英文:
Nested 'if else' functions
问题
以下是翻译好的部分：
让我们假设我们需要下载一个文件，检查一个值是否为True，如果是的话，我们需要通过电子邮件通知管理员。
我想把所有不同的任务分成易于管理的步骤（函数）。然后逐个调用每个函数。
这创建了以下函数：
def alert_admin():
if download_file() == True: # 文件已下载，检查文件是否存在
if extract_file() == True: # 压缩文件包含正确的文件
if read_file() == True: # 读取文件并检查值是否存在
if value_in_file() == True:
# 发送管理员电子邮件
pass
else:
pass
else:
pass
else:
pass
else:
pass
这个方法感觉不太对，有没有更好的方法（更符合Python风格）来检查某些函数的结果并继续下一个步骤？
英文:
Let's say we have to download a file, check if a value is True and if so, we need to alert the admin by email.
I would like to split up all the different things to do in easy to manage steps (functions). And then call each function one by one.
This create the following function:
def alert_admin():
if download_file() == True: # File is downloaded, check if file is present
if extract_file() == True: # Zip file contains the correct file
if read_file() == True: # Read the file and the value is there
if value_in_file() == True:
# send the admin an email
pass
else:
pass
else:
pass
else:
pass
else:
pass
This just doesn't feel right, is there a better way (a more pythonic) to check the outcome of certain functions and proceed to the next?
答案1
得分: 9
以下是翻译好的部分：
第一种方法：早期返回模式
你有几种避免深度嵌套控制流的选择。一个常见的方法是"早期返回模式" - 简单地测试下一步是否失败，如果失败就立即返回：
def alert_admin():
if not download_file():
return
if not extract_file():
return
if not read_file():
return
if not value_in_file():
return
# 在这里发送电子邮件
第二种方法：短路评估
另一种选择是短路评估。你可以使用and布尔运算符连接函数调用 - 如果左操作数返回false，运算符将跳过评估右操作数，从而确保"早期返回"：
def alert_admin():
if download_file() and extract_file() and read_file() and value_in_file():
# 在这里发送电子邮件
第三种方法：使用列表迭代
最后，由于所有函数调用具有相同的签名，你还可以将"步骤"存储在一个列表中并对其进行迭代 - 这可能会使维护更容易，因为你只需向列表中添加或删除函数名称以更新行为：
def alert_admin():
required_steps = [
download_file,
extract_file,
read_file,
value_in_file
]
for step in required_steps:
if not step():
return
# 在这里发送电子邮件
英文:
You have a couple of options for avoiding deeply nested control flows. A popular approach is the "return early pattern" - simply test whether the next step fails, then return immediately if it does:
def alert_admin():
if not download_file():
return
if not extract_file():
return
if not read_file():
return
if not value_in_file():
return
# send email here
Another option is short-circuiting. You chain the function calls with the and boolean operator - if the left-hand operand returns false the operator will skip evaluating the right-hand operand, thus ensuring "early return" as well:
def alert_admin():
if download_file() and extract_file() and read_file() and value_in_file():
# send email here
Finally, since the function calls all have the same signature, you can also store the "steps" in a list and iterate over that - this might make maintenance easier as you can simply add or remove function names to/from the list to update the behavior:
def alert_admin():
required_steps = [
download_file
extract_file
read_file
value_in_file
]
for step in required_steps:
if not step():
return
# send email here
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