Lambda expression is also known as an anonymous function, which means that we don't give a function name.

We use lambda functions when we require a nameless function for a short period of time. In Python, we generally use it as an argument for a higher-order function. Lambda functions are used along with built-in functions like filter() , map() etc.

The value computed by lambda expression will be returned automatically.

• It’s named after lambda calculus, which is way outside the scope of this course. For your information, Lambda calculus is Turing complete; that is, it is a universal model of computation that can be used to simulate any Turing machine.

# lambda expression

result = (lambda x: x**2)(5)  # 匿名function 自帶return 效果/可輸入input

print(result)

# lambda expression多變數輸入

result_2 = (lambda x, y: (x+y, x-y))(x=5, y=6)

print(result_2)

--------------------------------------------------------------------

25
(11, -1)

# higher order function by map / filter function

for item in map(lambda x: x**2, [5, 10, 15, 20]): # 做原function 的疊加 ，次方 + list input 
    print(item)

for item in filter(lambda x: x % 2 == 0, [5, 10, 15, 20]): # 做判斷值是否為偶數
    print(item)

--------------------------------
#map 
25
100
225
400

#filter return 

10
20

refer from below

• Lambda函式，也就是匿名函式，不需要定義名稱，只有一行運算式，語法非常簡潔，功能強大，所以現代程式語言如Java、C#及Python等都支援Lambda函式，適用於小型的運算，Python的一些內建函式甚至使用它作為參數值的運算。

• lambda關鍵字

• parameter_list(參數清單)

• expression(運算式)

[Python教學]Python Lambda Function應用技巧分享