[Python-Dev] PySequence_Check but no len (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Fri Jun 22 20:08:24 EDT 2018

Ivan Pozdeev via Python-Dev wrote:

the documentation seems to use "sequence" in the sense "finite iterable". Functions that need to know the length of input in advance seem to be the minority.

The official classifications we have are:

Sequence: iter, getitem, len

Iterable: iter

There isn't any official term for a sequential thing that has iter and getitem but not len.

That's probably because the need for such a thing doesn't seem to come up very much. One usually processes a potentially infinite sequence by iterating over it, not picking things out at arbitrary positions. And usually its items are generated by an algorithm that works sequentially, so random access would be difficult to implement.

-- Greg

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