192.168.0.1:8000 = 2
192.168.0.10:80 = 1
192.168.0.100:3128 = 2
192.168.0.4:8080
192.168.0.5:7822 = 2
192.168.0.6:8005

searchValue = "192.168.0.10:80"
newNumber = 2

f = open("datafile.txt", "r+b")

for line in file:
    if line.split()[0] == searchValue:
        position = f.tell() - len(line) #the tell() method gives the current position in the file
        f.seek(position)
        f.write("%s = %d" % (searchValue, newNumber))
        break

f.close()