Consider the following information about the pharmacies, patients and drugs: ● (1) Patients are identified by an SSN, and their names, addresses, and ages must be recorded. ● (2) Doctors are identified by an SSN. For each doctor, the name, specialty, and years of experience must be recorded. ● (3) Each pharmaceutical company (制药公司) is identified by name and has a phone number. ● (4) For each drug, the trade name and formula（成份）must be recorded. Each drug is produced by a given pharmaceutical company, and the trade name identifies a drug uniquely from among the products of that company. ● (5) Each pharmacy(药房) has a name, address, and phone number. Each pharmacy is identified by ID. ●(6) Every patient has a primary doctor. Every doctor has at least one patient. ● (7) Each pharmacy sells several drugs and has a price for each. A drug could be sold at several pharmacies, and the price could vary from one pharmacy to another. ● (8) Doctors prescribe drugs for patients. A doctor could prescribe one or more drugs for several patients, and a patient could obtain prescriptions from several doctors. Each prescription has a date and a quantity associated with it. ●(9) Pharmaceutical companies have long term contracts with pharmacies. A pharmaceutical company can contract with several pharmacies, and a pharmacy can contract with several pharmaceutical companies. For each contract, you have to store a start date, an end date. 用ER图进行描述用python代码表示

根据上述信息，可以设计以下实体和关系：

实体：
- Patient (SSN, Name, Address, Age)
- Doctor (SSN, Name, Specialty, Years of Experience)
- Pharmaceutical Company (Name, Phone Number)
- Drug (Trade Name, Formula)
- Pharmacy (ID, Name, Address, Phone Number)

关系：
- Produces (Pharmaceutical Company, Trade Name)
- Sells (Pharmacy, Trade Name, Price)
- Prescribes (Doctor, SSN, Trade Name, Patient, SSN, Date, Quantity)
- Contracts (Pharmaceutical Company, Pharmacy, Start Date, End Date)
- Has Primary Doctor (Patient, SSN, Doctor, SSN)

以下是用Python代码表示的实体和关系：

# 实体类
class Patient:
    def __init__(self, ssn, name, address, age):
        self.ssn = ssn
        self.name = name
        self.address = address
        self.age = age

class Doctor:
    def __init__(self, ssn, name, specialty, years_of_experience):
        self.ssn = ssn
        self.name = name
        self.specialty = specialty
        self.years_of_experience = years_of_experience

class PharmaceuticalCompany:
    def __init__(self, name, phone_number):
        self.name = name
        self.phone_number = phone_number

class Drug:
    def __init__(self, trade_name, formula, pharmaceutical_company):
        self.trade_name = trade_name
        self.formula = formula
        self.pharmaceutical_company = pharmaceutical_company

class Pharmacy:
    def __init__(self, id, name, address, phone_number):
        self.id = id
        self.name = name
        self.address = address
        self.phone_number = phone_number

# 关系类
class Produces:
    def __init__(self, pharmaceutical_company, drug):
        self.pharmaceutical_company = pharmaceutical_company
        self.drug = drug

class Sells:
    def __init__(self, pharmacy, drug, price):
        self.pharmacy = pharmacy
        self.drug = drug
        self.price = price

class Prescribes:
    def __init__(self, doctor, patient, drug, date, quantity):
        self.doctor = doctor
        self.patient = patient
        self.drug = drug
        self.date = date
        self.quantity = quantity

class Contracts:
    def __init__(self, pharmaceutical_company, pharmacy, start_date, end_date):
        self.pharmaceutical_company = pharmaceutical_company
        self.pharmacy = pharmacy
        self.start_date = start_date
        self.end_date = end_date

class HasPrimaryDoctor:
    def __init__(self, patient, doctor):
        self.patient = patient
        self.doctor = doctor

注意：上述代码只是一种示例实现，具体实现方式可能会因具体情况而有所不同。