Python调用AnimalShelter类create方法缺参数，类初始化问题咨询

• 核心报错根源：类实例化方式错误。你当前的写法a = AnimalShelter是将类本身赋值给变量a，而非创建类的实例，手动调用__init__的方式不符合Python类实例化规范，导致调用实例方法时self参数没有被自动传入，系统会把你传入的i当成self参数，因此才会提示data参数缺失。
• 隐藏错误1：animal_shelter模块中__init__方法缩进错误，self.database = self.client['AAC']现在仅在无用户名密码的else分支中生效，当你传入用户名密码时不会执行这行代码，后续调用方法会找不到database属性报错。
• 隐藏错误2：模块中update、delete方法里引用的self.AAC是错误写法，应该替换为self.database，否则调用这两个方法时会直接报错。
• 可选优化点：create方法中使用的insert是pymongo旧版本API，新版本建议替换为insert_one避免弃用警告。

修正后的测试代码 #

from animal_shelter import AnimalShelter

username = "aacuser"
password = "Mulligan!23"
# 正确实例化类，直接传参即可，不需要手动调用__init__
a = AnimalShelter(username, password)

animal_data = [
    {
        "name":"Finn",
        "type":"dog"
    },
    {
        "name":"Max",
        "type":"cat"
    },
    {
        "name":"Cooper",
        "type":"dog"
    },
    {
        "name":"Mulligan",
        "type":"dog"
    }
]

for i in animal_data:
    a.create(i)

dogs = a.read( {"type":"dog"}  )
for dog in dogs:
    print(dog)

修正后的animal_shelter模块核心代码 #

from pymongo import MongoClient
from bson.objectid import ObjectId

class AnimalShelter(object):
    """ CRUD operations for Animal collection in MongoDB """

    def __init__(self, username, password):
        # Initializing the MongoClient. This helps to 
        # access the MongoDB databases and collections. 
        if username and password:
            self.client = MongoClient('mongodb://%s:%s@localhost:53937' % (username,password))
        else:
            self.client = MongoClient('mongodb://localhost:53937')
        # 调整缩进到if else分支外，所有场景都初始化database
        self.database = self.client['AAC']

    # Complete this create method to implement the C in CRUD.
    def create(self, data):
        if data is not None:
            # 替换为新API insert_one
            insert = self.database.animals.insert_one(data)  # data should be dictionary 
            if insert.acknowledged:
                return True
            else:
                return False           
        else:
            raise Exception("Nothing to save, because data parameter is empty")


    # Create method to implement the R in CRUD.
    def read(self,criteria=None):
        # If data applicable, it will return all rows which match criteria
        if criteria:
         # {'_id':False}, no ID will be placed in row(s)       
            data = self.database.animals.find(criteria,{"_id":False})
        else: 
            data = self.database.animals.find( {} , {"_id":False})
        return data
    
    # Create method to implement the U in CRUD
    def update(self, data, newData):
        if data is not None:
            # 修正为self.database
            return self.database.animals.update_one(data, {'$set': newData})
        else:
            print("Nothing to update, because data parameter is empty")
            return False

       
    # Create method to implement the D in CRUD
    def delete(self, data):
        if data is not None:
            # 修正为self.database，调整print位置到return之前
            res = self.database.animals.delete_one(data)
            print("data deleted")
            return res
        else:
            return False

内容的提问来源于stack exchange，提问作者sarahprince23