I'm new to python and Kivy programming so getting trouble and may be asking simple question here, but its a big hurdle for me now. I am developing a GUI with kivy. I have some TextInputs which get numeric value. after all text inputs , I have a 'OK' button which gets all value and process them. I'm getting error in calling the function from same class in .kv file.

main.py file:

# File name: jwelkreator.py
import kivy
kivy.require('1.7.0')
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.anchorlayout import AnchorLayout

Builder.load_file('simpleForm.kv')
...
...

class JwelKreator(AnchorLayout):
    pass

class JwelKreatorApp(App):
    def build(self):
        return JwelKreator()

if __name__=="__main__":
    JwelKreatorApp().run()

main kv file

# File name: jwelkreator.kv
#:kivy 1.7.0
<JwelKreator>:
    AnchorLayout:
        anchor_x: 'left'
        anchor_y: 'top'
        MyLayout:
            id: _tool_box
            size_hint: None,0.75
            width: 300
   ...
   ...

simpleForm.py for text inputs.

import kivy

from kivy.app import App
from kivy.lang import Builder
from kivy.config import Config

from kivy.uix.boxlayout import BoxLayout

class LblTxt(BoxLayout):
    pass
class MyLayout(BoxLayout):
    def print_something(self):
        print "Hello"

simpleForm.kv TextInput Layout

<LblTxt@BoxLayout>:
    id:LblTxtid
    orientation: 'horizontal'      
    lblTxtIn: 'default'
    theTxt: iAmTxt
    Label:
        text: root.lblTxtIn
        size_hint: 1,0.5
    TextInput:
        id: iAmTxt  
        multiline: False
        hint_text: "numeric only"           
        input_filter: 'int'
        size_hint: 0.5,None
        height: 30
<MyLayout@BoxLayout>:  
    orientation: 'vertical'

    LblTxt:   
        id: lt0
        lblTxtIn: 'Base Layers'

    LblTxt:   
        id: lt1
        lblTxtIn: 'Base exposer time(ms)'

    LblTxt:   
        id: lt2
        lblTxtIn: 'Min Support Height(mm)'

    LblTxt:   
        id: lt3
        lblTxtIn: 'Support Layers'

    LblTxt:   
        id: lt4
        lblTxtIn: 'Support exposer time(ms)'

    LblTxt:   
        id: lt5
        lblTxtIn: 'Job exposer time(ms)'

    Label:
        text:"Number of Layers"
    Button:
        text: 'OK'
        size_hint: 0.5,None
        height: 30
        on_release: root.print_something()

While I press 'OK' button, attribute Error Generated.

Traceback (most recent call last):
   File "jwelkreator.py", line 21, in <module>
     JwelKreatorApp().run()
   File "/usr/lib/python2.7/dist-packages/kivy/app.py", line 600, in run
     runTouchApp()
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 454, in runTouchApp
     EventLoop.window.mainloop()
   File "/usr/lib/python2.7/dist-packages/kivy/core/window/window_pygame.py", line 325, in mainloop
     self._mainloop()
   File "/usr/lib/python2.7/dist-packages/kivy/core/window/window_pygame.py", line 231, in _mainloop
     EventLoop.idle()
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 297, in idle
     self.dispatch_input()
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 284, in dispatch_input
     post_dispatch_input(*pop(0))
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 253, in post_dispatch_input
     wid.dispatch('on_touch_up', me)
   File "_event.pyx", line 285, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:4184)
   File "/usr/lib/python2.7/dist-packages/kivy/uix/button.py", line 140, in on_touch_up
     self.dispatch('on_release')
   File "_event.pyx", line 281, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:4134)
   File "simpleForm.kv", line 1, in <module>
     <LblTxt@BoxLayout>:
 AttributeError: 'MyLayout' object has no attribute 'print_something'

I am stuck here and not getting way to solve it. Is there anything I'm missing?

EDIT: @eyllanesc: as per your suggestion, I've removed @BoxLayout from my kv class name. I'm getting error from my main .kv file as I'm calling MyLayout from main.kv

MyLayout:
            id: _tool_box
            size_hint: None,0.75
            width: 300

ERROR:

Traceback (most recent call last):
   File "jwelkreator.py", line 21, in <module>
     JwelKreatorApp().run()
   File "/usr/lib/python2.7/dist-packages/kivy/app.py", line 577, in run
     root = self.build()
   File "jwelkreator.py", line 18, in build
     return JwelKreator()
   File "/usr/lib/python2.7/dist-packages/kivy/uix/anchorlayout.py", line 62, in __init__
     super(AnchorLayout, self).__init__(**kwargs)
   File "/usr/lib/python2.7/dist-packages/kivy/uix/layout.py", line 61, in __init__
     super(Layout, self).__init__(**kwargs)
   File "/usr/lib/python2.7/dist-packages/kivy/uix/widget.py", line 163, in __init__
     Builder.apply(self)
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1429, in apply
     self._apply_rule(widget, rule, rule)
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1534, in _apply_rule
     self._apply_rule(child, crule, rootrule)
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1496, in _apply_rule
     cls = Factory_get(cname)
   File "/usr/lib/python2.7/dist-packages/kivy/factory.py", line 91, in __getattr__
     raise FactoryException('Unknown class <%s>' % name)
 kivy.factory.FactoryException: Unknown class <MyLayout>

Problem

You are getting AttributeError: 'MyLayout' object has no attribute 'print_something' because it cannot find the function, print_something.

Solution

Please refer to the explanations, example and output for details.

Explanations

jwelkreator.py

Add from simpleForm import MyLayout
Remove Builder.load_file('simpleForm.kv')

jwelkreator.kv

Add #:include simpleForm.kv to include an external kivy file.

include <file> - Kivy Language

Includes an external kivy file. This allows you to split complex widgets into their own files.

simpleForm.py

You don't have to define the dynamic class, LblTxt(BoxLayout) since you have it defined in your kv file.

Dynamic Classes - Programming Guide » Kv language

This class, created just by the declaration of this rule, inherits from the Button class and allows us to change default values and create bindings for all its instances without adding any new code on the Python side.

simpleform.kv

Since in the Python script, simpleForm.py, you have already defined class MyLayout is of BoxLayout, you don't to inherit it in the kv file. Replace <MyLayout@BoxLayout> with <MyLayout>

Example

jwealkreator.py

from kivy.app import App
from kivy.uix.anchorlayout import AnchorLayout
from simpleForm import MyLayout


class JwelKreator(AnchorLayout):
    pass


class JwelKreatorApp(App):

    def build(self):
        return JwelKreator()


if __name__ == "__main__":
    JwelKreatorApp().run()

jwealkreator.kv

# File name: jwelkreator.kv
#:kivy 1.10.0
#:include simpleform.kv

<JwelKreator>:
    anchor_x: 'left'
    anchor_y: 'top'
    MyLayout:
        id: _tool_box
        size_hint: None,0.75
        width: 300

simpleForm.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout


class MyLayout(BoxLayout):
    def print_something(self):
        print("Hello")


class SimpleFormApp(App):

    def build(self):
        return MyLayout()


if __name__ == "__main__":
    SimpleFormApp().run()

simpleform.kv

#:kivy 1.10.0

<LblTxt@BoxLayout>:
    id:LblTxtid
    orientation: 'horizontal'
    lblTxtIn: 'default'
    theTxt: iAmTxt
    Label:
        text: root.lblTxtIn
        size_hint: 1,0.5
    TextInput:
        id: iAmTxt
        multiline: False
        hint_text: "numeric only"
        input_filter: 'int'
        size_hint: 0.5,None
        height: 30

<MyLayout>:
    orientation: 'vertical'

    LblTxt:
        id: lt0
        lblTxtIn: 'Base Layers'

    LblTxt:
        id: lt1
        lblTxtIn: 'Base exposer time(ms)'

    LblTxt:
        id: lt2
        lblTxtIn: 'Min Support Height(mm)'

    LblTxt:
        id: lt3
        lblTxtIn: 'Support Layers'

    LblTxt:
        id: lt4
        lblTxtIn: 'Support exposer time(ms)'

    LblTxt:
        id: lt5
        lblTxtIn: 'Job exposer time(ms)'

    Label:
        text:"Number of Layers"
    Button:
        text: 'OK'
        size_hint: 0.5,None
        height: 30
        on_release: root.print_something()