Pygame: Weird sprite offset when flipped?

Question

I am working on a Mario based parkour/freerunning game. And the problem in question occurs when I am moving to the left, Mario's sprite is pushed back a few pixels when turned to the left. So relative to the sprite's rect, the image is a few pixels away from the wall it is colliding with.

I drew a red box around the rect to show what I mean:

I am not sure what is going on, I am using a sprite sheet for the animation, and when running to the left, it loads the appropriate frame image and then flips it.. so do I need to create a whole new sheet for running to the left or what? I am stumped.

Sorry if this question isn't descriptive enough, I am having trouble describing this..

Here is the code and a link to all the files:

import pygame
from pygame.locals import *
from collections import namedtuple

pygame.init()
screen=pygame.display.set_mode((640,480))
stand=pygame.image.load('images/stand.png').convert();stand.set_colorkey((255,255,255))
run_strip=pygame.image.load('images/run_strip.png').convert();run_strip.set_colorkey((255,255,255))
block1=pygame.image.load('images/block1.png')
p1=stand
clock=pygame.time.Clock()
px=0
py=30
f=8
direct=0
Move = namedtuple('Move', ['up', 'left', 'right'])
move = Move(0,0,0)
max_gravity = 100

def spr_fromsheet(spriteLocX, spriteLocY, spriteSizeX, spriteSizeY, sheetName):

    sheet = sheetName

    sprite = sheet.subsurface(pygame.Rect(spriteLocX, spriteLocY, spriteSizeX, spriteSizeY)) #grabs the sprite at this location

    return sprite
rectexample=pygame.image.load('images/mariomask.png')
class Player(object):
    sprite=rectexample
    def __init__(self, x, y):
        self.rect = self.sprite.get_rect(centery=y, centerx=x)
        # indicates that we are standing on the ground
        # and thus are "allowed" to jump
        self.on_ground = True
        self.xvel = 0
        self.yvel = 0
        self.jump_speed = 5
        self.move_speed = 2

    def update(self, move, blocks):
        # check if we can jump 
        if move.up and self.on_ground:
            self.yvel -= self.jump_speed

        # simple left/right movement
        if move.left:
                self.xvel = -self.move_speed
        if move.right:
                self.xvel = self.move_speed

        # if in the air, fall down
        if not self.on_ground:
            self.yvel += 0.3
            # but not too fast
            if self.yvel > max_gravity: self.yvel = max_gravity

        # if no left/right movement, x speed is 0, of course
        if not (move.left or move.right):
            self.xvel = 0

        # move horizontal, and check for horizontal collisions
        self.rect.left += self.xvel
        self.collide(self.xvel, 0, blocks)

        # move vertically, and check for vertical collisions
        self.rect.top += self.yvel
        self.on_ground = False;
        self.collide(0, self.yvel, blocks)

    def collide(self, xvel, yvel, blocks):
        # all blocks that we collide with
        for block in [blocks[i] for i in self.rect.collidelistall(blocks)]:

            # if xvel is > 0, we know our right side bumped 
            # into the left side of a block etc.
            if xvel > 0:
                    self.rect.right = block.rect.left
            if xvel < 0:
                    self.rect.left = block.rect.right

            # if yvel > 0, we are falling, so if a collision happpens 
            # we know we hit the ground (remember, we seperated checking for
            # horizontal and vertical collision, so if yvel != 0, xvel is 0)
            if yvel > 0:
                self.rect.bottom = block.rect.top
                self.on_ground = True
                self.yvel = 0
            # if yvel < 0 and a collision occurs, we bumped our head
            # on a block above us
            if yvel < 0: self.rect.top = block.rect.bottom

class Block(object):
    def __init__(self,x,y,sprite):
        self.x=x
        self.y=y
        self.sprite=sprite
        self.rect=self.sprite.get_rect(x=self.x,y=self.y)

blocks=[]
player=Player(40,40)
while True:
    screen.fill((15,20,150))
    key=pygame.key.get_pressed()
    move = Move(key[K_w], key[K_a], key[K_d])

    if key[K_d]:
        direct=0
        try:
            p1=spr_fromsheet(f,0,28,37,run_strip)
            f+=40
        except:
            f=8
    elif key[K_a]:
        direct=1
        try:
            p1=spr_fromsheet(f,0,28,37,run_strip)
            p1=pygame.transform.flip(p1,1,0)
            f+=40
        except:
            f=8
    else:
        if direct==0:
            p1=stand
        else:
            p1=pygame.transform.flip(stand,1,0)

    for e in pygame.event.get():
        if e.type==QUIT:
            exit()
        if e.type==MOUSEBUTTONUP:
            if e.button==1:
                blocks.append(Block((pygame.mouse.get_pos()[0]/16)*16,(pygame.mouse.get_pos()[1]/16)*16,block1))
            if e.button==3:
                player=Player((pygame.mouse.get_pos()[0]/16)*16,(pygame.mouse.get_pos()[1]/16)*16)

    for b in blocks:
        screen.blit(b.sprite,b.rect)
    player.update(move,blocks)
    screen.blit(p1,player.rect)
    clock.tick(60)
    pygame.draw.rect(screen, (255,0,0), player.rect, 1)
    pygame.display.update()

Files: http://host-a.net/u/PlanetForgeGame/game.zip

Answer 1

I didn't look too far into your code, but I think your problem has something to do with the images not ending where the last "significant pixel" is, if you know what I mean. For example, if X's are colored pixels and O's are white, you have

OOOXXXXX
OOOXXXXX
OOOXXXXX

instead of

XXXXXX
XXXXXX
XXXXXX

I hope this makes sense.