[英]Python: How to access the dictionary that has specific key-values in a list
我有一個詞典列表:
[
{"START":"Denver", "END":"Chicago", "Num":0},
{"START":"Dallas", "END":"Houston", "Num":3},
{"START":"Virginia", "END":"Boston", "Num":1},
{"START":"Washington", "END":"Maine", "Num":7}
]
如何訪問此列表中具有"START":"Virginia", "END":"Boston"
的字典"START":"Virginia", "END":"Boston"
以大多數pythonic方式?
最恐怖的方式可能是列表理解:
[ d for d in dict_list if d["START"] == "Virginia" and d["END"] == "Boston" ]
作為mgilson指出,如果假設只有一個在與該對位置列表中的項目,您可以使用next
具有相同發電機表達,而不是括號。 這將返回匹配的dict,而不是包含它的單項列表:
trip = next( d for d in dict_list
if d["START"] == "Virginia" and d["END"] == "Boston" )
無論哪種方式,結果都引用與原始列表相同的dict對象,因此您可以進行更改:
trip["Num"] = trip["Num"] + 1
當通過原始列表訪問時,這些更改將在那里:
print(dict_list[2]["Num"]) # 2
正如Ashwini Chaudhary在他的回答中指出的那樣,你的搜索本身可能被指定為詞典。 在這種情況下,生成器表達式中的if
條件稍有不同,但邏輯在其他方面是相同的:
search = { "START": "Virginia", "END": "Boston" }
trip = next(d for d in dict_list if all(i in d.items() for i in search.items()))
在dict.items()
使用all()
dict.items()
:
In [66]: lis=[
....: {"START":"Denver", "END":"Chicago", "Num":0},
....: {"START":"Dallas", "END":"Houston", "Num":3},
....: {"START":"Virginia", "END":"Boston", "Num":1},
....: {"START":"Washington", "END":"Maine", "Num":7}
....: ]
In [67]: for x in lis:
....: if all(y in x.items() for y in search.items()):
....: x['Num']="foobar" #change Num here
....:
In [68]: lis
Out[68]:
[{'END': 'Chicago', 'Num': 0, 'START': 'Denver'},
{'END': 'Houston', 'Num': 3, 'START': 'Dallas'},
{'END': 'Boston', 'Num': 'foobar', 'START': 'Virginia'},
{'END': 'Maine', 'Num': 7, 'START': 'Washington'}]
使用list comprehension
:
In [58]: [x for x in lis if all(y in x.items() for y in search.items())]
Out[58]: [{'END': 'Boston', 'Num': 1, 'START': 'Virginia'}]
如果你要進行很多次搜索,並且你知道每對位置都有一個且只有一個dict,你可以從列表中創建一個dict,如下所示:
d = dict(((x['START'], x['END']), x) for x in list_of_dicts)
然后在新的字典中進行查找,如下所示:
found_dict = d[('Virginia', 'Chicago')]
您可以根據需要更改found_dict
。
如果每個項目都是唯一的,那么您可以這樣做:
def get_dict(items, start, end):
for dict in items:
if dict['START'] == start and dict['END'] == end:
return dict
接着:
>>> items = [
{"START":"Denver", "END":"Chicago", "Num":0},
{"START":"Dallas", "END":"Houston", "Num":3},
{"START":"Virginia", "END":"Boston", "Num":1},
{"START":"Washington", "END":"Maine", "Num":7}
]
>>> get_dict(items, 'Virginia', 'Boston')
{"START":"Virginia", "END":"Boston", "Num":1}
它相當簡單,但我認為我會為了完整性而發布它。
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