勾股跳出回路

Question

这里完全是蟒蛇初学者。

我有以下函数，它检查从某些输入派生出来的字符串是否存在于文本文件中。它循环遍历文本文件的每一行，以查看是否找到了确切的匹配。

在发现比赛后，我必须立即挣脱圈套，以避免不必要的循环。

以下是代码：

def DateZoneCity_downloaded_previously(Order_Date,ZoneCity):    #   function to check if a given DateZoneCity
                                                                    #   combination had already been completely downloaded
    string_to_match = Order_Date.strftime('%Y/%m/%d') + "-" + ZoneCity[0] + "-" + ZoneCity[1]
    with open(Record_File) as download_status:
        DateZoneCity_exists = False
        for line in download_status:
            if string_to_match in line:
                DateZoneCity_exists = True                      #   if match found, then set "DateZoneCity_exists" to True
                break                                           #   and break out from the [for line in download_status:] loop
        if DateZoneCity_exists: return True
    download_status.close()

我正在寻找一种更简洁的、节奏式的方法来构造代码。我能做些什么让这件事变得更好吗？以某种方式消除了对"DateZoneCity_exists“和第二个If语句的需求？

Answer 1

在这种情况下，any是最好的解决方案：

# Function to check if a given DateZoneCity
def DateZoneCity_downloaded_previously(Order_Date, ZoneCity):
    # Combination had already been completely downloaded
    string_to_match = Order_Date.strftime('%Y/%m/%d') + "-" + ZoneCity[0]
                                                      + "-" + ZoneCity[1]
    with open(Record_File) as download_status:
        return any((string_to_match in line) for line in download_status)

请注意，在这种情况下，它将返回负的False，而不是返回None的当前实现，还请注意，它在找到正结果时确实会跳出循环，因此它不需要以任何方式循环整个文件。

Answer 2

只是return而不是break

def DateZoneCity_downloaded_previously(Order_Date,ZoneCity):
    """Check if a given DataZoneCity combination had already been downloaded."""
    string_to_match = Order_Date.strftime('%Y/%m/%d') + "-" + ZoneCity[0] + "-" + ZoneCity[1]
    with open(Record_File) as download_status:
        for line in download_status:
            if string_to_match in line:
                return True
    return False  # No match found.

Answer 3

根据文本文件的大小，您可以将其读入字符串，只需使用它(比每行读取和检查行更容易，而且速度更快)：

if string_to_match in open(Record_File).read():
    return True

在你的例子中：

def DateZoneCity_downloaded_previously(Order_Date,ZoneCity):                   
    string_to_match = Order_Date.strftime('%Y/%m/%d') + "-" + ZoneCity[0] + "-" + ZoneCity[1]
    if string_to_match in open(Record_File).read():
        return True