adurdin at gmail.com
Sat Sep 4 13:27:04 CEST 2004
On Sat, 4 Sep 2004 11:00:30 +0200, Alex Martelli <aleaxit at yahoo.com> wrote:
> Pseudotuples with NAMED (as well as indexed) arguments, as modules stat
> and time now return, may be a different issue. Not sure why we never
> made declaring such pseudotuples as usertypes as easy as it should be, a
> custom metaclass in some stdlib module shd be enough. But tuples whose
> items can't be named, just indexed or sliced, just are not a good fit
> for the kind of use case you and Guido use to justify tuple's lack of
> methods, IMHO.
Such "pseudotuples" are easy enough to implement. Since I'm not all
that crash hot with metaclasses, I just made a tuple subclass (see
below). Would a metaclass implementation offer any significant
benefits over a subclass?
"""Builds a tuple with elements named and indexed.
A NamedTuple is constructed with a sequence of (name, value) pairs;
the values can then be obtained by looking up the name or the value.
def __new__(cls, seq):
return tuple.__new__(cls, [val for name,val in seq])
def __init__(self, seq):
tuple.__setattr__(self, "_names", dict(zip([name for name,val
in seq], range(len(seq)))))
def __getattr__(self, name):
return tuple.__getitem__(self, self.__dict__["_names"][name])
raise AttributeError, "object has no attribute named '%s'" % name
def __setattr__(self, name, value):
raise TypeError, "object doesn't support item assignment"
tuple.__setattr__(self, name, value)
if __name__ == "__main__":
names = ("name", "age", "height")
person1 = NamedTuple(zip(names, ["James", "26", "185"]))
person2 = NamedTuple(zip(names, ["Sarah", "24", "170"]))
for i,name in enumerate(names):
print name, ":", person2[i]
(Submitted to the Cookbook: recipe #303439)
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