✘namedtuples overly limited

Eric S. Raymond esr at thyrsus.com
Fri Sep 9 05:43:47 UTC 2016

Gary E. Miller <gem at rellim.com>:
> Yo All!
> 2nd Python undocumented limitation:
> https://docs.python.org/2.7/library/collections.html?highlight=namedtuples#collections.namedtuple
> namedtuples makes no mention of a limitation on the number of elements in
> a namedtuple.
> But:
> >>> a = collections.namedtuple('a', 'b', 'c', 'd', 'e')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: namedtuple() takes at most 4 arguments (5 given)

Your invocation syntax is wrong. You failed to notice that arg 2 is a list.
The correct way to do what you want is

a = collections.namedtuple("mytype", ['a', 'b', 'c', 'd', 'e'])

giving the tuple field names as a list of strings.  The value of a will be
the new lightweight class object with the name "mytype".

The argument prototype on that page was trying to clue you in.  Look
where it says:

collections.namedtuple(typename, field_names[, verbose=False][, rename=False])

Four formal args, two optional, and the second formal is a plural.

Good job spotting this feature, though.  I only learned of it last week.
It's a real aid to readability.
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
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