Type code for ellipsis token doesn't match with the constant token.ELLIPSIS:
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import io
import token
import tokenize

source = "..."

tokens = list(tokenize.tokenize(io.BytesIO(source.encode('utf-8')).readline))
ellipsis = tokens[1]

print(ellipsis)
print(token.ELLIPSIS) 
-----------------------------------------

This code outputs following in Python 3.5 and 3.6:

> TokenInfo(type=53 (OP), string='...', start=(1, 0), end=(1, 3), line='...')
> 52

and following in Python 3.4

> TokenInfo(type=52 (OP), string='...', start=(1, 0), end=(1, 3), line='...')
> 51

Thank you for the report, but this behavior is already documented at https://docs.python.org/3/library/tokenize.html

    To simplify token stream handling, all Operators and Delimiters
    tokens are returned using the generic token.OP token type. The
    exact type can be determined by checking the exact_type property
    on the named tuple returned from tokenize.tokenize().

If you replace the following line

    print(ellipsis)

with

    print(ellipsis.exact_type)

you will see that it prints '52'.

But it looks like Ellipsis is neither operator nor delimiter: https://docs.python.org/3/reference/lexical_analysis.html#operators

If you look at https://docs.python.org/3/reference/lexical_analysis.html#delimiters '.' (period) is listed as delimiter and there is the following sentence to answer your question:

    A sequence of three periods has a special meaning as an ellipsis literal.

But ellipsis is a distinct token, not a sequence of three period tokens.

Also, I can't see how we could conceptually treat ellipsis as a delimiter or operator -- it's a literal.

I still think either documentation or implementation needs to be fixed here.

Please don't reopen an issue if it was closed by a core developer.

It's not clear to me what exactly do you want to change in the implementation or documentation.

     A sequence of three periods has a special meaning as an ellipsis literal.

is literally describes how the ELLIPSIS token is identified in Parser/tokenizer.c (see PyToken_ThreeChars in that file) So a sequence of three periods is identified as an ellipsis literal which is an expression in Python.

Do you want to change tokenize.tokenize() (it's in Lib/tokenize.py) so it will return

    TokenInfo(type=52 (ELLIPSIS), ...)

instead of

    TokenInfo(type=53 (OP), ...)

? Note that ELLIPSIS has been added to tokenize.EXACT_TOKEN_TYPES in issue 24622. To me, since it has been added to tokenize.EXACT_TOKEN_TYPES there is no need to special case ELLIPSIS in Lib/tokenize.py.

Or do you want to clarify

    To simplify token stream handling, all Operators and Delimiters tokens are returned using the generic token.OP token type.

at https://docs.python.org/3/library/tokenize.html?

(Sorry, I didn't mean to challenge the authority of a core developer. I simply didn't notice that adding a comment reopens the issue. I hope this time I selected correct parameters and this doesn't happen again)

I'm trying to rephrase my concern. 

Initially I thought there was a mistake in the tokenizer or in the token module.

After you pointed out the documentation about token.OP and exact_type, I'm worried about a smaller detail. The documentation only talks about *operators* and *delimiters* having type attribute set to token.OP. According to my understanding (and also the listings at https://docs.python.org/3/reference/lexical_analysis.html#operators), ellipsis is neither operator nor delimiter. 

Am I right about this? 

(I understand that the source representation of both ELLIPSIS and DOT tokens contains period *character(s)*, but I don't see why is this relevant when we discuss the properties of *tokens*)

Anyway, if ellipsis is neither operator nor delimiter, (and if there is a reason why it is treated similarly with operators and delimiters) then I recommend to update the documentation by replacing 

> all Operators and Delimiters tokens 
> are returned using the generic token.OP token type

with 

> all Operators, Delimiters and Ellipsis tokens
> are returned using the generic token.OP token type


(I understand, that this is not a serious issue. If you prefer not to discuss it further then I'm happy to leave it as it is.)

I think we should add 'and Ellipsis' in the tokenize doc to get
'all Operators and Delimiters tokens and Ellipsis are returned ...'.  I would actually prefer 'Operator and Delimiter tokens' but I don't know if the 's' is needed to trigger the current linkage.

Thank you for your detailed response, Aivar. I agree that adding 'and Ellipsis' would make the tokenize documentation clearer. Would you like to send a pull request?

Here is the PR: https://github.com/python/cpython/pull/3469

(It's my first, so I don't know if I should to also update NEWS file or add "skip news" label. I signed the CLA, so I hope this warning goes away.)

Once the CLA * shows up after your name, one of us should remove CLA needed tag and bot will verify.  I believe tagging as trivial would also work.

New changeset 5f8fbf917ebf2398aa75a1f271617e2e50ab7c88 by Mariatta (Aivar Annamaa) in branch 'master':
bpo-31394: Clarify documentation about token type attribute (GH-3469)
https://github.com/python/cpython/commit/5f8fbf917ebf2398aa75a1f271617e2e50ab7c88

New changeset 5513e888e9a742156c35ce7ab628407d8cf9e1f0 by Mariatta in branch '3.6':
[3.6] bpo-31394: Clarify documentation about token type attribute (GH-3469) (GH-3525)
https://github.com/python/cpython/commit/5513e888e9a742156c35ce7ab628407d8cf9e1f0

New changeset ea0f7c26cef4550bf4db1a9bae17d41b79ab7c0d by Mariatta in branch 'master':
bpo-31394: Make tokenize.rst PEP 8-compliant (GH-3526)
https://github.com/python/cpython/commit/ea0f7c26cef4550bf4db1a9bae17d41b79ab7c0d