Strange output in recurtion.

Question

Why does it print "None" instead of 6?

https://code.sololearn.com/cUUHbt9FIES1/?ref=app

Answer 1

because you print a print statement

Your last line calls to print, but so does inside the function you call

Answer 2

at the end of function you return nothing
return digital_root(sum([int(i) for i in str(n)]))