如何減少if陳述句Python？

我有一個假期日期的 df，我正在嘗試在假期前六周列出日期以添加到 df 中。共有三個串列 PreList（前一天）、MiddleList（休息日）和 PostList（后一天）。我正在使用 datetime.timedelta 來獲取假期前的六周，但我不喜歡所有的 if 陳述句。如何減少 if 陳述句？

PreList = []
DuringList = []
PostList = []

for i in range(len(df)):
    
    #for Mon
    if df.date[i].weekday() == 0:
        preDay = df.date[i] - datetime.timedelta(days = 3)
        preWeek = preDay - datetime.timedelta(weeks = 6)
        during = df.date[i]
        postDay = df.date[i]   datetime.timedelta(days = 1)
        postWeek = postDay - datetime.timedelta(weeks = 6)
        PreList.append(preWeek)
        DuringList.append(during)
        PostList.append(postWeek)
        
    #for Fri
    elif df.date[i].weekday() == 4:
        preDay = df.date[i] - datetime.timedelta(days = 1)
        preWeek = preDay - datetime.timedelta(weeks = 6)
        during = df.date[i]
        postDay = df.date[i]   datetime.timedelta(days = 3)
        postWeek = postDay - datetime.timedelta(weeks = 6)
        PreList.append(preWeek)
        DuringList.append(during)
        PostList.append(postWeek)
        
    #for Sat
    elif df.date[i].weekday() == 5:
        pre = df.date[i] - datetime.timedelta(days = 1)
        preWeek = preDay - datetime.timedelta(weeks = 6)
        during = df.date[i]
        postDay = df.date[i]   datetime.timedelta(days = 2)
        postWeek = postDay - datetime.timedelta(weeks = 6)
        PreList.append(preWeek)
        DuringList.append(during)
        PostList.append(postWeek)
        
    #for Sun
    elif df.date[i].weekday() == 6:
        preDay = df.date[i] - datetime.timedelta(days = 2)
        preWeek = preDay - datetime.timedelta(weeks = 6)
        during = df.date[i]
        postDay = df.date[i]   datetime.timedelta(days = 1)
        postWeek = postDay   datetime.timedelta(weeks = 6)
        PreList.append(preWeek)
        DuringList.append(during)
        PostList.append(postWeek)
        
    #for Tue - Thu
    else:
        preDay = df.date[i] - datetime.timedelta(days = 1)
        preWeek = preDay - datetime.timedelta(weeks = 6)
        during = df.date[i]
        postDay = df.date[i]   datetime.timedelta(days = 1)
        postWeek = postDay   datetime.timedelta(weeks = 6)
        PreList.append(preWeek)
        DuringList.append(during)
        PostList.append(postWeek)

uj5u.com熱心網友回復：

您可以使用 adict來保存引數。

PreList = []
DuringList = []
PostList = []

params_map = {0: [3, 6, 1, 6],
              1: [1, 6, 1, 6],
              2: [1, 6, 1, 6],
              3: [1, 6, 1, 6],
              4: [1, 6, 3, 6],
              5: [1, 6, 2, 6],
              6: [2, 6, 1, 6]}

for i in range(len(df)):
    key = df.date[i].weekday()
    params = params_map[key]

    preDay = df.date[i] - datetime.timedelta(days=params[0])
    preWeek = preDay - datetime.timedelta(weeks=params[1])
    during = df.date[i]
    postDay = df.date[i]   datetime.timedelta(days=params[2])
    postWeek = postDay - datetime.timedelta(weeks=params[3])
    PreList.append(preWeek)
    DuringList.append(during)
    PostList.append(postWeek)

uj5u.com熱心網友回復：

我個人會使用一行 if 陳述句，然后用代碼呼叫一個函式。這種方式更簡潔，if 陳述句使用更少的代碼。

weekday5() if df.date[i].weekday() == 5 

這些每個占用一行代碼，并呼叫一個函式。這是我知道的最簡單的方法。

uj5u.com熱心網友回復：

我會創建一個時間增量的字典（或更簡單的串列，因為索引從 0-6 開始），這樣您就可以通過簡單的查找生成“前/后”條目：

PreList = []
DuringList = []
PostList = []

pre_post = [
    # Pre/post day offsets by weekday.
    (3, 1),      # Mon
    (43, 43),    # Tue
    (43, 43),    # Wed
    (43, 43),    # Thu
    (1, 3),      # Fri
    (1, 2),      # Sat
    (44, 43),    # Sun
]

for i in range(len(df)):
    d = df.date[i]
    pre, post = pre_post[d.weekday()]
    PreList.append(d - datetime.timedelta(days=pre))
    DuringList.append(d)
    PostList.append(d   datetime.timedelta(days=post))

這不僅減少了if陳述句的數量和整體代碼的數量，而且可以很容易地在一個地方一目了然地查看每天的偏移量（并在需要時更新），而不必滾動瀏覽一堆其他代碼。

標籤：Python 列表 数据框 if 语句

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