def trim(s): i=0 n=1 while i<len(s): if s[:i]==" ": i=i+1 s=s[i:len(s)] else: break while n<len(s): if s[-n:]==" ": n=n+1 s=s[:-n] else: break return s

or


def trim(s):
while s[:1]==" ":
    s=s[1:]
while s[-1:]==" ":
    s=s[:-1]
return s