1、匿名函式是什麼？

def add(x,y):
    return x+y
print(add(1,2))
#普通函式的定義和呼叫

f = lambda x,y:x+y
print(f(1,2))
#匿名函式的定義，並將這個函式賦值給變數，使用變數呼叫函式
print(f(1,2))
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test24.py"
# 3

以上不能體現匿名函式的方便用法。因為一般lambda表示式是不賦值給變數用的。

2、三元表示式

與其他語言不通，python的格式是

為真的結果 if 為真的條件 else 為假的結果

x = 3
y = 2
r = x if x>y else y
print(r)
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test25.py"
# 3

3、map：使用場景--數學上的對映，內部執行了for迴圈，挨著盤用function 算了一下

語法：map(function,interator)

list_x = [1,2,3,4,5,6,7]
def square(x):
    return x*x

r = map(square,list_x)
print(list(r))

# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test26.py"
 

# [1, 4, 9, 16, 25, 36, 49]

總結1～3:map是要結合lambda函式使用的

list_x = [1,2,3,4,5,6,7]

r = map(lambda x:x*x, list_x)
print(list(r))

# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test26.py"
# [1, 4, 9, 16, 25, 36, 49]

簡潔一點。

多個入參

list_x = [1,2,3,4,5,6,7]
list_y = [1,2,3,4,5,6,7]
r = map(lambda
 
 x,y:x*x+y, list_x,list_y)
print(list(r))

# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test26.py"
# [2, 6, 12, 20, 30, 42, 56]

又一個入參比較短，輸出長度按照比較短的那個輸出

list_x = [1,2,3,4,5,6,7]
list_y = [1,2,3,4,5]
r = map(lambda x,y:x*x+y, list_x,list_y)
print(list(r))

# anson@ansonwandeMacBook-Pro python_ToolCodes % python3 test26.py
# [2, 6, 12, 20, 30]

4、reduce

語法def reduce(function, sequence, initial=None)

#連續計算，連續呼叫lambdafrom functools import reduce

list_x = [1,2,3,4,5]
#list_y = [1,2,3,4,5]

r = reduce(lambda x,y: x+y,list_x)
print(r)
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test27.py"
# 15
# 計算過程
# x=1,y=0 y=1--->第一次呼叫lambda

# x=2,y=1 y=3--->第二次呼叫lamda

# x=3,y=3 y=6
# x=4,y=6 y=10
# x=10,y=5 y=15

給個初始值y=10

from functools import reduce
list_x = [1,2,3,4,5]
#list_y = [1,2,3,4,5]

r = reduce(lambda x,y: x+y,list_x,10)
print(r)
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test27.py"
# 25
# 計算過程
# x=1,y=10 y=11
# x=2,y=11 y=13
# x=3,y=13 y=16
# x=4,y=16 y=20
# x=5,y=20 y=25

5、filter：應用場景，過濾為0數字、過濾大寫字母之類的

基礎語法：

過濾為0的數字
list_x = [1,0,1,0]

# def filter_data(x):
#     return x

# for x in list_x:
#     filter_data(x)

r = filter(lambda x:x,list_x)
#r = filter(filter_data,list_x)

print(list(r))
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test28.py"
# [1, 1]