New at Python programming

[Larz60+]

after you create the main window:

import tkinter as tk

root = tk.Tk()
# The set geometry
root.geometry('600x400+10+10')
root.mainloop()

the string is 'widthxheight+xoffset+yoffset'

if you are running on windows, the following class will get you screen sizes of all monitors
attached to your computer, and calculate window size based on percentage of full screen:

import sys
import screeninfo
import re


"""
GetScreenInfo()

cross platform creates a dictionary with an entry for each monitor
tied to users computer. the key is constructed as follows:
   monitor{n} n is sequentiallty assigned beginning with 1

Usage: GetScreenInfo(win_scale=.6, offset_scale=.1)
   where: scale is % of full screen, so default .6 = 60 % and
          offset is % of scaled width & height

each entry contains a nested dictionary with four values:
   swidth = scaled_width
   sheight = scaled height
   hoffset = horizontal offset
   voffset = vertical offset4

example:
>>> from GetScreenInfo import GetScreenInfo
>>> gsi = GetScreenInfo(win_scale=.8, offset_scale=.2)
>>> print(gsi.monitor_info)
>>>
    {'monitor1': {'swidth': 1920, 'sheight': 1080, 'hoffset': 384, 'voffset': 216}}

Needs testing on Apple OS-X

Author: Larz60+
"""
class GetScreenInfo:
    def __init__(self, win_scale=.6, offset_scale=.1):
        # use scale of 0 to return unmodified dimensions
        if win_scale == 0:
            newscale = 1
            newoffset = 0
        else:
            newscale = win_scale
            newoffset = offset_scale

        platform = sys.platform
        platform = platform.rstrip('1234567890')
        self.monitor_info = {}
        ostypes = {
            'linux': 'x11',
            'win': 'windows',
            'cygwin': 'cygwin',
            'darwin': 'osx'
        }

        # Following hack is for return proper linux value from sys.platform
        #  prior to python 3.3 which always starts with 'linux' but may
        #  be linux1, linux2 etc.
        if platform.startswith('linux'):
            montype = ostypes['linux']
        mon = screeninfo.get_monitors(ostypes[platform])
        # print(f'mon: {mon}')
        for n, item in enumerate(mon):
            m = re.split(r'[()x+]', str(item))
            mkey = 'monitor{}'.format(n + 1)
            self.monitor_info[mkey] = {}
            self.monitor_info[mkey]['swidth'] = int(float(m[1]) * newscale)
            self.monitor_info[mkey]['sheight'] = int(float(m[2]) * newscale)
            self.monitor_info[mkey]['hoffset'] = int(float(m[1]) * newoffset)
            self.monitor_info[mkey]['voffset'] = int(float(m[2]) * newoffset)

def main():
    gsi = GetScreenInfo(win_scale=.4, offset_scale=.2)
    print(gsi.monitor_info)

if __name__ == '__main__':
    main()

you will need the screeninfo package. you can get this with (from command line):

pip install screeninfo