Python / print and assign random number every time

I'm trying to generate a random integral and assign it to the variable.

import random
import time

Op = lambda: random.randint(1300, 19000)
op = "http://ift.tt/2m84JPr"

variable = int(Op())

grow = 0
while x < 3:
    print(Op())
    grow = grow + 1
    time.sleep(1)

In here everything works fine, function "print" prints different result every time with 3 attempts. However when I want to format this code like this:

Op = lambda: random.randint(1300, 19000)
op = "http://ift.tt/2m84JPr"

Op1 = int(Op())
pop = str("{}{}").format(op, Op1)


grow = 0
while grow < 3:
    print(pop)
    grow = grow + 1
    time.sleep(1)

Then the function print gives me the same number three times.

For example:

>>>http://ift.tt/2mPBYLI
>>>http://ift.tt/2mPBYLI
>>>http://ift.tt/2mPBYLI

And I would like to get three random numbers. For example:

    >>>http://ift.tt/2m80pzE
    >>>http://ift.tt/2mPI1Qf
    >>>http://ift.tt/2m7TkPt

I was trying to use %s - %d formatting but the result is the same.