from tkinter import *
import re
def c10to2(x):
    if x == '0': return '0'
    if re.match(r'\d+\b',x):
        s = ''
        x = int(x)
        while x >=1:
            s+=str(x%2)
            x//=2
        return s[::-1]
    else:
        return 'ERROR'
def c2to10(x):
    if re.match(r'[01]+\b',x):
        x = str(x)
        y = 0
        n = len(x)-1
        for i in x:
            y+=int(i)*(2**n)
            n-=1
        return y
    return 'ERROR'
def c10to16(x):
    d = {10:'A',11:'B',12:'C',
         13:'D',14:'E',15:'F'}
    s = ''
    x = int(x)
    while x >= 1:
        if x%16 > 9:
            s+= d.get(x%16)
        else:
            s+=str(x%16)
        x//=16
    return s[::-1]
def c16to10(x):
    d = {'A':10,'B':11,'C':12,
         'D':13,'E':14,'F':15}
    x = x.upper()
    if re.match(r'[0-9A-F]+\b',x):
        n = len(x)-1
        y = 0
        for elem in x:
            if elem.isdigit():
                y+=int(elem)*(16**n)
            else:
                y+= d.get(elem)*(16**n)
            n-=1
        return y
    else: return 'ERROR'
def c10to8(x):
    if re.match(r'\d+\b',x):
        s = ''
        x = int(x)
        while x >=1:
            s+=str(x%8)
            x//=8
        return s[::-1]
    else: return 'ERROR'
def c8to10(x):
    x = str(x)
    if re.match(r'[0-7]+\b',x):
        n = len(x)-1
        y = 0
        for elem in x:
            y+=int(elem)*(8**n)
            n-=1
        return y
    else: return 'ERROR'

def etake(e):
    number = my_number.get()
    x = qwe.get()
    y = rty.get()
    if x == 10 and y == 2:
        my_solve.delete(0,END)
        my_solve.insert(END,c10to2(number))
    elif x == 2 and y == 10:
        my_solve.delete(0,END)
        my_solve.insert(END,c2to10(number))
    elif x == 2 and y == 8:
        my_solve.delete(0,END)
        my_solve.insert(END,c10to8(str(c2to10(number))))
    elif x == 2 and y == 16:
        my_solve.delete(0,END)
        my_solve.insert(END,c10to16(str(c2to10(number))))
    elif x == 10 and y == 16:
        my_solve.delete(0,END)
        my_solve.insert(END, c10to16(number))
    elif x == 8 and y == 2:
        my_solve.delete(0,END)
        my_solve.insert(END, c10to2(str(c8to10(number))))
    elif x == 8 and y == 16:
        my_solve.delete(0,END)
        my_solve.insert(END, c10to16(str(c8to10(number))))
    elif x == 16 and y == 2:
        my_solve.delete(0,END)
        my_solve.insert(END, c10to2(str(c16to10(number))))
    elif x == 16 and y == 8:
        my_solve.delete(0,END)
        my_solve.insert(END, c10to8(str(c16to10(number))))
    elif x == 16 and y == 10:
        my_solve.delete(0,END)
        my_solve.insert(END, c16to10(number))
    elif x == 10 and y == 8:
        my_solve.delete(0,END)
        my_solve.insert(END, c10to8(number))
    elif x == 8 and y == 10:
        my_solve.delete(0,END)
        my_solve.insert(END, c8to10(number))
    elif x == y:
        my_solve.delete(0,END)
        my_solve.insert(END, number)           
    else:
        return 'ERROR'
w = Tk()

w.title('Системы счисления')
w.geometry('315x145')
w.resizable(0,0)
first_text = Label(w,text='Перевести из ',font=14)
second_text = Label(w,text='в',font=14)
third_text = Label(w,text="Моё число: ",font=14)
qwe = IntVar(w)
rty = IntVar(w)
ch = [2,8,10,16]
my_sys = OptionMenu(w,qwe,*ch)
needed_sys = OptionMenu(w,rty,*ch)

my_number=Entry(w,width=20)
my_solve=Entry(w,width=20)
b = Button(w,text='Go!',bg='pink',height=2,width=5,command=lambda event='<Button-1>': etake('<Button-1>')) # Теперь результат выдаётся как по нажатию на кнопку "Go", так и...
my_number.bind('<Return>',etake) # ... по простому нажатию на Enter

first_text.place(x=6,y=10)
my_sys.place(x=130,y=10)
second_text.place(x=195,y=10)
third_text.place(x=6,y=42)
needed_sys.place(x=222,y=10)
my_number.place(x=6, y=70)
b.place(x=135,y=65)
my_solve.place(x=185,y=70)

w.mainloop()