Countdown Clock: 01:05

Apart from formatting your time as minutes and seconds, you'll need to print a carriage return. Set end to \r:

import time

def countdown(t):
    while t:
        mins, secs = divmod(t, 60)
        timeformat = '{:02d}:{:02d}'.format(mins, secs)
        print(timeformat, end='\r')
        time.sleep(1)
        t -= 1
    print('Goodbye!\n\n\n\n\n')

This ensures that the next print overwrites the last line printed:

Here is the code which counts from 01:05 to 00:00 in MM:SS format.

Python 3 :

import time
def countdown(p,q):
    i=p
    j=q
    k=0
    while True:
        if(j==-1):
            j=59
            i -=1
        if(j > 9):  
            print(str(k)+str(i)+":"+str(j), end="\r")
        else:
            print(str(k)+str(i)+":"+str(k)+str(j), end="\r")
        time.sleep(1)
        j -= 1
        if(i==0 and j==-1):
            break
    if(i==0 and j==-1):
        print("Goodbye!", end="\r")
        time.sleep(1)
countdown(1,5) #countdown(min,sec)

Python 2 :

import time
def countdown(p,q):
    i=p
    j=q
    k=0
    while True:
        if(j==-1):
            j=59
            i -=1
        if(j > 9):  
            print "\r"+str(k)+str(i)+":"+str(j),
        else:
            print "\r"+str(k)+str(i)+":"+str(k)+str(j),
        time.sleep(1)
        j -= 1
        if(i==0 and j==-1):
            break
    if(i==0 and j==-1):
        print "\rGoodbye!"
        time.sleep(1)
countdown(1,5) #countdown(min,sec)