tkinter.TclError: unknown option

Question

Update: It was just a typo while creating btComputePayment.

SOLVED

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I'm learning Python using the book "Introduction to Programming Using Python (Pearson 2013)".

Currently I'm doing an exercise in which I have to code a loan calculator in Tkinter.

I can't seem to get the following code to work:

from tkinter import *

class LoanCalculator:
    def __init__(self):
        window = Tk()
        window.title("Loan Calculator")

        # Create labels
        Label(window, text = "Annual Interest Rate").grid(row = 1, column = 1, sticky = W)
        Label(window, text = "Number of Years").grid(row = 2, column = 1, sticky = W)
        Label(window, text = "Loan Amount").grid(row = 3, column = 1, sticky = W)
        Label(window, text = "Monthly Payment").grid(row = 4, column = 1, sticky = W)
        Label(window, text = "Total Payment").grid(row = 5, column = 1, sticky = W)

        # Create entries
        self.annualInterestRateVar = StringVar()
        Entry(window, textvariable = self.annualInterestRateVar, justify = RIGHT).grid(row = 1, column = 2)

        self.numberOfYearsVar = StringVar()
        Entry(window, textvariable = self.numberOfYearsVar, justify = RIGHT).grid(row = 2, column = 2)

        self.loanAmountVar = StringVar()
        Entry(window, textvariable = self.loanAmountVar, justify = RIGHT).grid(row = 3, column = 2)

        self.monthlyPaymentVar = StringVar()
        lblMonthlyPayment = Label(window, textvariable = self.monthlyPaymentVar, justify = RIGHT).grid(\
            row = 4, column = 2)

        self.totalPaymentVar = StringVar()
        lblTotalPayment = Label(window, textvariable = self.totalPaymentVar, justify = RIGHT).grid(\
            row = 4, column = 2)

        btComputePayment = Label(window, text = "Compute Payment", command = self.computePayment).grid(\
            row = 6, column = 2, sticky = E)

        window.mainloop()

    def computePayment(self):
        monthlyPayment = self.getMonthlyPayment(
            float(self.loanAmountVar.get()),
            float(self.annualInterestRateVar.get()) / 1200,
            int(self.numberOfYearsVar.get()))

        # Set monthly payment
        self.monthlyPaymentVar.set(format(monthlyPayment, "10.2f"))
        totalPayment = float(self.monthlyPaymentVar.get()) * 12 \
        * int(self.numberOfYearsVar.get())

        # Set total payment
        self.totalPaymentVar.set(format(totalPayment, "10.2f"))

    def getMonthlyPayment(self, loanAmount, monthlyInterest, numberOfYears):
        monthlyPayment = loanAmount * monthlyInterest / (1 - 1 / (1 + monthlyInterest) ** (numberOfYears * 12))
        return monthlyPayment

LoanCalculator()

Here's the full Traceback:

/Library/Frameworks/Python.framework/Versions/3.3/bin/python3 "/Users/narek_a/Dropbox/Python/PycharmProjects/Introduction to Programming/Chapter 9.py"
Traceback (most recent call last):
  File "/Users/narek_a/Dropbox/Python/PycharmProjects/Introduction to Programming/Chapter 9.py", line 421, in <module>
    LoanCalculator()
  File "/Users/narek_a/Dropbox/Python/PycharmProjects/Introduction to Programming/Chapter 9.py", line 398, in __init__
    btComputePayment = Label(window, text = "Compute Payment", command = self.computePayment).grid(\
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/tkinter/__init__.py", line 2596, in __init__
    Widget.__init__(self, master, 'label', cnf, kw)
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/tkinter/__init__.py", line 2075, in __init__
    (widgetName, self._w) + extra + self._options(cnf))
_tkinter.TclError: unknown option "-command"

Process finished with exit code 1

Any ideas?

Thanks

Answer 1

You are using a Label instead of a Button in line 33. Labels don't accept the argument "command" in the constructor. Buttons use the "command" argument for the callback of what they do when you click in the button.