Differences creating tuples and collections.namedtuples

John Reid johnbaronreid at gmail.com
Mon Feb 18 12:47:35 CET 2013


Hi,

I was hoping namedtuples could be used as replacements for tuples in all instances. There seem to be some differences between how tuples and namedtuples are created. For example with a tuple I can do:

a=tuple([1,2,3])

with namedtuples I get a TypeError:

from collections import namedtuple
B=namedtuple('B', 'x y z')
b=B([1,2,3])

TypeError: __new__() takes exactly 4 arguments (2 given)
> <ipython-input-23-d1da2ef851fb>(3)<module>()
      1 from collections import namedtuple
      2 B=namedtuple('B', 'x y z')
----> 3 b=B([1,2,3])

I'm seeing this problem because of the following code in IPython:

def canSequence(obj):
    if isinstance(obj, (list, tuple)):
        t = type(obj)
        return t([can(i) for i in obj])
    else:
        return obj

where obj is a namedtuple and t([can(i) for i in obj]) fails with the TypeError. See http://article.gmane.org/gmane.comp.python.ipython.user/10270 for more info.

Is this a problem with namedtuples, ipython or just a feature?

Thanks,
John.




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