OOP Cheat Sheet (DRAFT) by cgeeeeh

#类的名字应该用大写字母
class Employee:
  #给一些定义
  """ define a class for all employee
instances in a company ”””
  #没啥内容就写pass
  pass

#创建一个实体
variable_name = Employee()

instance attributes 是每个实体都有自己的
# Provide attributes and assign values to the instances
emp1.firstName = "Maria"
emp1.lastName = "Rena"
emp1.basicSalary = 12000
emp1.allowance = 5000

class attributes belong to the class itself, and are thus shared among all instances of the class
如果先声明instant attribute，再声明class attribute。那不会覆盖原来的instant attribute。
但如果原来在类里声明了一个类attribute，在后面再修改，那原来的值确实会被覆盖

obj.__dict__返回【实体】和它的所有方法
class.__dict__返回【类】的所有方法和属性

instant method是自定义的
class Employee:
  bonusPercent = 0.2
  # Define an instance method that takes no arguments
  def calculateBonus(self):
    return self.salary * Employee.bonusPercent

如何更改bonusPercent的默认值？用类的调用来改
Employee.bonusPercent=0.3

Constructor & Destructor Method 是内置的建立和销毁函数
__init__，__del__，__str__

#这段代码有条件才执行，如果不执行的话这个实例四个attribute都不会有
def __init__ (self, first = None, last = None, salary = None, allowances = None):
  if first!= None and last!= None and salary!= None and allowances!= None:
    self.firstName = first
    self.lastName = last
    self.salary = salary
    self.allowances = allowances
    print("Object initialized with supplied values")

import _pickle as cpickle
class stock:
  def __init__(self, name, lots):
  self.name = name
  self.lots = lots
  def __str__(self):
    return f’{self.name}=>{self.lots}'

#写入
s1 = stock("Apple",1500)
s2 = stock("Google",2000)
with open("s1.obj", "wb") as f:
cpickle.dump(s1/[s1,s2], f)

#加载
with open("s1.obj", "rb") as f:
  s1 = cpickle.load(f)
  print(s1)
with open("ss.obj", "rb") as f:
  data = cpickle.load(f)
  for each in data:
    print(each)

class employee:
  count=5
  def __init__(self,x):
    self.x=x
    self.count=self.count+1
    print ("this method is executed")
    print (self.count)
    print (employee.count)

emp1=employee("John")
emp1.count+=1
print(emp1.count)
print(employee.count)

结果是6，5，7，5。self.variable显示的是这个obj自己当前的值，class.variable显示的是他们共用的初始值

#把obj放进json再取出来
import json
from json import JSONEncoder

class stock(object):
  def __init__(self, name, lots):
    self.name = name
    self.lots = lots
  def __str__(self):
    return f’{self.name}=>{self.lots}'

class StockEncoder(JSONEncoder):
  def default(self, o):
  return o.__dict__

s1 = stock("Apple",1500)

# encode Object it
s1Json = json.dumps(s1, cls=StockEncoder, indent=4)
‘’’
json.loads() method can be used to parse a valid JSON string and convert it into a Python Dictionary.
‘’’
resultDict = json.loads(s1Json)
s1Obj = stock(**resultDict)

#json data写入/存储
with open("stockPrettyPrint.json", "w") as write_file:
  json.dump(s1, write_file,cls=StockEncoder, indent=4)
with open("stockPrettyPrint.json", "r") as read_file:
  s = json.load(read_file)
  PrettyJson = json.dumps(s, indent=4, separators=(',', ': '), sort_keys=True)

#Json, Dictionary, object
import json
from json import JSONEncoder

class stock(object):
  def __init__(self, name, lots):
    self.name = name
    self.lots = lots
  def __str__(self):
    return f'{self.name}=>{self.lots}’

class StockEncoder(JSONEncoder):
  def default(self, o):
    return o.__dict__
  def StockDecoder(obj):
    if '__type__' in obj and obj['__type__'] =='stock':
      return stock(obj['name'], obj['lots'])
    return obj

s2Obj = json.loads('{"__type__": "stock", "lots":2000, "name": "Google"}', object_hook=StockDecoder)

with open("stockPrettyPrint.json", "w") as write_file:
  json.dump([s2Obj], write_file,cls=StockEncoder, indent=4))
with open("stockPrettyPrint.json", "r") as read_file:
  print("Read JSON file")
  s = json.load(read_file)
  for each in s:
    each = stock(**each)
    print(each)

#把obj放进json再取出来
import json
from json import JSONEncoder

class stock(object):
  def __init__(self, name, lots):
    self.name = name
    self.lots = lots
  def __str__(self):
    return f’{self.name}=>{self.lots}'

class StockEncoder(JSONEncoder):
  def default(self, o):
  return o.__dict__

s1 = stock("Apple",1500)

# encode Object it
s1Json = json.dumps(s1, cls=StockEncoder, indent=4)
‘’’
json.loads() method can be used to parse a valid JSON string and convert it into a Python Dictionary.
‘’’
resultDict = json.loads(s1Json)
s1Obj = stock(**resultDict)

#json data写入/存储
with open("stockPrettyPrint.json", "w") as write_file:
  json.dump(s1, write_file,cls=StockEncoder, indent=4)
with open("stockPrettyPrint.json", "r") as read_file:
  s = json.load(read_file)
  PrettyJson = json.dumps(s, indent=4, separators=(',', ': '), sort_keys=True)

#Json, Dictionary, object
import json
from json import JSONEncoder

class stock(object):
  def __init__(self, name, lots):
    self.name = name
    self.lots = lots
  def __str__(self):
    return f'{self.name}=>{self.lots}’

class StockEncoder(JSONEncoder):
  def default(self, o):
    return o.__dict__
  def StockDecoder(obj):
    if '__type__' in obj and obj['__type__'] =='stock':
      return stock(obj['name'], obj['lots'])
    return obj

s2Obj = json.loads('{"__type__": "stock", "lots":2000, "name": "Google"}', object_hook=StockDecoder)

with open("stockPrettyPrint.json", "w") as write_file:
  json.dump([s2Obj], write_file,cls=StockEncoder, indent=4))
with open("stockPrettyPrint.json", "r") as read_file:
  print("Read JSON file")
  s = json.load(read_file)
  for each in s:
    each = stock(**each)
    print(each)