[Python-Dev] More imformative iterator representations (original) (raw)

Robert Brewer fumanchu at amor.org
Tue Apr 6 22:00:31 EDT 2004

Raymond Hettinger wrote:

Armin's note reminded me that the only thing I do not like about using iterators is not being able to see their contents at the interactive prompt. So, I posted an idea about changing the print part of the read-eval-print loop to display more information:

>>> enumerate('abcdefgh') <enumerate object at 0x401a102c: (0, 'a') (1, 'b') (2, 'c') ...> There a couple of problems with the approach. One is how to identify an iterator object -- the presence of iter() and next() is a good but not perfect indicator.

Oh, I don't know. The Library Ref makes it pretty clear:

"The iterator objects themselves are required to support the following two methods, which together form the iterator protocol: iter() ... next() "

If not perfect, it's still a reasonable assumption. Since there's no Iterator superclass from which to inherit, you're going to have to rewrite each repr by hand anyway, and therefore can decide each one independently. Are there reasonable iterator objects which don't follow the "iterator protocol"?

An alternative to the read-eval-print approach is providing a custom repr() method for the builtin iterators.

+1.

Q: Are there any other candidate output formats? A: Yes, we could add length information for a more mathematical style output:

reversed(['h', 'g', 'f', ... to 8 objects])

The very presence of len might be a strong argument for providing the new repr, and its absence an indicator to avoid such.

Robert Brewer MIS Amor Ministries fumanchu at amor.org

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