像字典一样搜索一个namedtuple

Question

为了节省内存并避免冗余数据库存储(可能是预优化),我使用的是namedtuple而不是字典.

但我需要搜索recs的集合,我的字典方法是:

import operator
def query(D,key,val, keynotfound=None):
    '''
    D:  a list of dictionaries  (but I want it to be namedtuples)
    key:  the key to query
    val:  the value to search for
    keynotfound:  value if key is not found

    Returns elements in D such that operator(D.get(key,None), val) is true
    '''
    op = operator.eq
    def try_op(f,x,y):
        try:
            return f(x,y)
        except Exception, exc:
            return False

    return (x for x in D if try_op(op, x.get(key,keynotfound),val))

没有在namedtuple上工作任何关于如何子类化namedtuple以使其像dict一样可搜索的技巧？并非每个实例都包含与查询键相同的键/字段,因此我需要跳过该行而不是抛出键/ attr错误.

Answer 1

我认为您可以使用getattr以查看该字段是否存在,如果不存在则引发异常或返回默认值.

例如,基于namedtuple文档:

from collections import namedtuple
Point = namedtuple('Point', ['x', 'y'])

# An instance of the namedtuple
p = Point(1, 2)

In [1]: getattr(p, "x")
Out[1]: 1

In [2]: getattr(p, "z")
...
AttributeError: 'Point' object has no attribute 'z'

In [3]: getattr(f, "z", None)
Out[3]: None