Detailed examples of the use of python advanced functions

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Function parameter problem

##Three basic situations

• fun(a,b)

• fun(a,b) b is an iterable object

• fun(a,**b) b is an iteration object with a retrieval type, inside the function body When parsing, it is quite a dictionary

ls = [i for i in range(10)]
#print(ls)
def fun1(a,*b):
    for i in b:
        print(a,i)
#fun1(1,*ls)

def fun2(name,age,**kw):
    print("name:",name,"age:",age,"other:",kw)

fun2('fanhaitao','26',参数= 'random')

**kw参数把键值对转换成字典的形式

Anonymous function

lambda

1. There is no return value, the return value is the value of the expression

2. The function has no name, so don’t worry about name conflicts

3. The anonymous function is also a function object. You can also assign the anonymous function to a variable and use the variable to call the function

fun3 = lambda x:x+1
print(fun3(99))

#100
fun4 = lambda x,y :x*x + y*y
print(fun4(3,4))
#25

Decorator@

This method of dynamically adding functions while the code is running is called "Decorator"

Decorator without parameters

#定义一个装饰器
def log(func):
    def wrapper(*args,**kw):
        print('call %s()' % func.__name__)
        return func(*args,**kw)
    return wrapper
@log
def now():
    print('2018-3-29')
    
now()

The internal logical relationship of the decorator (calling sequence): log() -> return wrapper() -> return func() -> now()

Decorator with parameters

#定义一个装饰器
def log(text):
    def decorator(func):
        def wrapper(*args,**kw):
            print('%s %s():' % (text,func.__name__))
            return func(*args,**kw)
        return wrapper
    return decorator
@log("可爱的参数")
def now():
    print('2018-3-29')

now()

BiF built-in function

zip: Combine two iteration objects into one iteration object

Note: redundant unmatched variables will be discarded

a = [1,2,3]
b = 'abcde'
for i in zip(a,b):
    print(i)
for i,j in zip(a,b):
    print("Index:",i,";Item:",j)

enumerate: returns an iterable object, consisting of position + element

for i,j in enumerate('abcde'):
    print(i,j)

filter: filter Function

Two parameters, the first is a parameter, the second is an iterable object, the returned value is also an iterable object; the iterative object in the parameter is True in the function, The value will be retained, otherwise pass

print(list(filter(lambda x:(x*x+x+2)%8 == 0,range(100))))

map

##The usage is similar to filter, the difference is as follows:

• The function in the parameters operates on each iteration object

• Returns the operated object

  print(list(map(lambda x:x**2,range(5))))

reduce

• In the functools library

• func receives 2 parameters,

reduce continues the result and performs cumulative calculation with the next element of the sequence

from functools import reduce
add = lambda x,y:x+y
ls = [i for i in range(101)]
print(reduce(add,ls))

#5050

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Advanced functions of Python

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##Advanced usage of python functions

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