Can somebody explain this behavior in pygame?

Question

I have an image that I'm rotating and moving

And when the rotation angle is negative the image moves as expected.

But when the angle is positive it moves it's origing point to the left

Can anybody explain this behavior, and how to solve it?

Here is the code

import pygame, sys
import math

screen = pygame.display.set_mode((700, 400))
wrench = pygame.image.load('prueba.bmp')
white = (255,255,255)


ox = 20
oy = 32
running = True
posX = 100 - ox
posY = 100 - oy


pygame.init()
while running:
    event = pygame.event.poll()
    if event.type == pygame.QUIT:
        running=0
        screen.blit(wrench, (posX, posY))
    if(pygame.time.get_ticks() <= 20000):
        screen.fill(white)
        t = pygame.time.get_ticks() / 1000
        ang = math.degrees(math.pi / 2 * math.cos(math.pi * t))
        #ang = math.pi / 2 * math.cos(math.pi * t)
        print(ang)
        posX = 100 + (50 * math.cos(math.pi * t)) - ox 
        posY = 100 + (20 * math.sin(math.pi * t)) - oy
        rotated_wrench = pygame.transform.rotate(wrench, ang)
        screen.blit(rotated_wrench, (posX, posY))
    pygame.display.flip()

Answer 1

This line is setting the X coordinate of the bliting:

posX = 100 + (50 * math.cos(math.pi * t)) - ox

The cosine is positive from 0 to 90 degrees and 270 to 0, which is the right side of a circle; and negative otherwise.

This is making the value to oscillate between 100 + 50 - ox and 100 - 50 - ox

If you want to keep the horizontal position to not oscillate in both directions, you should use the absolute value:

posX = 100 + (50 * math.fabs(math.cos(math.pi * t))) - ox