How to pass variables between methods in the same class in Python

问题

I don't think I'm using class variables correctly. Inside the ClientFormPage class, I initialize the active_form to 'f1_form'. After I post the first form, I'd like to advance the active_form to 'f2_form', however it keeps resetting to 'f1_form'. What is the best way to do this?

class ClientFormPage(PageHandler):
    active_form = 'f1_form'

    def render_form(self, f1='hidden', f2='hidden', **kw):
        self.render('clientforms.html', form1=f1, form2=f2, **kw)

    def get(self):
        self.render_form(f1='')

    def get_form2(self):
        self.render_form(f2='')

    def post(self):
        if self.active_form == 'f1_form':
            foo = self.request.get('foo')
            if not foo:
                self.render_form(f1_form='', foo=foo, 
                                 foo_error='has-error has-feedback')
            else:
                self.active_form = 'f2_form' # This assignment is not sticking
                self.get_form2()
                return

        if self.active_form == 'f2_form':
            bar = self.request.get('bar')
            if not bar:
                self.render_form(f1_form='', bar=bar, 
                                 bar_error='has-error has-feedback')
            else:
                self.active_form = 'f3_form'
                self.get_form3()
                return

回答1:

If I understand your code and comment well, You want to preserve state (active_form) between requests. To do this you have to use cookies.

You cannot save state in your webapp2 request handler class between requests. For every request a new handler class is created.

See the docs: http://webapp-improved.appspot.com/api/webapp2_extras/sessions.html

An alternative approach is to save the name of your active form in a hidden input of your HTML form.

<input type="hidden" name ="active_form" value="{{ active_form }}" >

回答2:

You could use the __init__ magic method

class ClientFormPage(PageHandler):
    def __init__(self):
        self.active_form = 'f1_form'

This will allow you to have instance specific attributes, instead of class attributes as you have in your original code.

Quick demo on the difference:

Python - why use "self" in a class?

回答3:

class myClass(object):

def __init__(self):

def helper(self, jsonInputFile):
    values = jsonInputFile['values']
    ip = values['ip']
    username = values['user']
    password = values['password']
    return values, ip, username, password

def checkHostname(self, jsonInputFile):
   values, ip, username, password = self.helper
   print values
   print '---------'
   print ip
   print username
   print password

the init method initializes the class. the helper function just holds some variables/data/attributes and releases them to other methods when you call it. Here jsonInputFile is some json. the checkHostname is a method written to log into some device/server and check the hostname but it needs ip, username and password for that and that is provided by calling the helper method.

来源：https://stackoverflow.com/questions/23051746/how-to-pass-variables-between-methods-in-the-same-class-in-python