# s1 == source string
# char == find this character
# repl == replace with this character
def findreplace(s1, char, repl):
s1 = s1.replace(char, repl)
return s1
# find each 'i' in the string and replace with a 'u'
print findreplace('it is icy', 'i', 'u')
# output
''' ut us ucy '''