上星期三的專案建置小社
Function & Class Python - Lesson 4 講師：溫室蔡
pyclass
By Justin Tsai
pyclass
- 360
