Pythonのcalendarを再現

import calendar
year = 2021
month = 7
text0 = calendar.month(year, month)
print(text0)

import calendar
year = 2021
month = 7
calendar.setfirstweekday(calendar.SUNDAY)
text0 = calendar.month(year, month)
print(text0)

def calendar_month(year, month, sunday_start = False):
  # 月のカレンダーを文字列で返す。
  # デフォルトは月曜日始まり
  first_date = datetime.date(year, month, 1)
  first_yobi = first_date.weekday() # 0:月 6:日
  if sunday_start == False:
    first_yobi -= 1
  if first_yobi == 6:
    first_yobi = - 1
  if month == 12:
    temp_year = year + 1
    temp_month = 1
  else:
    temp_year = year
    temp_month = month
  last_date = datetime.date(temp_year, temp_month + 1, 1) - datetime.timedelta(days = 1)
  last_day = last_date.day
  num_day = first_yobi + last_day + 1
  first_sunday = first_date - datetime.timedelta(first_yobi)
  num_week = math.ceil(num_day / 7)
  lines = []
  title = first_date.strftime("%B %Y") # 月(英語) 年
  lines.append(title.center(20, " ")) # 中央揃え
  if sunday_start:
    lines.append("Su Mo Tu We Th Fr Sa")
  else:
    lines.append("Mo Tu We Th Fr Sa Su")
  for r in range(num_week):
    parts = []
    for c in range(7):
      dateobj = first_sunday + datetime.timedelta(days = r * 7 + c - 1)
      if dateobj.month == month:
        this_day = str(dateobj.day).rjust(2)
      else:
        this_day = "  "
      parts.append(this_day)
    lines.append(" ".join(parts))
  text = "\n".join(lines)
  return text

import datetime
import math

year = 2024
month = 5

# 月曜日始まり
text1 = calendar_month(year, month)
print(text1)

# 日曜日始まり
text1 = calendar_month(year, month, True)
print(text1)