[Python] - First class functions

1. First class Obejct

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Define

1. You can store them in Variable , Data Structure(list,dictionary .. ) 
2. You can pass the function as a parameter to another function
3. You can return the function from a function.

 

2. First class functions

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Python support first class functions, it means function is instance of Object.

First class functions includes First class Object properties.

 

First class functions's feature

2-1) functions are Object

# 1. Functions are Objects
def change_lower(text):
    return text.lower()

test = change_lower
print(test('HELLO World'))
> hello world

2-2) Functions can be passed as arguements to other functions

# 2. Functions can be passed as arguements to other functions
def change_lower(text):
    return text.lower()

def change_upper(text):
    return text.upper()

def change_word(func,text):
    return func(text)

print( change_word(change_lower,text) )
> hello world
print( change_word(change_upper,text) )
> HELLO WORLD

2-3) Functions can return another functions

how get log object have text?

• log_message function called "closure function"
• closure function remeber local variable after origin function return

# 3. Functions can return another functions
def logging(text):
    def log_message():
        print( 'log_msg : {}'.format(text))

    return log_message

log = logging('test')
print(log)
> <function logging.<locals>.log_message at 0x000001EBFE366EF0>
log()
> log_msg : test

 

Why we use first class function

def logging(risk):
    def wrap_msg(msg):
        print('{0}-{1} '.format(risk,msg))

    return wrap_msg

risk_4 = logging('4')
risk_4('404')
> 4-404
risk_4('400')
4-400

risk_2 = logging(2)
risk_2('200')
> 2-200