可以在一行中完成三个迭代吗？ Python 3 for 循环答案

【问题标题】：Can three iterations can be done in a single line? Python 3 for loop可以在一行中完成三个迭代吗？ Python 3 for 循环
【发布时间】：2019-07-15 07:08:08
【问题描述】：

以下代码可以正常工作。但是不是调用 player_apps 三次可以在一个语句中完成吗？

for club in all_clubs:
    total_app = sum(player['season_apps'] for player in players_apps if player['player_club'] == club)
    total_sub_app = sum(player['season_sub_apps'] for player in players_apps if player['player_club'] == club)
    total_goals = sum(player['season_goals'] for player in players_apps if player['player_club'] == club)
    club_app_goal.append({'club' : club, 'total_app' : total_app, 'total_sub_app' : total_sub_app, 'total_goals' : total_goals})

【问题讨论】：

标签： python-3.x list dictionary for-loop

【解决方案1】：

使用numpy：

for club in all_clubs:
    total_app = np.sum([[player['season_apps'], player['season_sub_apps'], player['season_goals']] for player in players_apps if player['player_club'] == club], axis=1)
    club_app_goal.append({'club' : club, 'total_app' : total_app[0], 'total_sub_app' : total_app[1], 'total_goals' : total_app[2]})

【讨论】：

【解决方案2】：

好吧，从技术上讲，使用 functools.reduce 是可以的，但它不会使代码更漂亮，而且我不确定它是否真的会提高性能：

total_app, total_sub_app, total_goals = reduce(
    lambda a, b: tuple(x + y for x, y in zip(a, b)), 
    ((p['season_apps'], p['season_sub_apps'], p['season_goals']) for p in players_apps if p["club"] == club), 
    (0, 0, 0)
    )

恕我直言，一个更有趣的“优化”是每个俱乐部只过滤一次球员：

for club in all_clubs:
    players = [player for player in players_apps if player['player_club'] == club]
    total_app = sum(player['season_apps'] for player in players)
    total_sub_app = sum(player['season_sub_apps'] for player in players)
    total_goals = sum(player['season_goals'] for player in players)

它更具可读性，甚至可能实际上更快（或不更快，取决于您的数据）。

话虽如此，您可能会受益于使用适当的关系数据库（关系数据库专为此类计算而设计）或至少 Numpy 或 Panda。

【讨论】：