Python: 我的 except 子句真的太宽泛了吗？

Question

我的代码运行良好，但 PyCharm 警告以下 except 子句过于宽泛。老实说，它在我看来也是错误的实现。

当批量抓取 HTML<tr>s 时，我还必须将其添加到数据库或更新，我事先不知道游戏是否完成。此外，尚未完成的游戏在某些 <td> 中有不同的 HTML 标签，需要不同的处理方式。

基本上，如果我们查看 match_score_string 和 match_relevant_bit，我们就是在告诉 BeautifulSoup 找到具有特定 class 的 <td>。如果游戏已经结束，这个 <td> 会有一个 score-time sc class，如果没有，它会有一个 score-time st class。如果它有一个，它不会有另一个。

我写 try-except 子句已经有一段时间了，但如果我没记错的话，（我觉得）我必须使用它们的原因是因为当 row.find 无法找到 HTML 对象。

PyCharm抱怨有道理吗？

# Get Match Score
try:
    match_score_string = row.find("td", class_="score-time sc").get_text()
    match_string_split = match_score_string.split(" - ")
    team_a_score = int(match_string_split[0])
    team_b_score = int(match_string_split[1])
    print(team_a_score)
    print(team_b_score)
except:
    team_a_score = None
    team_b_score = None

# Get Match URL
try:
   match_relevant_bit = row.find("td", class_="score-time sc")
   match_url = match_relevant_bit.find("a").get("href")
   match_url_done = match_url.rsplit('?JKLMN')
   match_url = match_url_done[0]
   match_finished = True

except:

   match_relevant_bit = row.find("td", class_="score-time st")
   match_url = match_relevant_bit.find("a").get("href")
   match_url_done = match_url.rsplit('?JKLMN')
   match_url = match_url_done[0]
   match_finished = False

Answer 1

您的 except 确实太宽泛了。我不会质疑在这些情况下您是否需要异常处理——异常是非常 pythonic 的，所以在您认为合适的地方使用它们。但是，您没有争辩说您需要您的代码来处理每个可以想象的异常。一个 bare except 可以掩盖各种错误。例如如果您在以后的修订版中拼错了变量名：

try:
    match_score_string = row.find("td", class_="score-time sc").get_text()
    match_string_split = match_score_string.split(" - ")
    team_a_score = int(match_string_spilt[0])  # oops
    team_b_score = int(match_string_split[1])
    print(team_a_score)
    print(team_b_score)
except:
    team_a_score = None
    team_b_score = None

Bare excepts 还会阻止用户发送 KeyboardInterrupt 来终止程序...

这只是两个例子，为什么你不想要一个简单的 except -- 由于可能被它掩盖的编程错误的数量几乎是无限的，我没有足够的时间来演示所有这些错误； -).

相反，您应该准确指定您预计会遇到的异常情况：

try:
    match_score_string = row.find("td", class_="score-time sc").get_text()
    match_string_split = match_score_string.split(" - ")
    team_a_score = int(match_string_spilt[0])  # oops
    team_b_score = int(match_string_split[1])
    print(team_a_score)
    print(team_b_score)
except AttributeError:  # If no row is found, accessing get_text fails.
    team_a_score = None
    team_b_score = None

这样，代码会按您预期的方式执行并且您不会掩盖（太多）编程错误。为了防止隐藏错误，您接下来要做的是尽可能限制异常处理程序中的代码量。

Answer 2

Try/except 条款很棒。听起来你不太经常使用它们。

try/except 块可以帮助您避免复杂的 if 语句，或者在继续之前检查条件的代码，这有时会使您不清楚 trying to做（看看我在那里做了什么 :P）。

您可能会从代码中拖出一些异常，其中一些可能比其他的更有可能。见下文：

try:
    # This first line could have an AttributeError in two places
    #     Maybe the row didn't parse quite correctly? find() won't work then.
    #     Maybe you didn't find any elements? get_text() won't work then.
    match_score_string = row.find("td", class_="score-time sc").get_text()
                            ^                                  ^
    # Same as here, you could get an AttributeError if match_score_string isn't a string.
    #     I would say that isn't very likely in this case,
    #     Especially if you handle the above line safely.
    match_string_split = match_score_string.split(" - ")

    # If either of these split strings contains no matches, you'll get an IndexError
    # If either of the strings at the index contain letters, you may get a ValueError
    team_a_score = int(match_string_split[0])
    team_b_score = int(match_string_split[1])

    # Theoretically, if you caught the exception from the above two lines
    #     you might get a NameError here, if the variables above never ended up being defined.
    print(team_a_score)
    print(team_b_score)
except:
    # Can't really imagine much going wrong here though.
    team_a_score = None
    team_b_score = None

如您所想，捕获几种类型的异常可能更有用。这取决于您输入的复杂程度。

多个 try/except 块在这里也有好处，特别是处理您发现错误并需要继续执行该块内其余代码的情况。

Python: 我的 except 子句真的太宽泛了吗？

Python: Is my except clause indeed too broad?

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