Implement python replace() function without using regexp

I'm trying to rewrite the equivalent of the python replace() function without using regexp. Using this code, i've managed to get it to work with single chars, but not with more than one character:

def Replacer(self, find_char, replace_char):
    s = []
    for char in self.base_string:
        if char == find_char:
            char = replace_char
        #print char
        s.append(char)
    s = ''.join(s)

my_string.Replacer('a','E')

Anybody have any pointers how to make this work with more than one character? example:

my_string.Replacer('kl', 'lll') 

How clever are you trying to be?

def Replacer(self, find, replace):
    return(replace.join(self.split(find)))

>>> Replacer('adding to dingoes gives diamonds','di','omg')
'adomgng to omgngoes gives omgamonds'

Here is a method that should be pretty efficient:

def replacer(self, old, new):
    return ''.join(self._replacer(old, new))

def _replacer(self, old, new):
    oldlen = len(old)
    i = 0
    idx = self.base_string.find(old)
    while idx != -1:
        yield self.base_string[i:idx]
        yield new
        i = idx + oldlen
        idx = self.base_string.find(old, i)
    yield self.base_string[i:]