如何从列表动态生成类? [英] How do you dynamically generate classes from a list?
问题描述
我想创建一个类,该类会自动为以后可以访问的值添加一个持有人,以便当我运行cd.orders或cd.users时,它将返回或为我刚刚提供的每个表提供一个数据框
I want to create a class that automatically adds a holder for values that I can access in the future so that when I run cd.orders or cd.users it will return or give me a dataframe of each of the tables I just queried against.
这里是我的示例代码:
class samplecode:
def __init__(self,credentials):
c = credentials ('DATABASE', 'USER', 'PASSWORD', 'HOST', 'PORT', 'SCHEMA')
print('credentials loaded')
self.connection_string = "postgresql://%s:%s@%s:%s/%s" % (c.USER,
c.PASSWORD,
c.HOST,
str(c.PORT),
c.DATABASE)
self.engine = sa.create_engine(connection_string)
print('redshift connected')
self.data = []
def get_db(self,tables):
for t in tables:
self.data = pd.read_sql_query('SELECT * FROM database.{} limit 10'.format(t),engine)
print(self.data.head(2))
cd = samplecode(credential)
# llf.view_obj
cd.get_db(['orders','user'])
我希望是在cd.get_db之后,它将返回或给我两个实例/对象。当我键入dir(cd)
What I am hoping is that after cd.get_db it will return or give me two instances/objects. When I type dir(cd)
我应该能够执行cd.orders和cd.user,并且如果我在列表cd.xyz中添加更多内容。
i should be able to do cd.orders and cd.user and if I add more to the list cd.xyz.
我尝试了此操作,但只能访问最新的df,因为它会覆盖另一个df
I tried this but could only access the most recent df since it overwrites the other df
class Wrapper(object):
def __init__(self, data):
self.data = data
def __getattr__(self, attr):
return [d[attr] for d in self.data]
# Wrapper([{'x': 23}, {'x': 42}, {'x': 5}])
instancelist = ['orders','user']
for i in instancelist:
data = Wrapper([{i:'a'}])
cd.data
Hopnig对此事提供了帮助和澄清!
Hopnig for help and clarification on the matter thanks!
否则,请考虑以下事项:
or if this is confusing, consider the following:
class BaseClass:
def __init__(self):
self.a = []
self.b = []
def execute_query(self,table_name):
for tables in table_name:
self.table_name = run_query()
table_list = ['D','E','F']
test = BaseClass
test.execute_query(table_list)
dir(test)
[
'a',
'b',
'D',
'E',
'F'
'__class__',
'__delattr__',
'__dict__',
'__dir__',
]
推荐答案
听起来您正在寻找 setattr
内置的。您可以调用它以将属性(以字符串形式)分配给对象。因此,不必打印表,您可以将每个表分配给以表名称命名的属性:
It sounds like you're looking for the setattr
builtin. You can call it to assign an attribute (given as a string), to an object. So rather than printing out your tables, you can assign each one to an attribute named after the table's name:
def get_db(self,tables):
for t in tables:
data = pd.read_sql_query('SELECT * FROM database.{} limit 10'.format(t), engine))
setattr(self, t, data)
您还可以朝另一个方向做事,并查找属性触发数据库查询。为此,您想向您的课程添加 __ getattr __
方法。
You could also do things in the other direction, and have the lookup of an attribute trigger a database query. For that you'd want to add a __getattr__
method to your class. That would be called when an attribute was looked up and not found normally.
def __getattr__(self, name):
data = pd.read_sql_query('SELECT * FROM database.{} limit 10'.format(name), engine))
setattr(self, name, data) # save to an attribute so we don't need to query it again
return data
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