Problem:
Locator methods return the location where the event starts, not where it ends.
Locator line numbers start at 1, Locator column numbers can be 0.

Proposal:
Adapt documentation.

From the docs:
Instances of Locator provide these methods:

Locator.getColumnNumber() 
Return the column number where the current event ends.

Locator.getLineNumber() 
Return the line number where the current event ends

My Test:

import xml.sax

data = b"""<main>
    <sub
        attr="1"
        id="name"
        >
        <subsub />
    </sub>
</main>"""


class MyHandler(xml.sax.handler.ContentHandler):

    def startElement(self, name, attrs):
        if name == "sub":
            print("open", name, self._locator.getLineNumber(), self._locator.getColumnNumber())
            
    def endElement(self, name):
        if name == "sub":
            print("close", name, self._locator.getLineNumber(), self._locator.getColumnNumber())

xml.sax.parseString(data, MyHandler())

Output:

open sub 2 4
close sub 7 4

@patrick please accept our apologies for the delay in getting back to you.

The reported behavior has been verified -- the documented behavior is indeed incorrect for both Locator.getColumnNumber() and Locator.getLineNumber(). The beginning line and column numbers are returned, not the end.

This has been tested and verified for Python 2.7, Python 3.5.1 and a local build of the current default branch.

Thanks Emily.  For some reason the auto update of the tracker doesn't seem to have worked.  Maybe it is just delayed, but in case, the commit hashes are 2.7 97b76fe183f4, 3.5 9d6a9e2ae18b, and 3.6 cce04851d2e2.

New changeset 97b76fe183f4 by R David Murray in branch '2.7':
#13784: fix xml.sax.reader getColumn/LineNumber docs.
https://hg.python.org/cpython/rev/97b76fe183f4

New changeset 9d6a9e2ae18b by R David Murray in branch '3.5':
#13784: fix xml.sax.reader getColumn/LineNumber docs.
https://hg.python.org/cpython/rev/9d6a9e2ae18b

New changeset cce04851d2e2 by R David Murray in branch 'default':
Merge: #13784: fix xml.sax.reader getColumn/LineNumber docs.
https://hg.python.org/cpython/rev/cce04851d2e2