python: why does replace not work?

Question

I wrote a quick script to remove the 'http://' substring from a list of website addresses saved on an excel column. The function replace though, doesn't work and I don't understand why.

from openpyxl import load_workbook

def rem(string):
    print string.startswith("http://")    #it yields "True"
    string.replace("http://","")
    print string, type(string)    #checking if it works (it doesn't though, the output is the same as the input)

wb = load_workbook("prova.xlsx")
ws = wb["Sheet"]

for n in xrange(2,698):
    c = "B"+str(n)
    print ws[c].value, type(ws[c].value)   #just to check value and type (unicode)
    rem(str(ws[c].value))    #transformed to string in order to make replace() work

wb.save("prova.xlsx")    #nothing has changed

Answer 1

String.replace(substr)

does not happen in place, change it to:

string = string.replace("http://","")