相关疑难解决方法(0)

在Python中,可以使用单行来以简单,直观的方式设置具有特殊条件(例如默认值或条件)的值.

result = 0 or "Does not exist."  # "Does not exist."

result = "Found user!" if user in user_list else "User not found."

是否有可能编写一个捕获异常的类似语句？

from json import loads

result = loads('{"value": true}') or "Oh no, explosions occurred!"
# {'value': True}

result = loads(None) or "Oh no, explosions occurred!"
# "Oh no, explosions occurred!" is desired, but a TypeError is raised.

我有一个代码,我尝试访问资源,但有时它不可用,并导致异常.我尝试使用上下文管理器实现重试引擎,但我无法处理__enter__上下文表单上下文管理器中调用者引发的异常.

class retry(object):
    def __init__(self, retries=0):
        self.retries = retries
        self.attempts = 0
    def __enter__(self):
        for _ in range(self.retries):
            try:
                self.attempts += 1
                return self
            except Exception as e:
                err = e
    def __exit__(self, exc_type, exc_val, traceback):
        print 'Attempts', self.attempts

这是一些只引发异常的例子(我希望处理的那个)

>>> with retry(retries=3):
...     print ok
... 
Attempts 1
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
NameError: name 'ok' is not defined
>>> 
>>> with retry(retries=3):
...     open('/file')
... 
Attempts 1
Traceback …

我是Python的新手，仍然在学习技巧。

我如何将以下代码转换为单个内衬，在Python中可以吗？必须有一种整齐的方法来做到这一点。

try:
    image_file = self.request.files['image_path']
except:
    image_file = None