def calculate_GP(GP_1,GP_2):
    
        diff_1=GP_1+1
        diff_2=GP_2+1
        return diff_1, diff_2
 
current_GP={}
for idx,row in df.iterrows():
    
    Player_1=row['Player1']
    Player_2=row['Player2']
    
    if Player_1 not in current_GP.keys():
        current_GP[Player_1]=0
    
    if Player_2 not in current_GP.keys():
        current_GP[Player_2]=0
        
    GP_1=current_GP[Player_1]
    GP_2=current_GP[Player_2]
    
    diff_1,diff_2=calculate_GP(GP_1,GP_2)
    
    current_GP[Player_1]=diff_1
    current_GP[Player_2]=diff_2
    
    df.loc[idx,'GP1']=GP_1
    df.loc[idx,'GP2']=GP_2

  
import datetime
import pandas as pd
df = pd.read_csv('/home/xam/Загрузки/Tennis_2010.csv')
def count_games_player(df, player, date_start, date_end):
    """
    
    :param df: таблица
    :param player: имя игрока
    :param date_start: начальная дата откуда считать
    :param date_end: конечная дата (не входит в счет)
    :return: количество игр
    """
    def my_filter(value):
        date = datetime.datetime.strptime(value['Date'], '%m/%d/%Y').date()
        return datetime.date(*date_start) <= date < datetime.date(*date_end) \
               and (value['Player1'] == player or value['Player2'] == player)
    out_df = df[df.apply(lambda x: my_filter(x), axis=1)]
    return len(out_df)
 
if __name__ == '__main__':
    res = count_games_player(df, 'Rafael Nadal', (2010, 1, 2), (2010, 12, 31))
    print(res)
    res2 = count_games_player(df, 'Rafael Nadal', (2010, 1, 2), (2010, 3, 31))
    print(res2)

 
80
17

Process finished with exit code 0

 if __name__ == '__main__':