Backstreet in Paris? Within it, the French and Swiss whizz (5)
I believe the answer is:
euler
'backstreet in paris?' is the definition.
The definition suggests a singular noun which matches the answer.
'within it the french and swiss whizz' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found in the answer.
'the french' could be 'le' ('the' in French) and 'le' is found within the answer.
The remaining letters 'ur' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for euler that I've seen before include "Swiss mathematician; sounds like lubricator" , "Swiss scientist" , "Leonhard -, Eighteenth century Swiss mathematician" , "Leonhard -, C-eighteen Swiss mathematician" , "18th-century Swiss mathematician and physicist" .)