Python 地图有链吗？

发布于 2024-11-01 13:18:34 字数 377 浏览 2 评论 0原文

在Python中，可以使用itertools.chain以惰性方式扩展列表：

L = itertools.chain(L1, L2)

是否有惰性映射“粘合”运算符？即，

M = glue(M1, M2)

其中

M['blah']

M1['blah'] if 'blah' in M1 else M2['blah']

and，M 具有适当的 keys() 和 values() 生成器。

原文

In Python, it's possible to extend a list in a lazy way by using itertools.chain:

L = itertools.chain(L1, L2)

Is there a lazy map "gluing" operator? I.e.,

M = glue(M1, M2)

where

M['blah']

returns

M1['blah'] if 'blah' in M1 else M2['blah']

and, M has appropriate generators for keys() and values().

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枕头说它不想醒 2024-11-08 13:18:34

Python 3.3 添加了 collections.ChainMap 来实现这一点。

回复收藏 0 原文

音盲 2024-11-08 13:18:34

构建一个类来表示针对映射列表的惰性求值，并根据您的应用程序定制行为是很简单的。例如：

from UserDict import DictMixin

class Map(object, DictMixin):
    def __init__(self, *maps):
        self.maps = maps
    def __getitem__(self, key):
        for m in self.maps:
            if key in m:
                return m[key]
    def keys(self):
        return list(self.iterkeys())
    def iterkeys(self):
        return (k for m in self.maps for k in m.iterkeys())
    def values(self):
        return list(self.itervalues())
    def itervalues(self):
        return (v for m in self.maps for v in m.itervalues())

def glue(*maps):
    return Map(*maps)

M1 = {'blah': 1}
M2 = {'duh': 2}

M = glue(M1, M2)
print M['blah']
print M['duh']
print list(M.keys())
print list(M.values())

输出：

1
2
['blah', 'duh']
[1, 2]

It's straightforward to build a class to represent lazy evaluations against a list of maps, and tailor the behavior to your application. For example:

from UserDict import DictMixin

class Map(object, DictMixin):
    def __init__(self, *maps):
        self.maps = maps
    def __getitem__(self, key):
        for m in self.maps:
            if key in m:
                return m[key]
    def keys(self):
        return list(self.iterkeys())
    def iterkeys(self):
        return (k for m in self.maps for k in m.iterkeys())
    def values(self):
        return list(self.itervalues())
    def itervalues(self):
        return (v for m in self.maps for v in m.itervalues())

def glue(*maps):
    return Map(*maps)

M1 = {'blah': 1}
M2 = {'duh': 2}

M = glue(M1, M2)
print M['blah']
print M['duh']
print list(M.keys())
print list(M.values())

Output: