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

Question

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

score 0 · Answer 1 · edited May 23 '17 at 12:21

0

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?

edited May 23 '17 at 12:21

Community

1
1

answered Apr 14 '14 at 04:05

C.B.

8,096
5
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I just deleted my class variable line and replaced it with the two __init__ lines. I'm not clear how webapp2 calls this, but I get a TypeError: __init__() takes exactly 1 argument (3 given). This prompted me to change to def __init__(self, foo, bar). This time, I get AttributeError: 'NoneType' object has no attribute 'route'. I'm not sure if I've provided enough to figure this out. Anything sound obvious? – bholben Apr 14 '14 at 04:28
1

@bholben It looks like `PageHandler` objects are passed arguments when instantiated. Change the definition to `def __init__(self, *args, **kwargs):` and insert before your attribute creation `super(PageHandler, self).__init__(*args, **kwargs)`. – Matthew Trevor Apr 14 '14 at 07:07

voscausa · Accepted Answer · 2014-04-14T11:28:56.783

0

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 }}" >

edited Apr 14 '14 at 11:28

answered Apr 14 '14 at 11:19

voscausa

11,253
2
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67

This hidden input approach looks like exactly what I'm looking for, however it does not seem to work for me. I've added this to my html template: . I've also added this under my ClientFormPage class: def post(self): active_form = self.request.get('active_form') self.response.write('Active Form: ' + active_form) – bholben Apr 15 '14 at 03:30
When I view the final write, it only displays 'Active Form: ' with no active_form value showing up. I've not figured out where the value went. Am I missing something with the hidden input? – bholben Apr 15 '14 at 03:36
It should be easy to debug. First look in your HTML form if the hidden input holds the active form value. – voscausa Apr 15 '14 at 11:48

score 0 · Answer 3 · answered Jun 28 '17 at 14:12

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.

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

3 Answers3

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