class Pile:
    def __init__(self):
        self.objets = []
        
    def est_vide(self):
        return len(self.objets) == 0
    
    def empiler(self, objet):
        self.objets.append(objet)
        
    def depiler(self):
        if self.est_vide():
            print("La pile est vide")
            return None
        else:
            element = self.objets.pop()
            return element
    
    def trouver_sommet(self):
        if self.est_vide():
            print("La pile est vide")
            return None
        else:
            self.objets[-1]
            
    def taille_pile(self):
        return len(self.objets)
    
    def __str__(self):
        for i in range(len(self.objets)-1,-1,-1):
            print(self.objets[i])
        return ""
    
p = Pile()
p.empiler(13)
p.empiler(25)

print(p)

def bon_parenthesage(str):
    #à compléter
    pass
    
#assert bon_parenthesage("((()())(()))") == True
#assert bon_parenthesage("())(()") == False
#assert bon_parenthesage("(())(()") == False

def renverse(pile):
    #à compléter
    pass

def positifs(pile):
    #à compléter
    pass

#assert renverse([1, 2, 3, 4, 5]) == [5, 4, 3, 2, 1]
#assert positifs([-1, 0, 5, -3, 4, -6, 10, 9, -8]) == [0, 5, 4, 10, 9]
#assert positifs([-2]) == []