1. lambda--- for the function never use again --single line function with no name

square= lambda num:num *num #lambda is automatically returned

print(square(7)) #49

add = lambda a,b :a+b

print(add(2,9))

def square2(num) : return num * num

print(square2(8)) #64

print(square2.__name__) # square2

print(square.__name__) #<lambda> ---lambda function don't have name

print(add.__name__) #<lambda>

#example

import tkinter as tk

# DON'T WORRY ABOUT ANY OF THIS CODE

root = tk.Tk()#=====================

frame = tk.Frame(root)#=============

frame.pack()#=======================

# DON'T WORRY ABOUT ANY OF THIS CODE

# Don't need this function if we use a lambda

# def say_hi():

# print("HELLO!")

button = tk.Button(frame,

text="CLICK ME",

fg="red",

command=lambda: print("Hello"))

button2 = tk.Button(frame,

text="CLICK ME",

fg="red",

command=lambda: print("Bye"))

# DON'T WORRY ABOUT ANY OF THIS CODE

button.pack(side=tk.LEFT) #=========

root.mainloop() #===================

# DON'T WORRY ABOUT ANY OF THIS CODE

3.map

# a standard function that accepts at least two arguments: a funtion and a iterable(list, strings, set, dictionary...)

#runs the lambda for each value in the iterable and returns a map object which can be converted into another data structure

nums = [1,2,5,7,9]

doubles = map(lambda x : x *2, nums)

#map can be converted only once--#<map object at 0x104bc9e48>

res = list(doubles)

print(res) #[2, 4, 10, 14, 18]

4.filter

#There is a lambda for each value in the iterable

#returns filter object which can be converted into other iterables

#The object contains only the values that return true to the lambda

lis = [1, 2, 3, 4]

evens = list(filter(lambda x: x-1 ==3, lis)) #第二个参数是要循环的变量集

print(evens) #[4]

names = ["austin", "penny", "angel", "billy"]

a_names = filter(lambda n : n[0] == 'a', names)

print(type(a_names)) #<class 'filter'>

print(list(a_names)) #['austin', 'angel']

print(list(a_names)) #[] --#转化完只有效一次

names2 = ["Lalali", "Colt", "Rusty"]

print(list(map(lambda name : f"Your instructor is {name}", filter(lambda value: len(value) < 5,names2))))

#['Your instructor is Colt']