Getting exactly one element or raising exception with lxml xpath

Question

The xpath() function in lxml normally returns a list of elements.

If I have an XPath which I expect to return exactly one element, what's the nicest way to:

Check that one element is returned or else raise an exception, and:
Get that element (as opposed to a one-element list)?

I'm really looking for the analogue of SQLAlchemy's one() function.

score 19 · Accepted Answer · answered Sep 27 '12 at 06:37

19

try:
    (element,) = tree.xpath('//xpath/selector')
except ValueError:
    raise InvalidSelector()
    # happened because the list was either empty or contained multiple elements

answered Sep 27 '12 at 06:37

andrean

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Nice! I didn't know you could unpack a list against a tuple. – mskel Sep 27 '12 at 07:27
really nice and simple solution – pictuga Oct 19 '13 at 22:52

Getting exactly one element or raising exception with lxml xpath

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