python class variable in static method

Question

[updated]: Full code

I always get confused with pyhton's staticmethods but according to this (last answer), it should work!

getting error:

AttributeError: class MyConnection has no attribute 'myuser'

class MyConnection: def __init__(self, hostname, port, user, password): myhostname = hostname myport = port myuser = user mypassword = password isisessid = None @staticmethod def connect(): my_session = MyConnection() headers = {'content-type': 'application/json'} headers['Authorization'] = 'Basic ' + string.strip( base64.encodestring(MyConnection.myuser + ':' + MyConnection.mypassword)) body = json.dumps({'username': MyConnection.myuser, 'password': MyConnection.mypassword, 'services': ['platform', 'namespace']}) uri = '/session/1/session' connection = httplib.HTTPSConnection(MyConnection.myhostname, MyConnection.myport) connection.connect() try: connection.request('POST', uri, body, headers) response = connection.getresponse() my_session.isisessid = MyConnection.extract_session_id( response.getheaders()) except Exception, e: print e connection.close() except httplib.BadStatusLine, e: print e connection.close() return my_session

This question has nothing to do with static methods. The error is in your __init__: stackoverflow.com/a/18622179/429533 — Jace Browning
– Jace Browning, Commented Sep 4, 2013 at 19:29
@spinus: Thanks for the suggestion, its not my code - trying to build a car without reinventing the wheels! ;) — Peter
– Peter, Commented Sep 4, 2013 at 22:42

Óscar López · Accepted Answer · 2013-09-04 19:36:20Z

If the attributes are going to be static, don't initialize them in the initializer method, declare them outside at the class level, not at method level.

But why are you initializing class attributes in the initializer? every instance that you create will overwrite their values!

I believe you're confusing what instance attributes and class attributes are used for. Why don't you try using only instance attributes? all things considered, having static data is not a good idea. For example:

class MyConnection: def __init__(self, hostname, port, user, password): self.myhostname = hostname self.myport = port self.myuser = user self.mypassword = password @staticmethod def connect(): my_session = MyConnection() print my_session.myuser # just an example

Im creating an instance of class "my_session = MyConnection()" so I should use it to get its variables. duhh

spinus · Accepted Answer · 2013-09-04 19:36:24Z

You have to define attributes in a class scope (static attributes) or in instance scope (in __init__).

So in class scope it looks like:

class Cls(object): class_scope_attribute = 1 @staticmethod def method1(): print Cls.class_scope_attribute @classmethod def metdho2(cls): print cls.class_scope_attribute def method3(self): print Cls.class_scope_attribute print self.__class__.class_scope_attribute

In instance scope:

class Cls2(object): def __init__(self): self.instance_scope_attribute @staticmethod def method1(): # cannot access the instance_scope_attribute pass @classmethod def method2(cls): # cannot access the instance_scope_attribute pass def method3(self): print self.instance_scope_attribute

Look at the self in __init__ before variable name.

So, you have to add self. or move variables to class scope, but be careful as class scope attributes are shared by all instances.

Mario Rossi · Accepted Answer · 2013-09-04 20:01:49Z

If your purpose is really to make connect a @staticmethod, then initialize myhostname,myport, myuser, and mypassword at the class level, like in:

 class MyConnection: myhostname= hostnameValue myport= portValue myuser= userValue mypassword= passwordValue @staticmethod def connect(): my_session = MyConnection() headers = {'content-type': 'application/json'} headers['Authorization'] = 'Basic ' + string.strip( base64.encodestring( MyConnection.myuser + ':' + MyConnection.mypassword ) ) body = json.dumps({'username': MyConnection.myuser, 'password': MyConnection.mypassword,'services': ['platform', 'namespace']}) my_session.connection = httplib.HTTPSConnection(MyConnection.myhostname, MyConnection.myport) my_session.connection.connect() MyConnection.connect()

Alternatively, you can leave them in None and give them a value before calling connect().

If you want to make connect an instance method, then you are pretty much there. You just need to remove decorator @staticmethod, and do a few other changes:

 class MyConnection: def __init__(self, hostname, port, user, password): self.myhostname = hostname self.myport = port self.myuser = user self.mypassword = password def connect(): headers = {'content-type': 'application/json'} headers['Authorization'] = 'Basic ' + string.strip( base64.encodestring(self.myuser + ':' + self.mypassword) ) body = json.dumps({'username': self.myuser, 'password': self.mypassword, 'services': ['platform', 'namespace']}) connection = httplib.HTTPSConnection(self.myhostname, self.myport) connection.connect() my_session= MyConnection(hostnameValue,portValue,userValue,passwordValue) my_session.connect()

shivaraj karki · Accepted Answer · 2020-09-04 12:13:29Z

classmethod and static method cannot access varibles declared in __init__() method. Because classmethod and staticmethod bound to the class and not the object of the class, hence they take class parameters that points to the class and not the object instance.

__init__() creates object instance, hence variables declared in __init__() cannot be accessed by classmethod and staticmethod, unless they are declared as class variables.

They can modify a class state that would apply across all the instances of the class. For example they can modify a class variable that will be applicable to all the instances.

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