Odd grid sizing behaviour - python-3.x

Question

I have been using tkinter's grid geometry manager and have configured all the rows and columns to weight = 1. The problem comes when I try to resize a Tk() window. When I resize it vertically only, the width of widgets and the proportion of column widths also change despite their equal weight. Furthermore, the width of the columns isn't in the desired proportions (i.e. all equal) before doing any resizing - to be precise the first column (with labels and buttons) is as wide as other two (holding a canvas with columnspan = 2 and two labels).
I think the problem is somehow connected to the PiSimulator._adjust_sizes function which dynamically changes the font or to the use of the canvas with a columnspan of 2.
Here's my code:
import tkinter as tk
from tkinter import font
class PiSimulator(tk.Frame):
def __init__(self, root, **kwargs):
super(PiSimulator, self).__init__(root, **kwargs)
self.root = root
self.root.title = 'Crtac krugova'
self.root.minsize(width = 600, height = 400)
self.pack(fill = 'both', expand = 1)
self.custom_font = font.Font(size = 20)
self.bind('<Configure>', self._adjust_sizes)
self.populate()
return
def populate(self):
tk.Label(self, text = 'Radijus:', font = self.custom_font, relief = 'raised',\
fg = 'green').grid(sticky='nswe', row = 0, column = 0)
self.radius = tk.IntVar()
tk.Spinbox(self, from_ = 1, to = 16, font = self.custom_font, textvariable = self.radius).grid(row = 1, column = 0)
tk.Label(self, text = 'Greška', font = self.custom_font, relief = 'raised', anchor='w',\
padx = 5, pady = 5, fg = 'green').grid(sticky='nswe', row = 0, column = 1)
self.error = tk.DoubleVar(0.0)
tk.Label(self, textvariable = self.error, font = self.custom_font, relief = 'raised',\
anchor='e', pady = 5, fg = 'green').grid(row = 0, column = 2, sticky='nswe')
self.canvas = PiCanvas(self, highlightthickness = 0)
self.canvas.grid(row = 1, rowspan = 5, column = 1, columnspan = 2, padx = 5, pady = 5, sticky='nswe')
tk.Button(self, text = 'Nacrtaj', font = self.custom_font, command = lambda: self.canvas.draw(self.radius.get())).grid(\
column = 0, row = 2, sticky='nswe')
tk.Button(self, text = 'Izbriši', font = self.custom_font, command = self.canvas.clear ).grid(\
column = 0, row = 3, sticky='nswe')
tk.Label(self, text = 'POVRŠINA', relief = 'groove', font = self.custom_font).grid(column = 0, row = 4, sticky='nswe')
self.area = tk.IntVar(0)
tk.Label(self, textvariable = self.area, relief = 'groove', font = self.custom_font).grid(column = 0, row = 5, sticky='nswe')
for i in range(3):
self.columnconfigure(i, weight = 1)
for i in range(6):
self.rowconfigure(i, weight = 1)
return
def _adjust_sizes(self, event):
new_font = int(event.height/15) - 2
self.custom_font.configure(size = new_font)
return
class PiCanvas(tk.Canvas):
def __init__(self, root, **kwargs):
super(PiCanvas, self).__init__(root, background = 'white', relief = 'groove', **kwargs)
self.root = root
self.cubes = []
self.circle = None
def draw(self, radius):
self.clear()
c_width = self.winfo_width()
c_height = self.winfo_height()
self.grid_side = int(min([c_width, c_height]))
self.grid_side-= 10
self.v_offset = (c_height - self.grid_side)/2
self.h_offset = (c_width - self.grid_side)/2
self.cube_side = self.grid_side/(2*radius)
vertix_coord = lambda x, x_cor, y_cor: x_cor*self.h_offset+y_cor*self.v_offset+x*self.cube_side
for i in range(2*radius):
new_line = []
for j in range(2*radius):
cube = self.create_rectangle(vertix_coord(i, 1, 0), vertix_coord(j, 0, 1),\
vertix_coord(i+1, 1, 0), vertix_coord(j+1, 0, 1), tag = 'unused')
new_line.append(cube)
self.cubes.append(new_line)
self.circle = self.create_oval(vertix_coord(0,1,0), vertix_coord(0,0,1),\
vertix_coord(2*radius,1,0), vertix_coord(2*radius,0,1),width = 2)
self.color_border_cubes()
print(self.circle)
def color_border_cubes(self):
circle_coords = self.coords(self.circle)
print(circle_coords)
for i in self.cubes:
for j in i:
cube_coords = self.coords(j)
if self.circle in self.find_overlapping(*cube_coords) + self.find_enclosed(*circle_coords):
self.itemconfigure(j, fill = 'green')
def clear(self):
self.cubes = []
self.circle = None
self.delete('all')
return
root = tk.Tk()
a=PiSimulator(root)
root.mainloop()