我有一本嵌套的字典。是否只有一种方法可以安全地传递价值观?
try:
example_dict['key1']['key2']
except KeyError:
pass
或者python有一个类似get()的方法用于嵌套字典?
当前回答
一个简单的类，可以包装字典，并根据键进行检索:
class FindKey(dict):
def get(self, path, default=None):
keys = path.split(".")
val = None
for key in keys:
if val:
if isinstance(val, list):
val = [v.get(key, default) if v else None for v in val]
else:
val = val.get(key, default)
else:
val = dict.get(self, key, default)
if not val:
break
return val
例如:
person = {'person':{'name':{'first':'John'}}}
FindDict(person).get('person.name.first') # == 'John'
如果该键不存在，则默认返回None。你可以在FindDict包装器中使用default=键覆盖它，例如':
FindDict(person, default='').get('person.name.last') # == doesn't exist, so ''
其他回答
下面是一个基于unutbu函数答案的解决方案:
Python命名指南 默认值作为参数 不用try，只是检查key是否在object上
def safe_get(dictionary, *keys, default=None):
for key in keys:
if key not in dictionary:
return default
dictionary = dictionary[key]
return dictionary
递归法(мб п п и и одитс)
示例dict类型:
foo = [{'feature_name': 'Sample Creator > Contract Details > Elements of the page',
'scenarios': [{'scenario_name': 'SC, CD, Elements of the page',
'scenario_status': 'failed',
'scenario_tags': None,
'steps': [{'duration': 0,
'name': 'I open application Stage and login by '
'SPT_LOGIN and password SPT_PWD',
'status': 'untested'},
{'duration': 0,
'name': 'I open Sample Creator query page',
'status': 'untested'},
{'duration': 7.78166389465332,
'name': 'I open application Stage and login by '
'SPT_LOGIN and password SPT_PWD',
'status': 'passed'},
{'duration': 3.985326051712036,
'name': 'I open Sample Creator query page',
'status': 'passed'},
{'duration': 2.9063704013824463,
'name': 'Enter value: '
'X-2008-CON-007,X-2011-CON-016 in '
'textarea: project_text_area sleep: 1',
'status': 'passed'},
{'duration': 4.4447715282440186,
'name': 'I press on GET DATA',
'status': 'passed'},
{'duration': 1.1209557056427002,
'name': 'Verify the top table on Contract Details',
'status': 'passed'},
{'duration': 3.8173601627349854,
'name': 'I export contract_details table by offset '
'x:100, y:150',
'status': 'passed'},
{'duration': 1.032956600189209,
'name': 'Check data of '
'sc__cd_elements_of_the_page_1 and skip '
'cols None',
'status': 'passed'},
{'duration': 0.04593634605407715,
'name': "Verify 'Number of Substances' column "
'values',
'status': 'passed'},
{'duration': 0.10199904441833496,
'name': 'Substance Sample Details bottom table '
'columns',
'status': 'passed'},
{'duration': 0.0009999275207519531,
'name': 'Verify the Substance Sample Details '
'bottom table',
'status': 'passed'},
{'duration': 3.8558616638183594,
'name': 'I export substance_sample_details table '
'by offset x:100, y:150',
'status': 'passed'},
{'duration': 1.0329277515411377,
'name': 'Check data of '
'sc__cd_elements_of_the_page_2 and skip '
'cols None',
'status': 'passed'},
{'duration': 0.2879970073699951,
'name': 'Click on AG-13369',
'status': 'passed'},
{'duration': 3.800830364227295,
'name': 'I export substance_sample_details table '
'by offset x:100, y:150',
'status': 'passed'},
{'duration': 1.0169551372528076,
'name': 'Check data of '
'sc__cd_elements_of_the_page_3 and skip '
'cols None',
'status': 'passed'},
{'duration': 1.7484464645385742,
'name': 'Select all cells, table: 2',
'status': 'passed'},
{'duration': 3.812828779220581,
'name': 'I export substance_sample_details table '
'by offset x:100, y:150',
'status': 'passed'},
{'duration': 1.0029594898223877,
'name': 'Check data of '
'sc__cd_elements_of_the_page_2 and skip '
'cols None',
'status': 'passed'},
{'duration': 1.6729373931884766,
'name': 'Set window size x:800, y:600',
'status': 'passed'},
{'duration': 30.145705699920654,
'name': 'All scrollers are placed on top 6 and far '
'left 8',
'status': 'failed'}]}]},
{'feature_name': 'Sample Creator > Substance Sample History > Elements of the '
'page',
'scenarios': [{'scenario_name': 'SC, SSH, Elements of the page',
'scenario_status': 'passed',
'scenario_tags': None,
'steps': [{'duration': 0,
'name': 'I open application Stage and login by '
'SPT_LOGIN and password SPT_PWD',
'status': 'untested'},
{'duration': 0,
'name': 'I open Sample Creator query page',
'status': 'untested'},
{'duration': 7.305850505828857,
'name': 'I open application Stage and login by '
'SPT_LOGIN and password SPT_PWD',
'status': 'passed'},
{'duration': 3.500955104827881,
'name': 'I open Sample Creator query page',
'status': 'passed'},
{'duration': 3.0419492721557617,
'name': 'Enter value: NOA401800 SYN-NOA '
'A,S4A482070C SYN-ISN-OLD '
'O,S04A482167T,S04A482190Y,CSAA796564,CSCD106701 '
'in textarea: id_text_area sleep: 1',
'status': 'passed'},
{'duration': 49.567158460617065,
'name': 'I press on GET DATA',
'status': 'passed'},
{'duration': 0.13904356956481934,
'name': 'Open substance_sample_history',
'status': 'passed'},
{'duration': 1.1039845943450928,
'name': 'Columns displayed',
'status': 'passed'},
{'duration': 3.881945848464966,
'name': 'I export export_parent_table table by '
'offset x:100, y:150',
'status': 'passed'},
{'duration': 1.0334820747375488,
'name': 'Check data of '
'sc__ssh_elements_of_the_page_1 and skip '
'cols None',
'status': 'passed'},
{'duration': 0.0319981575012207,
'name': "Title is 'Additional Details for Marked "
"Rows'",
'status': 'passed'},
{'duration': 0.08897256851196289,
'name': 'Columns displayed (the same as in top '
'table)',
'status': 'passed'},
{'duration': 25.192569971084595,
'name': 'Verify the content of the bottom table',
'status': 'passed'},
{'duration': 4.308935880661011,
'name': 'I export '
'additional_details_for_marked_rows table '
'by offset x:100, y:150',
'status': 'passed'},
{'duration': 1.0089836120605469,
'name': 'Check data of '
'sc__ssh_elements_of_the_page_1 and skip '
'cols None',
'status': 'passed'}]}]}]
代码:
def get_keys(_dict: dict, prefix: list):
prefix += list(_dict.keys())
return prefix
def _loop_elements(elems:list, prefix=None, limit=None):
prefix = prefix or []
limit = limit or 9
try:
if len(elems) != 0 and isinstance(elems, list):
for _ in elems:
if isinstance(_, dict):
get_keys(_, prefix)
for item in _.values():
_loop_elements(item, prefix, limit)
return prefix[:limit]
except TypeError:
return
>>>goo = _loop_elements(foo,limit=9)
>>>goo
['feature_name', 'scenarios', 'scenario_name', 'scenario_status', 'scenario_tags', 'steps', 'duration', 'name', 'status']
已经有很多很好的答案，但我已经提出了一个类似于JavaScript领域的lodash get的函数，它也支持通过索引进入列表:
def get(value, keys, default_value = None):
'''
Useful for reaching into nested JSON like data
Inspired by JavaScript lodash get and Clojure get-in etc.
'''
if value is None or keys is None:
return None
path = keys.split('.') if isinstance(keys, str) else keys
result = value
def valid_index(key):
return re.match('^([1-9][0-9]*|[0-9])$', key) and int(key) >= 0
def is_dict_like(v):
return hasattr(v, '__getitem__') and hasattr(v, '__contains__')
for key in path:
if isinstance(result, list) and valid_index(key) and int(key) < len(result):
result = result[int(key)] if int(key) < len(result) else None
elif is_dict_like(result) and key in result:
result = result[key]
else:
result = default_value
break
return result
def test_get():
assert get(None, ['foo']) == None
assert get({'foo': 1}, None) == None
assert get(None, None) == None
assert get({'foo': 1}, []) == {'foo': 1}
assert get({'foo': 1}, ['foo']) == 1
assert get({'foo': 1}, ['bar']) == None
assert get({'foo': 1}, ['bar'], 'the default') == 'the default'
assert get({'foo': {'bar': 'hello'}}, ['foo', 'bar']) == 'hello'
assert get({'foo': {'bar': 'hello'}}, 'foo.bar') == 'hello'
assert get({'foo': [{'bar': 'hello'}]}, 'foo.0.bar') == 'hello'
assert get({'foo': [{'bar': 'hello'}]}, 'foo.1') == None
assert get({'foo': [{'bar': 'hello'}]}, 'foo.1.bar') == None
assert get(['foo', 'bar'], '1') == 'bar'
assert get(['foo', 'bar'], '2') == None
减少方法的改进很少，使其与列表一起工作。也使用数据路径作为字符串除以点，而不是数组。
def deep_get(dictionary, path):
keys = path.split('.')
return reduce(lambda d, key: d[int(key)] if isinstance(d, list) else d.get(key) if d else None, keys, dictionary)
虽然reduce方法简洁而简短，但我认为简单的循环更容易理解。我还包含了一个默认参数。
def deep_get(_dict, keys, default=None):
for key in keys:
if isinstance(_dict, dict):
_dict = _dict.get(key, default)
else:
return default
return _dict
作为理解reduce一行程序如何工作的练习，我执行了以下操作。但最终循环方法对我来说似乎更直观。
def deep_get(_dict, keys, default=None):
def _reducer(d, key):
if isinstance(d, dict):
return d.get(key, default)
return default
return reduce(_reducer, keys, _dict)
使用
nested = {'a': {'b': {'c': 42}}}
print deep_get(nested, ['a', 'b'])
print deep_get(nested, ['a', 'b', 'z', 'z'], default='missing')
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