How to create 10 random x, y coordinates in a grid using Python

I need to create a 8x8 grid and distribute 10 coins in random positions on the grid. The problem I am facing is that the randint function will sometimes generate the same random co-ordinates and therefore only 9 or 8 coins are generated and placed on the grid. How can I make sure this doesn't happen? Cheers :) This is my code so far:

from random import randint

grid = []
#Create a 8x8 grid
for row in range(8):
    grid.append([])
    for col in range(8):
        grid[row].append("0")

#create 10 random treasure chests
    #problem is that it might generate the same co-ordinates and therefore not enough coins
for coins in range(10):
    c_x = randint(0, len(grid)-1)
    c_y = randint(0, len(grid[0])-1)
    while c_x == 7 and c_y == 0:
           c_x = randint(0, len(grid)-1)
           c_y = randint(0, len(grid[0])-1)
    else:
        grid[c_x][c_y] = "C"

for row in grid:
print(" ".join(row))

I have included a while/else - as there must not be a coin in the bottom left corner of the grid