Question

所以我有一个方法，它将字典对象作为参数。我想查看字典以确保它具有所有正确的密钥，如果没有抛出自定义异常。到目前为止我的代码有效，但我想可能有更好的方法。（使用Python 2.7）

def my_method(temp_dict):
    #this is the part that looks messy and I would like to improve
    if "key" not in temp_dict:
        raise CustomException("Message key is missing from dict")
    if "key1" not in temp_dict:
        raise CustomException("Message key1 is missing from dict")
    if "key2" not in temp_dict:
        raise CustomException("Message key2 is missing from dict")
    if "key3" not in temp_dict:
        raise CustomException("Message key3 is missing from dict")

my_dict = {}
my_dict["key"] = "test"
my_dict["key1"] = "test"
my_dict["key2"] = "test"

my_method(my_dict)

链接到Python小提琴Link

Answer 1

循环可以提供帮助：

def my_method(temp_dict):
    for key in ['key1', 'key2', 'key3']
        if key not in temp_dict:
            raise CustomException("Message {} is missing from dict".format(key))

Answer 2

如何在元组中编写要检查的所有键？

def mymethod(temp_dict):
    mykeys = ('key1', 'key2', 'key3', ..., 'keyN')
    for k in mykeys:
        if k not in temp_dict:
            raise CustomException("{} missing from dictionary".format(k))

这样，只要你想添加一个新密钥来检查，你就可以将它添加到元组而不是复制代码。

Answer 3

一种可能性是使用诸如voluptuous之类的模式库，您可以在其中定义字典模式，通过定义哪些密钥是必需的，哪些是可选的，甚至是键可以接受的类型。

另一方面，如果你只需要验证是否存在所有必需的键，我就会使用这个很棒的小功能。首先，我们定义一个包含所有必需键的列表。然后我们使用all方法检查给定字典是否包含所有这些必需的键。

def validate_params(params, req_keys=[]):                                           
    """                                                                      
    Verify if all required keys are present in the dictionary passed   
    to this method                                                           

    :param params: Parameter Dictionary to check
    :param req_keys: These Keys are required in the dictionary
    :rtype: Boolean                                                          
    :returns: True or False                                                  
    """                                                                      
    if all(_ in params for _ in req_keys):                       
        return True                                                          
    raise CustomException("Not all keys present in dictionary")

我在pythonfiddle.com上添加了一个小提琴。

Answer 4

使用any功能：

if any(k not in temp_dict for k in ('key', 'key1', 'key2', 'key3')):
    raise CustomException("Some keys are missing from dict")

Answer 5

执行此操作的最Pythonic方法是使用循环：

>>> class CustomException(Exception):
...     pass
...
>>> keys = 'key0 key1 key2 key3'.split()
>>> my_dict = {k: v for k, v in zip(keys, xrange(4))}
>>>
>>> for k in keys:
...     if not k in my_dict:
...         raise CustomException('Key %s not in dictionary.' % k)
...
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
__main__.CustomException: Key key4 not in dictionary.
>>>

然而，更加Pythonic的方法是让你的函数在你使用函数时为函数中的每个必需键做一个try/except。例如：

>>> keys = 'key0 key1 key2 key3 key4'.split()
>>>
>>> def f(my_dict):
...     for key in keys:
...         try:
...             print k, my_dict[k]
...         except KeyError:
...             raise CustomException('Key %s not in dictionary.' % k)
...
>>> my_dict = {k: v for k, v in zip(keys[:-1], xrange(len(keys) - 1))}
>>> assert my_dict == {'key0': 0, 'key1': 1, 'key2': 2, 'key3': 3}  # Note no 'key4'
>>> f(my_dict)
key4
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in f
__main__.CustomException: Key key4 not in dictionary.
>>>

这被称为“比宽容更容易获得宽恕”（或“EAFP”）原则。继续你打算做什么，直到某些事情阻止你。

Python检查字典对象以获取正确的键抛出自定义异常

5 个答案: