Crossword Genius

What constricts prey though often going empty (6)

Ross

I believe the answer is:

python

I'm a little stuck... Click here to teach me more about this clue!

'often going empty' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'what constricts prey though' is the wordplay.
I cannot really see how this works, but
'though' could be 'tho' (synonyms) and 'tho' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for python that I've seen before include "Heavy-bodied snake" , "Dragon killed by Apollo at Delphi" , "Constrictor snake" , "Large constricting snake" , "Large snake that kills prey by crushing" .)

I've seen this clue in The Times.
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