import pymysql.cursors
from random import randint

conn = pymysql.connect(host='localhost', user='dawit', password='dw951028', db='biuro',
                       cursorclass=pymysql.cursors.DictCursor)
a = conn.cursor()
conn.autocommit(True)

sql = "SELECT COUNT(*) AS row_sum FROM biuro.osoba"
insert_sql = "UPDATE biuro.osoba SET plec = %s"

a.execute(sql)

gender_list = ["mezczyzna", "kobieta"]

for i in a:
    b = i['row_sum']

l1 = [(gender_list[randint(0,1)], i) for i in range(1,b)]
a.executemany(insert_sql, l1)