tkinter new class can't use .get()/float()

Question

I have defined a new Entry subclass: NewEntry, but it can't get the numbers which are put in it. How can I fix this?

When I click the button, the error message is showed:

ValueError: could not convert string to float:

from Tkinter import *
root = Tk()                                                                                                                              

class NewEntry(Entry):
    def __init__(self,parent,cusdef='1'):      #Initiation default number is '1'                                      
        Entry.__init__(self,parent)
        self.cusdef = cusdef
        v=StringVar()
        v.set(self.cusdef)
        self = Entry(self,textvariable=v)
        self.pack()
        return

def GetNum():
    a=e.get()
    print float(a)
    return

e = NewEntry(root)
e.pack(fill='x')

button = Button(root,command=GetNum)
button.pack(fill='x')
root.mainloop()

Answer 1

You seem to be trying to initialize your Entry subclass here:

self = Entry(self,textvariable=v)
self.pack()

But instead, you're merely overwriting the variable called self and creating a new Entry which gets discarded.

Instead you need to do the Entry.__init__ call once, with the correct arguments:

class NewEntry(Entry):
    def __init__(self,parent,cusdef='1'):
        self.cusdef = cusdef
        v=StringVar()
        v.set(self.cusdef)
        Entry.__init__(self,parent, textvariable=v)
        self.pack()
        return