javascript在python中的_.where
javascript在python中的_.where
提问于 2015-11-17 02:10:49
在http://underscorejs.org/，有一家名为underscorejs的实用程序where，
_.where(listOfPlays, {author: "Shakespeare", year: 1611}它回来了，
[{title: "Cymbeline", author: "Shakespeare", year: 1611},
{title: "The Tempest", author: "Shakespeare", year: 1611}]如果不使用for in迭代，我如何在python中做到这一点？
回答 3
Stack Overflow用户
回答已采纳
发布于 2015-11-17 02:21:54
就我个人而言，我想使用清单理解。然而，它确实涉及到for和in
>>> listOfPlays = [{'title': x, 'author': x, 'year': 1611} for x in ('Shakespeare', 'someone')]
>>> listOfPlays
[{'author': 'Shakespeare', 'year': 1611, 'title': 'Shakespeare'}, {'author': 'someone', 'year': 1611, 'title': 'someone'}]
>>>
>>> [x for x in listOfPlays if x['author'] == 'Shakespeare' and x['year'] == 1611]
[{'author': 'Shakespeare', 'year': 1611, 'title': 'Shakespeare'}]或者，您可以使用filter
>>> filter(lambda x: x['author'] == 'Shakespeare' and x['year'] == 1611, listOfPlays)
[{'author': 'Shakespeare', 'year': 1611, 'title': 'Shakespeare'}]编辑：请注意，上面的示例是在Python2中计算的。在Python3中，内置函数filter返回一个可迭代函数，而不是一个列表。
Stack Overflow用户
发布于 2015-11-17 02:29:21
请注意，filter(function, iterable)等同于[item for item in iterable if function(item)]
def filter_by_dict(list_of_dicts, conditions):
def _check(item):
# returns True only if first is subset of second
# in python3 you should use items()
return conditions.viewitems() <= item.viewitems()
return filter(_check, list_of_dicts)
TEST = [
{"title": "Cymbeline", "author": "Shakespeare", "year": 1611},
{"title": "Otherr", "author": "Shakespeare", "year": 1612},
{"title": "The Tempest", "author": "Shakespeare", "year": 1611}
]
print(filter_by_dict(TEST, {"author": "Shakespeare", "year": 1611}))Stack Overflow用户
发布于 2015-11-17 03:48:45
作为列表理解，相当于_.where的代码可以在1行中用python编写，但它将使用for ... in语法：
def where(elems, **kwargs):
"""where(iterable, **filter_conditions) --> filtered iterable"""
return [el for el in elems if all(el.get(k) == v for k, v in kwargs.items())]或者，使用filter &map来避免使用for ... in
def where(elems, **kwargs):
"""where(iterable, **filter_conditions) --> filter object"""
def picker(elem):
return all(map(lambda x: elem.get(x[0]) == x[1], kwargs.items()))
return filter(picker, elems)在python 2中，两个版本的where函数都被调用为：
where(listOfPlays, author='Shakespeare', year=1611)在python 3上，后一个版本需要包装在一个列表中，因为filter返回一个过滤器对象，即
list(where(listOfPlays, author='Shakespeare', year=1611))页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/33747992
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