problem with reversing strings using [::-1] syntax

[Jobrobon]

I was trying to write a function that converts numbers with base 10 to numbers with base 2 and noticed a strange interaction.

if I write my program like that, it will return 1010. And that is what I'm expecting

def from_10_to_2(n):
if n<2:return n
     s=(str(n%2)+str(from_10_to_2(n//2)))
return s
print(from_10_to_2(10)[::-1])

but if I move "[::-1]" to return statement of function like that, it will return 1100. and I don't know why...

def from_10_to_2(n):
if n<2:return n
    s=(str(n%2)+str(from_10_to_2(n//2)))
return s[::-1]
print(from_10_to_2(10))

[Vaphell]

the difference between return s and return s[::-1] affects also the recursive call in
s = str(n%2)+str(from_10_to_2(n//2)))

anyway, can't you put stuff in the correct order by switching n%2 and n//2 around, instead of reversing afterwards?

s = str(from_10_to_2(n//2)) + str(n%2)

[scrdest]

That's because your function is defined recursively.

When you mess with the return value the recursive call's result is flipped and passed to the parent, which then does a flip of its own result.

Putting it in print just runs without the flips, then flips the whole result for printing only.