One: namespace
class Person:
Country = 'Chinese' # static variable
print(Person.Country)
alex = Person() # creates an empty namespace
alex.name = 'alex' # object
alex.Country = 'Thai'
egon = Person ()
stay.name = 'stay'
# class name. static variable object. property name
# Can the class name call the properties of the object? No
# Can an object call properties in a class? Yes
print(Person.Country)
print(alex.Country)
print(egon.Country)
print result
Note: The class name cannot call the property of the object (it is not clear which object property it is, two countries)
The object name can call the property in the class (alex.country)
Because there is an association between objects and classes So the object can find the class But the class can't find the object
2: Object. Attribute namespace search (first in your own namespace, then in the class namespace)
#Use the class name. The property will only look for the static variable name in the class
#Using objects. Properties will first look for names in the object's own namespace
# If you can't find it, go to the memory space of the class to find it
class Person:
Country = 'Chinese' # static variable
alex = Person()
egon = Person ()
print(alex.Country)
alex.Country = 'Indian'
print(alex.Country)
Person.Country
# As long as you use static variables, use the class name to call
Note: When you use static variables, use the class name to call
Example 1
class Person:
money = 0
mother = Person()
father = Person()
Person.money += 1000
Person.money += 1000
print(Person.money)
print(mother.money)
print(father.money)
Print result: 2000, 2000, 2000
Example 2
class Person:
money = [1]
mother = Person()
father = Person()
mother.money[0] += 1000 [0] means index
father.money[0] += 1000[0] means index
print(mother.money)
print(father.money)
print(Person.money)
print result [2001], [2001], [2001]
Note: [0] means index, += 1000 means index plus.
Example 3
class Person:
money = [0]
mother = Person()
father = Person()
mother.money = [1000]
father.money = [2000]
print(mother.money)
print(father.money)
print(Person.money)
Print result: [1000], [2000], [0] In example 3, the index change only changes the calling class attribute, but this question does not change.
Example 4
a = 1 a = 2 print(a) a = [1] a.append(2) print(id(a)) a[0] = 10 print(id(a)) print(a) a = [1] a = [2]
Print result: 2, 40615688, 40615688, [10,2]
Example 5:
Write a class that can count how many objects this class has been instantiated.
All objects share this result
init static variable
class Foo:
num = 0
def __init__(self):
Foo.num += 1
f1 = Foo()
print(Foo.num)
f2 = Foo()
print(Foo.num)
print(f1.num)
Combination: circle and teacher combination example
Combining two classes What is composition: properties of one class object are objects of another class A matter of two classes: there is a "what is what" relationship between classes round class rings and circles A torus is also a class Properties Great Circle Radius and Small Circle Radius Find the area of a ring to find the perimeter
from math import pi
class Circle:
def __init__(self,r):
self.r=r
def area(self):
return pi*(self.r**2)
class Ring:
def __init__(self,outer,inner):
self.outer=Circle(outer)
self.inner=Circle(inner)
def area(self):
return self.outer.area()-self.inner.area()
r=Ring(10,3)
c=Circle(11)
print(Ring.area(r))
print(r.area())
Example: Teacher's Birthday Combination
reference answer
teacher name sex course (course) birth
birthday date
class Birthday:
def __init__(self,year,month,day):
self.year = year
self.month = month
self.day = day
class Teacher:
def __init__(self,name,sex,course,birth):
self.name = name
self.sex = sex
self.course = course
self.birth = birth # birth is an object
birth = Birthday(1960,3,7) # birth is an object of the Birthday class
alex = Teacher('alex','male','python',birth)
# alex.birth = birth
# time
'1960-3-7'
# Teacher's age 2018 - 1960
print(birth)
import time
if birth.month == time.localtime().tm_mon and \
birth.day == time.localtime().tm_mday:
print('Happy Birthday')
print(time.localtime().tm_year - birth.year)
Write it yourself:
class Birthday:
def __init__(self,year,month,day):
self.year=year
self.month=month
self.day=day
class Teacher:
def __init__(self,name,course,birth):
self.name=name
self.course=course
self.birth=birth
birth=Birthday(1960,4,4)
zhen=Teacher('zhen','python',birth)
# print(Birthday.year())
print(zhen.birth.year)
print(birth.year)