>>> from functools import reduce
>>> def xreplace(s, srch, rplc, count=-1):
... return reduce(lambda p, e: p.replace(e, rplc, count), srch, s)
>>> xreplace('are you mango', 'aeiou', '-', 1)
'-r- y-- mango'
>>> xreplace('are you mango', 'aeiou', '-')
'-r- y-- m-ng-'