Python try-except 块的 DRY 方法？

Question

Objective: 我有几行代码，每行代码都会产生相同类型的错误，并保证相同类型的响应。如何防止 try-except 块出现 'do not repeat yourself' 问题。

背景：

我使用 ReGex 从文本文件中抓取格式不正确的数据，并将其输入到自定义对象的字段中。该代码工作得很好，除非该字段留空，在这种情况下它会抛出错误。

我在 try-except 块中处理这个错误。如果错误，则在对象的字段中插入一个空格（即“”）。

问题是它将易读、漂亮、Python 代码变成了一堆 try-except 块，每个块都做完全相同的事情。这是 'do not repeat yourself'（a.k.a。干燥）违规行为。

代码：

之前:

sample.thickness = find_field('Thickness', sample_datum)[0]
sample.max_tension = find_field('Maximum Load', sample_datum)[0]
sample.max_length = find_field('Maximum Extension', sample_datum)[0]
sample.test_type = sample_test

之后：

try:
    sample.thickness = find_field('Thickness', sample_datum)[0]
except:
    sample.thickness = ''

try:
    sample.max_tension = find_field('Maximum Load', sample_datum)[0]
except:
    sample.max_tension = ''

try:
    sample.max_length = find_field('Maximum Extension', sample_datum)[0]
except: 
    sample.max_length = ''

try:    
    sample.test_type = sample_test
except:
    sample.test_type = ''

我需要什么：

有什么 Pythonic 的写法吗？在某些块中，如果这些行中的任何一行出现索引超出范围错误（表明该字段为空白，并且 ReGex 无法 return 任何内容），我可以在示例字段中插入一个空白。

Answer 1

您可以反复使用任意数量的 except 块，处理不同类型的异常。在同一个 try/catch 块中有多个语句也没有错。

try:
    doMyDangerousThing()
except ValueError:
    print "ValueError!"
except HurrDurrError:
    print "hurr durr, there's an error"

try:
    doMyDangerousThing()
    doMySecondDangerousThing()
except:
    print "Something went wrong!"

Answer 2

从中提取一个函数怎么样？

def maybe_find_field(name, datum):
    try:
        return find_field(name, datum)[0]
    except IndexError: # Example of specific exception to catch
        return ''

sample.thickness = maybe_find_field('Thickness', sample_datum)
sample.max_tension = maybe_find_field('Maximum Load', sample_datum)
sample.max_length = maybe_find_field('Maximum Extension', sample_datum)
sample.test_type = sample_test

顺便说一句，不要简单地使用 except: 捕获所有可能的异常，除非这确实是您想要做的。捕获所有内容可能会隐藏实现错误，并且以后很难调试。只要有可能，将您的 except 案例绑定到您需要的特定异常。

Answer 3

当你发现自己在重复代码时，将其封装在一个函数中。在这种情况下，创建一个函数来为您处理异常。

def try_find_field(field_name, datum, default_value):
    try:
        return find_field(field_name, datum)[0]
    except:
        return default_value

Answer 4

像这样的事情怎么样：

def exception_handler(exception_class):
    logger = logging.getLogger('app_error')
    logger.error(exception_class)

    exception_name = exception_class.__name__

    if exception_name == 'AuthenticationError':
        raise AuthenticationError
    elif exception_name == 'AuthorizationError':
        raise AuthorizationError
    elif exception_name == 'ConnectionError':
        raise ConnectionError
    else:
        raise GenericError

def call_external_api()
    try:
        result = http_request()
    except Exception as e:
        exception_handler(exception_class=type(e))

Answer 5

不太符合问题，但是 Google 派我来这里，所以其他人可能会来。

我在两个单独的 Django 视图中有 post 函数，它们调用相似的后端函数并需要相同的异常处理。

我通过提取整个 except:-tree 并将其粘贴到装饰器中解决了这个问题。

之前：

# twice this
def post(request):
    try:
        return backend_function(request.post)
    except ProblemA as e:
        return Response("Problem A has occurred, try this to fix it.", status=400)
    except ProblemB as e:
        return Response("Problem B has occurred, try this to fix it.", status=400)
    except ProblemC as e:
        return Response("Problem C has occurred, try this to fix it.", status=400)
    except ProblemD as e:
        return Response("Problem D has occurred, try this to fix it.", status=400)

之后：

# once this
def catch_all_those_pesky_exceptions(original_function):
    def decorated(*args, **kwargs):
        try:
            return original_function(*args, **kwargs)
        except ProblemA as e:
            return Response("Problem A has occurred, try this to fix it.", status=400)
        except ProblemB as e:
            return Response("Problem B has occurred, try this to fix it.", status=400)
        except ProblemC as e:
            return Response("Problem C has occurred, try this to fix it.", status=400)
        except ProblemD as e:
            return Response("Problem D has occurred, try this to fix it.", status=400)

    return decorated

# twice this - note the @decorator matching the above function.
@catch_all_those_pesky_exceptions
def post(request):
    return backend_function(request.post)

现在我可以在一个地方添加更多的异常处理。

Python try-except 块的 DRY 方法？

A DRY approach to Python try-except blocks?

python

python-2.7

try-except