Формула для вывода текста по центру ячейки

#!/usr/bin/python
 
from PIL import Image, ImageDraw, ImageFont
import datetime
 
black = (0, 0, 0)
white = (255, 255, 255)
font1 = ImageFont.truetype("Verdana.ttf", 20)
font2 = ImageFont.truetype("Verdana.ttf", 14)
 
def SaveImage(image):
    now = datetime.datetime.now()
    filename = "Timetable_" + now.strftime("%d_%m_%Y") + ".jpg"
    image.save(filename)
 
def DrawLines(draw):
 
    # Drawing vertical lines
    x = 100
    y1 = 0
    y2 = 768
 
    draw.line((x, y1, x, 370), black)
    draw.line((x, 398, x, y2), black)
 
    for n in range(0, 7):
        x += 154
        draw.line((x, y1, x, 370), black)
        draw.line((x, 398, x, y2), black)
 
 
    # Drawing horizontal lines (first week)
    y = 50
    x1 = 0
    x2 = 1024
 
    draw.line((x1, y, x2, y), black)
 
    for n in range(0, 5):
        y += 64
        draw.line((x1, y, x2, y), black)
 
    # Drawing horizontal lines (second week)
    y += 28
    draw.line((x1, y, x2, y), black)
    y += 50
    draw.line((x1, y, x2, y), black)
 
 
    for n in range(0, 5):
        y += 64
        draw.line((x1, y, x2, y), black)
 
def WriteHead(draw):
 
    # Fill first week
    text = "1 неделя"
    xy = GetXY(text, 0, 0, 100, 50)
    draw.text((xy[0], xy[1]), text, black, font=font1)
 
 
    day = ["Понедельник", "Вторник", "Среда", "Четверг", "Пятница", "Суббота"]
    for i in range(0, 6):
        xy = GetXY(day[i], 100 + 154*i, 0, 254 + 154*i, 50)
        draw.text((5 + xy[0], xy[1]), day[i], black, font=font1)
 
 
    time = ["8:30 - 10:00", "10:10 - 11:40", "12:00 - 13:30", "14:00 - 15:30", "15:40 - 17:10"]
    for i in range(0, 5):
        xy = GetXY(time[i], 0, 50 + 64*i, 100, 114 + 64*i)
        draw.text((xy[0], 74 + 64*i), time[i], black, font=font2)
 
    # Fill second week
    text = "2 неделя"
    xy = GetXY(text, 0, 398, 100, 448)
    draw.text((xy[0], 28 + xy[1]), text, black, font=font1)
 
    for i in range(0, 6):
        xy = GetXY(day[i], 100 + 154 * i, 398, 254 + 154 * i, 448)
        draw.text((5 + xy[0], 28 + xy[1]), day[i], black, font=font1)
 
    for i in range(0, 5):
        xy = GetXY(time[i], 0, 50 + 64 * i, 100, 114 + 64 * i)
        draw.text((xy[0], 472 + 64 * i), time[i], black, font=font2)
 
def WriteBody(draw):
    # Fill first week
    lines = [line.rstrip('\n') for line in open('Timetable.txt')]
    N = 0
 
    for j in range(0, 6):
        for i in range(0, 5):
            while(lines[N].find("[") == 0):
                N += 1
 
            text = lines[N].split(' ::: ')
            xy = GetXY(text[0], 100 + j*154, 50 + 64 * i, 254 + j*154, 114 + 64 * i)
            draw.text((xy[0], xy[1] - 10), text[0], black, font=font2)
            xy = GetXY(text[1], 100 + j*154, 50 + 64 * i, 254 + j*154, 114 + 64 * i)
            draw.text((xy[0], xy[1] + 5), text[1], black, font=font2)
            xy = GetXY(text[2], 100 + j*154, 50 + 64 * i, 254 + j*154, 114 + 64 * i)
            draw.text((xy[0], xy[1] + 20), text[2], black, font=font2)
            N += 1
 
 
    # Fill second week
    for j in range(0, 6):
        for i in range(0, 5):
            while (lines[N].find("[") == 0):
                N += 1
 
            text = lines[N].split(' ::: ')
            xy = GetXY(text[0], 100 + j * 154, 448 + 64 * i, 254 + j * 154, 512 + 64 * i)
            draw.text((xy[0], 20+xy[1] - 10), text[0], black, font=font2)
            xy = GetXY(text[1], 100 + j * 154, 448 + 64 * i, 254 + j * 154, 512 + 64 * i)
            draw.text((xy[0], 20+xy[1] + 5), text[1], black, font=font2)
            xy = GetXY(text[2], 100 + j * 154, 448 + 64 * i, 254 + j * 154, 512 + 64 * i)
            draw.text((xy[0], 20+xy[1] + 20), text[2], black, font=font2)
            N += 1
 
def GetXY(text, x1, y1, x2, y2):
    # Compute X-coord
    x = (x2 - x1)/2 - len(text) * 7
    if (x < 0):
        x = 0
 
    if (x2 > 100):
        x += 100
        x2 -= 100
        x2 /= 154
        for i in range(1,int(x2)):
            x += 154
 
    # Compute Y-coord
    y = (y2 - y1) / 2 - 15
 
    if (y2 > 50):
        y += 50
        y2 -= 50
        y2 /= 64
        for i in range(1,int(y2)):
            y += 64
 
    return [x, y]
 
 
def main():
    image = Image.new("RGB", (1024, 768), white)
    draw = ImageDraw.Draw(image)
    DrawLines(draw)
    WriteHead(draw)
    WriteBody(draw)
    SaveImage(image)
 
if __name__ == "__main__":
    main()

def GetXY(text, x1, y1, x2, y2):
    # Compute X-coord
    x = (x2 - x1)/2 - len(text) * 7
    if (x < 0):
        x = 0
 
    if (x2 > 100):
        x += 100
        x2 -= 100
        x2 /= 154
        for i in range(1,int(x2)):
            x += 154
 
    # Compute Y-coord
    y = (y2 - y1) / 2 - 15
 
    if (y2 > 50):
        y += 50
        y2 -= 50
        y2 /= 64
        for i in range(1,int(y2)):
            y += 64
 
    return [x, y]