Built-in Functions and Anonymous Functions

Keywords: Python Lambda encoding ascii

python provides powerful built-in functions, so let's take a look at what these functions do.

Absolute value of abs().

print(abs(-1))
print(abs(0))
Operation result
1
0

abs

all() passes on an iteratable object, each worth bool value of which returns Ture for Ture, one for False, and the result for False.

print(all(i for i in range(10)))#False
print(all(i for i in range(1,10)))#True

all()

sum() converts an object into an iterative object sum.

res=sum(i for i in range(3))
print(res)#3

sum()

any() passes on an iteratable object, in which a bool value of one value is Ture to return Ture, all values are False, and the result is False.

print(any([]))#False
print(any([None,0,'',{},1]))#True

any()

bin() converts the incoming value into binary.

print(bin(3))#0b11

bool() returns the bool value.

print(bool(0))#False
print(bool(None))#False
print(bool(''))#False

bytes() converts a string to byte mode.

print(bytes('hello',encoding='utf-8'))#b'hello'

Whether callable() can be invoked returns the bool value.

def test():
    pass
print(callable(test))#True
print(callable(sum))#True

The corresponding relationship between chr() and ord()ASCII codes.

print(chr(67))#C
print(chr(65))#A
print(ord('A'))#65

Class method, static method, property object-oriented three bitch.

　　classmethod

class people:
    country = 'china'
    # Class method, using classmethod To decorate
    @classmethod
    def getCountry(cls):  #Class methods automatically treat classes as cls Transfer into function
        return cls.country
    @classmethod
    def setCountry(cls, country):
        cls.country = country
p = people()
print(p.getCountry())  # You can use instance object references
print(people.getCountry())  # References can be made through class objects
p.setCountry('japan')
print(p.getCountry())
//Operation results:
china
china
japan

　　staticmethod

class people:
    country = 'china'
    @staticmethod
    # Static methods are bound in a decorator fashion and, like ordinary functions, are not automatically passed on self
    def getCountry():
        return people.country
print(people.getCountry())
//Operation results:
china

　　property

class people:
    __name = 'jeff'
    __age = 12
    def set(self):
        print(self.__name)
        print(self.__age)
p = people()
#print(p.__name,p.__age)   #AttributeError: 'people' object has no attribute '__name'
p.set()
//Operation results;
jeff
12

complex() Complex, defining complex

x=complex(1-2j)
print(x.real)#1.0
print(x.imag)#-2.0
x=1-2j
print(x.real)#1.0
print(x.imag)#-2.0

Data type

int() integer, isinstance() to determine the data type

num=1 #num=int(1)
print(type(num)) #See num Types<class 'int'>
print(isinstance(num,int)) #judge num Whether it is int type True
print(num is 1) #is Identity arithmetic, based on id To judge identity Tr

float() converts numbers into floating-point types.

str() is converted to a string.

list() converts any iterable into a list.

x=list(i for i in range(10))
print(x)#[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

tuple() is converted into tuples.

　　dict()

d={'a':1}
d=dict(x=1,y=2,z=3)
print(d)#{'z': 3, 'x': 1, 'y': 2}

set() is transformed into a set, which is an iterative object and a list.

frozenset() immutable set

s={1,2,3,4,4}
print(s)
s.add(5)
print(s)#set Incremental but immutable sets are not allowed
f=frozenset({1,2,3,4})
print(type(f))

What callable methods are there under the dir() object?

Dimod () returns tuples (x//y, x%y), front-end paging.

print(divmod(100,33))#(3, 1)

enumerate() iterator

for i in enumerate(['a','b','c','d']):
    print(i)
//Operation results:
(0, 'a')
(1, 'b')
(2, 'c')
(3, 'd')
for i in enumerate({'x':1,'y':2}):
    print(i)
//Operation results:
(0, 'y')
(1, 'x')

format() formatted output

globals() gets the dictionary of global variables and locals() gets the dictionary of local variables in the namespace where the method is executed.

def func():
    x = 1
    y = 2
    print(locals())  #Print names in local scope
    print(globals()) #Print names in global scope

hash() gets the hash value, which is used to verify the integrity of the data and is irreversible.

s='hello'
print(hash(s))#-6379790348615061731
s='h'
print(hash(s))#5735203904575971755

help() Get help.

hex() to hexadecimal

print(hex(10))#0xa
print(hex(11))#0xb

If id() looks at the unique id number, is is to determine whether the id is the same.

print(id('asdf'))
a=1
b=2
print(id(a))
print(id(b))
print(a is b)
x='a'
y='a'
print(id(x))
print(id(y))
print(x is y)

input() input

iter() converts an iterative object into an iterator.

len() Statistical Length

max(),min() maximum and minimum

zip() zipper function? zip converts the two incoming parameters into iteratable objects, with next() on each side being placed in a tuple.

l1=[1,2,3,4]
s='hel'
for i in zip(l1,s):
    print(i)
//Operation results:
(1, 'h')
(2, 'e')
(3, 'l')

sorted() next the iteratable object once and then ascend to the list.

l=[3,4,1,0,9,10]
print(sorted(l)) #The return value is a list and the default is ascending order
print(sorted(l,reverse=True)) #Descending order

map() mapping. Each number on the right maps a new list according to the rules on the left.

l=[1,2,3,7,5]
m=map(lambda item:item**2,l)
print(m)#<map object at 0x00000000027CDD68>
print(list(m))#print(list(m))

from functools import reduce merge

from functools import reduce #merge
l=list(range(100))
print(l)
print(reduce(lambda x,y:x+y,l,100))#5050#Reduc can pass multiple values

filter filtering

name_l=[
    {'name':'egon','age':18},
    {'name':'dragonFire','age':1000},
    {'name':'gaoluchuan','age':9000},
    {'name':'fsw','age':10000},
]

f=filter(lambda d:d['age'] > 100,name_l)#Return value on the left ture filter out
print(list(f))#[{'name': 'dragonFire', 'age': 1000}, {'name': 'gaoluchuan', 'age': 9000}, {'name': 'fsw', 'age': 10000}]

oct() octal

open() Gets the file handle

　　pow(x,y,z),x**y%z

range() to obtain iterative objects

rper() also shows that str is more humane

reversed() inversion order

slice() slices, which are not usually used

vars() returns the name of the local namespace in dictionary form.

_ import_ Imports strings

__import__('time')

Compoile () compiles strings into bytecodes and runs.

Exc () executes code or compiled string without return value

eval() converts an expression in a string to a python expression with a return value

round(x,[,n]) rounds off the value of x, n denotes decimal points.

Anonymous function

Comparing the salaries of several teachers, who gets the highest salary?

salaries={
    'egon':3000,
    'alex':100000000,
    'wupeiqi':10000,
    'yuanhao':250
}

max() is used directly to get the maximum value of the key, and value is used to get the most money. How to compare money and get the corresponding key of the money?

def get_value(k):
    return salaries[k]
print(max(salaries,key=get_value))#alex

Here, max transforms the incoming value into an iterative object, takes one value at a time and passes it to the function on the right, then compares it, and finally comes to the person whose maximum value is output to the maximum value.

The get_value function we defined here is very simple. It has only a single function and is completely unnecessary. We can use a simple lambda to complete it step by step.

lambda k:salaries[k]

Call of anonymous functions.

f=lambda k:salaries[k] #Anonymous functions can also assign a name, but this violates the original intention of anonymity.
print(f)#<function <lambda> at 0x0000000001D0CBF8>
print(f('egon'))#3000

It is also easier to solve the above problems.

print(max(salaries,key=lambda k:salaries[k]))#alex
print(min(salaries,key=lambda k:salaries[k]))#yuanhao

zip() function

print(salaries.keys(),salaries.values())
z=zip(salaries.values(),salaries.keys())
print(z)
print(max(z))#Take out the largest tuple
for i in z:
    print(i)

　　sorted()

print(sorted(salaries)) #The default is to follow the dictionary salaries Of key Sorted
print(sorted(salaries,key=lambda x:salaries[x]))
print(sorted(salaries,key=lambda x:salaries[x],reverse=True))
//Operation results:
['alex', 'egon', 'wupeiqi', 'yuanhao']
['yuanhao', 'egon', 'wupeiqi', 'alex']
['alex', 'wupeiqi', 'egon', 'yuanhao']

Posted by phpnoobie9 on Mon, 27 May 2019 11:39:55 -0700