pac-man pygame issue random shifting of ghost

[gabi404]

Hello, first I'm French so if my english is bad it's normal.. For 2 years I learn Python at the school. And now I want make a pac-man with pygame. I started but for the random shifting of ghost I have an issue. When there is a collision with a ghost and a wall the ghost stops and don't change direction.

ps: if you find other errors in my code It's normal so tell me please. fonction_ghost.txt