Program Arcade Games: Ch 16 Worksheet 2D-Array Algorithm
Welcome to Code Review, few suggestions:

Instead of calling .format() you can use f-Strings: print(f&quot;#{i} is the one.&quot;)
Is better to return the result, instead of printing in the method and break
You can use all() to test the celebrity and make the code more compact.

Applying the suggestions:
def check_celebrity(grid):
    for i in range(len(grid)):
        # Check if i is a candidate celebrity
        if grid[i][i] == 1 and grid[i].count(1) == 1:
            # Ensure that i is a celebrity
            if all(grid[j][i] == 1 for j in range(len(grid))):
                return i

Test:
grid = [ [1, 0, 0, 0],
         [1, 0, 0, 0],
         [1, 0, 1, 0],
         [1, 0, 1, 0] ]

print(f&quot;#{check_celebrity(grid)} is the one.&quot;)
# Outputs: #0 is a celebrity