import datetime as dt
import matplotlib.pyplot as plt
import matplotlib.font_manager as font_manager
import matplotlib.dates as dates
from matplotlib.dates import WEEKLY, MONTHLY, DateFormatter, rrulewrapper, RRuleLocator
import numpy as np
from tkinter import *

def create_date(date):
    d, m, y = [int(s) for s in date.split('-')]
    return dates.date2num(dt.datetime(y, m, d))

def create_diagramm_gantt(event):
    name_characters, custom_dates = [],[]
    for people in characters: name_characters.append(people["Name"]); custom_dates.append([create_date(people["Begin_date"]),create_date(people["End_date"])])
    number_characters = len(name_characters)
    position, date_of_task = np.arange(0.5,number_characters*0.5+0.5,0.5),{}
    for i, name in enumerate(name_characters): date_of_task[name] = custom_dates[i]
    figure = plt.figure(figsize=(20,8))
    ax = figure.add_subplot(111)
    for i in range(number_characters):
        start_date,end_date = date_of_task[name_characters[i]]
        ax.barh((i*0.5)+0.5, end_date - start_date, left=start_date, height=0.3, align='center', edgecolor='lightgreen', color='lightgreen', alpha = 0.8)
    _, labelsy = plt.yticks(position,name_characters)
    plt.setp(labelsy, fontsize = 14)
    ax.set_ylim(ymin = -0.1, ymax = number_characters*0.5+0.5)
    ax.grid(color = 'g', linestyle = ':')
    ax.xaxis_date()
    location = RRuleLocator(rrulewrapper(WEEKLY, interval=1))
    formatter = DateFormatter("%d-%b '%y")
    ax.xaxis.set_major_locator(location)
    ax.xaxis.set_major_formatter(formatter)
    plt.setp(ax.get_xticklabels(), rotation=30, fontsize=10)
    font = font_manager.FontProperties(size='small')
https://pastebin.com/BQtrqNkn