Loan_Calulator.py

from tkinter import *
fields=("Loan Amount","Number of installments","Rate of Intrest","Installment")
def calculate_installment(entries):
    r=(float(entries[fields[2]].get())/100)/12
    p=(float(entries[fields[0]].get()))
    n=(float(entries[fields[1]].get()))
    i=p*r*(1+r)**n/((1+r)**n-1)
    i=("%8.2f"%i).strip()
    
    entries[fields[3]].config(state=NORMAL)
    entries[fields[3]].delete(0,'end')
    entries[fields[3]].insert(0,i)
    entries[fields[3]].config(state=DISABLED)

def makeform(root,fields):
    entries={}
    for field in fields:
         row=Frame(root)
         lab=Label(row,width=22,text=field+": ",anchor="w")
         ent=Entry(row)
         ent.insert(0,"0")
         row.pack(side=TOP,fill=X,padx=5,pady=5)
         lab.pack(side=LEFT)
         ent.pack(side=RIGHT)
         entries[field]=ent
    entries[field].config(state=DISABLED)
    return entries
         
if(__name__=='__main__'):
    root=Tk()
    root.title("Emi Calulator")
    ents=makeform(root,fields)
    b1=Button(root,text="Emi",command=(lambda e=ents:calculate_installment(e)))
    b1.pack(side=LEFT,padx=5,pady=5)
    b2=Button(root,text="Exit",command=root.quit)
    b2.pack(side=LEFT,padx=5,pady=5)
    root.mainloop()