What the differences between these 3 for loops?

def generate_coor(dimension_x,dimension_y):
    x,y=int(dimension_x/2),int(dimension_y/2)
    for i in range(0, x + 1):
        print(x)
        x=x+1

generate_coor(100,27)

The above code does terminate.

def generate_coor(dimension_x,dimension_y):
    x,y=int(dimension_x/2),int(dimension_y/2)
    for i in range(0, x + 1):
        for j in range(0, y + 1):
            print(y)
            y=y+1

generate_coor(100,27)

The above code does not terminate

def generate_coor(dimension_x,dimension_y):
    x,y=int(dimension_x/2),int(dimension_y/2)
    for i in range(0, y):
        for j in range(0, y + 1):
            print(y)
            y=y+1

The above code does terminate

What the differences between these 3 examples? According to the code, each iteration for x or y should be increase by 1 hence the loop should not terminate but some terminate, some does not?

All loops will terminate, but the time to do so depends on the value you enter as parameter inputs.

What happens in your 2nd example :

def generate_coor(dimension_x,dimension_y):
    x,y=int(dimension_x/2),int(dimension_y/2)
    for i in range(0, x + 1):
        for j in range(0, y + 1):
            print(y)
            y=y+1

is that your nested loop for j in range(0, y + 1) is repeating itself for each iteration of the first loop for i in range(0, x + 1). This is particularly time consuming in your case with generate_coor(100,27) being given the CPU time required to execute the function will be exponential with respect to your two integer inputs.

If you take lower values, e.g. generate_coor(10,10), you'll see the function exiting.