Jack - 1 year ago 168

Python Question

i'm very new to python and i would like to fix the "C" button so that it clears the last number on the display. For example 321 would become 32, i have tried a lot of things but i can't seem to get it to work, i would be very grateful if someone could get it working, thank you. Here is the code:

`from tkinter import *`

class Calc():

def __init__(self):

self.total = 0

self.current = ""

self.new_num = True

self.op_pending = False

self.op = ""

self.eq = False

def num_press(self, num):

self.eq = False

temp = text_box.get()

temp2 = str(num)

if self.new_num:

self.current = temp2

self.new_num = False

else:

if temp2 == '.':

if temp2 in temp:

return

self.current = temp + temp2

self.display(self.current)

def calc_total(self):

self.eq = True

self.current = float(self.current)

if self.op_pending == True:

self.do_sum()

else:

self.total = float(text_box.get())

def display(self, value):

text_box.delete(0, END)

text_box.insert(0, value)

def do_sum(self):

if self.op == "add":

self.total += self.current

if self.op == "minus":

self.total -= self.current

if self.op == "times":

self.total *= self.current

if self.op == "divide":

self.total /= self.current

self.new_num = True

self.op_pending = False

self.display(self.total)

def operation(self, op):

self.current = float(self.current)

if self.op_pending:

self.do_sum()

elif not self.eq:

self.total = self.current

self.new_num = True

self.op_pending = True

self.op = op

self.eq = False

def cancel(self):

self.eq = False

self.current = "0"

self.display(0)

self.new_num = True

def all_cancel(self):

self.cancel()

self.total = 0

def sign(self):

self.eq = False

self.current = -(float(text_box.get()))

self.display(self.current)

sum1 = Calc()

root = Tk()

calc = Frame(root)

calc.grid()

root.title("Calculator")

text_box = Entry(calc, justify=RIGHT)

text_box.grid(row = 0, column = 0, columnspan = 3, pady = 5)

text_box.insert(0, "0")

numbers = "789456123"

i = 0

bttn = []

for j in range(1,4):

for k in range(3):

bttn.append(Button(calc, text = numbers[i]))

bttn[i].grid(row = j, column = k, pady = 5)

bttn[i]["command"] = lambda x = numbers[i]: sum1.num_press(x)

i += 1

bttn_0 = Button(calc, text = "0")

bttn_0["command"] = lambda: sum1.num_press(0)

bttn_0.grid(row = 4, column = 1, pady = 5)

bttn_div = Button(calc, text = chr(247))

bttn_div["command"] = lambda: sum1.operation("divide")

bttn_div.grid(row = 1, column = 3, pady = 5)

bttn_mult = Button(calc, text = "x")

bttn_mult["command"] = lambda: sum1.operation("times")

bttn_mult.grid(row = 2, column = 3, pady = 5)

minus = Button(calc, text = "-")

minus["command"] = lambda: sum1.operation("minus")

minus.grid(row = 3, column = 3, pady = 5)

point = Button(calc, text = ".")

point["command"] = lambda: sum1.num_press(".")

point.grid(row = 4, column = 0, pady = 5)

add = Button(calc, text = "+")

add["command"] = lambda: sum1.operation("add")

add.grid(row = 4, column = 3, pady = 5)

neg= Button(calc, text = "+/-")

neg["command"] = sum1.sign

neg.grid(row = 5, column = 0, pady = 5)

clear = Button(calc, text = "C")

clear["command"] = sum1.cancel

clear.grid(row = 5, column = 1, pady = 5)

all_clear = Button(calc, text = "AC")

all_clear["command"] = sum1.all_cancel

all_clear.grid(row = 5, column = 2, pady = 5)

equals = Button(calc, text = "=")

equals["command"] = sum1.calc_total

equals.grid(row = 5, column = 3, pady = 5)

root.mainloop()

Recommended for you: Get network issues from **WhatsUp Gold**. **Not end users.**

Answer Source

Using a variable class is very handy for your situation because it will allow you to update the text of text_box using by setting the content of this variable. Note that doing so, you will not have to change anything else in your code apart from what I mention below:

```
var = StringVar() # Add this line
text_box = Entry(calc, justify=RIGHT, textvariable=var) # Modification here
text_box.grid(row = 0, column = 0, columnspan = 3, pady = 5)
var.set(0) # When you lunch the GUI, you will get 0 in text_box
#text_box.insert(0, "0") <-- You do not need this line
```

Now you will need to change the code `cancel()`

as follows:

```
def cancel(self):
global var
self.eq = False
self.current = self.current[:-1] # Remove last digit
if self.current: # If there is at list one digit
var.set(self.current)
else: # In this case display 0 in text_box
var.set(0)
self.new_num = True
```

Unlike what other answers mentioned, you will need to remove `self.display(0)`

in `cancel()`

.

**Demo:**

Let us type 123 and remove all the digits one by one:

Remove 3:

Remove 2:

Remove 1 (and here is where the `if ... else`

condition above is useful):

Recommended from our users: **Dynamic Network Monitoring from WhatsUp Gold from IPSwitch**. ** Free Download**