python - 如何忽略无效输入或在排序函数中添加 try except 代码？

Question

我想根据日期对字典列表进行排序。

以下代码在我的数据格式固定的情况下工作正常，即 dd/mm/yyyy

代码:

[{'date': '10/10/2015'},
 {'date': '11/10/2015'},
 {'date': '01/01/2015'},
 {'date': '10/12/2014'},
 {'date': '01/01/2014'},
 {'date': '2015'}]

In [20]: a.pop()
Out[20]: {'date': '2015'}

In [21]: sorted(a, key=lambda x: datetime.datetime.strptime(x['date'], "%d/%m/%Y"), reverse=False)
Out[21]: 
[{'date': '01/01/2014'},
 {'date': '10/12/2014'},
 {'date': '01/01/2015'},
 {'date': '10/10/2015'},
 {'date': '11/10/2015'}]

但我也有与 dd/mm/yyyy 格式不匹配的日期值。获取以下异常:

代码2:

In [22]: a.append({"date":"2015"})

In [23]: sorted(a, key=lambda x: datetime.datetime.strptime(x['date'], "%d/%m/%Y"), reverse=False)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-23-abd07eed54eb> in <module>()
----> 1 sorted(a, key=lambda x: datetime.datetime.strptime(x['date'], "%d/%m/%Y"), reverse=False)

<ipython-input-23-abd07eed54eb> in <lambda>(x)
----> 1 sorted(a, key=lambda x: datetime.datetime.strptime(x['date'], "%d/%m/%Y"), reverse=False)

/usr/lib/python2.7/_strptime.py in _strptime(data_string, format)
    323     if not found:
    324         raise ValueError("time data %r does not match format %r" %
--> 325                          (data_string, format))
    326     if len(data_string) != found.end():
    327         raise ValueError("unconverted data remains: %s" %

ValueError: time data '2015' does not match format '%d/%m/%Y'

In [24]: 

如何在 sorted 函数中处理此类输入？？

Answer 1

一个选项是在关键函数中处理异常:

def custom_sort(x):
    try:
        return datetime.datetime.strptime(x['date'], "%d/%m/%Y")
    except ValueError:
        # do something else if the date format is different
    except KeyError:
        # do something else if there is no 'date' key in x
        # ...

sorted(a, key=custom_sort)

或者您可以使用 if-else 结构在应用日期时间函数之前将数据转换为正确的格式...

---

编辑:这里有两个更实用的选项:

a = [{'date': '05/06/2017'}, {'ff': 2016}, {'date': 2015}, {'date': '05/06/2014'}, 'ff']

def sort_by_converting_to_strings(x):
    try:
        return str(datetime.datetime.strptime(x['date'], "%d/%m/%Y"))
    except (KeyError, ValueError, TypeError):
        try:
            return str(x['date'])
        except (KeyError, TypeError):
                return str(x)
print sorted(a, key=sort_by_converting_to_strings)
# [{'date': '05/06/2014'}, {'date': 2015}, {'date': '05/06/2017'}, 'ff', {'ff': 2016}]


def validate(x):
    try:
        datetime.datetime.strptime(x['date'], "%d/%m/%Y")
        return True
    except Exception:
        return False
print sorted([i for i in a if validate(i)])
# [{'date': '05/06/2014'}, {'date': '05/06/2017'}]

当然，您可以结合这些方法来获得适合您特定用例的解决方案...