Buggy python submission (verdict: Runtime Error):
import sys
class Tree():
    def __init__(self):
        self.root = None
    def insert(self, key):
        z = Node(key)
        y = None
        x = self.root
        while x:
            y = x
            if z.key < x.key:
                x = x.left
            else:
                x = x.right
        z.parent = y
        if y == None:
            self.root = z
        elif z.key < y.key:
            y.left = z
        else:
            y.right = z
    def find(self, key):
        x = self.root
        while x and x.key != key:
            if x.key < key:
                x = x.right
            else:
                x = x.left
        return x
    def delete(self, key):
        z = self.find(key)
        y = successor(z) if z.left and z.right else z
        x = y.left if y.left else y.right

        if x:
            x.parent = y.parent
        if y.parent == None:
            self.root = x 
        elif y == y.parent.left:
            y.parent.left = x
        else:
            y.parent.right = x
        if y != z:
            z.key = y.key
    def successor(x):
        if x.right:
            return minimum(x.right)
        y = x.parent
        while y and x == y.right:
            x = y
            y = y.parent
        return y

    def minimum(x):
        while x.left:
            x = x.left
        return x
    
    def print(self):
        print('',' '.join(map(str, self.root.inwalk())))
        print('',' '.join(map(str, self.root.prewalk())))
    
class Node():
    def __init__(self, key):
        self.key = key
        self.parent = self.left = self.right = None
    def prewalk(self):
        ret = [self.key]
        if self.left:
            ret += self.left.prewalk()
        if self.right:
            ret += self.right.prewalk()
        return ret
    def inwalk(self):
        ret = []
        if self.left:
            ret += self.left.inwalk()
        ret += [self.key]
        if self.right:
            ret += self.right.inwalk()
        return ret
tree = Tree()
n = sys.stdin.readline()
for line in sys.stdin:
    if line[0] == 'i':
        tree.insert(int(line.split()[1]))
    elif line[0] == 'f':
        print('yes' if tree.find(int(line.split()[1])) else 'no')
    elif line[0] == 'd':
        tree.delete(int(line.split()[1]))            
    else:
        tree.print()

Fixed submission:
import sys
class Tree():
    def __init__(self):
        self.root = None
    def insert(self, key):
        z = Node(key)
        y = None
        x = self.root
        while x:
            y = x
            if z.key < x.key:
                x = x.left
            else:
                x = x.right
        z.parent = y
        if y == None:
            self.root = z
        elif z.key < y.key:
            y.left = z
        else:
            y.right = z
    def find(self, key):
        x = self.root
        while x and x.key != key:
            if x.key < key:
                x = x.right
            else:
                x = x.left
        return x
    def delete(self, key):
        z = self.find(key)
        y = self.successor(z) if z.left and z.right else z
        x = y.left if y.left else y.right

        if x:
            x.parent = y.parent
        if y.parent == None:
            self.root = x 
        elif y == y.parent.left:
            y.parent.left = x
        else:
            y.parent.right = x
        if y != z:
            z.key = y.key
    def successor(self, x):
        if x.right:
            return self.minimum(x.right)
        y = x.parent
        while y and x == y.right:
            x = y
            y = y.parent
        return y

    def minimum(self, x):
        while x.left:
            x = x.left
        return x
    
    def print(self):
        print('',' '.join(map(str, self.root.inwalk())))
        print('',' '.join(map(str, self.root.prewalk())))
    
class Node():
    def __init__(self, key):
        self.key = key
        self.parent = self.left = self.right = None
    def prewalk(self):
        ret = [self.key]
        if self.left:
            ret += self.left.prewalk()
        if self.right:
            ret += self.right.prewalk()
        return ret
    def inwalk(self):
        ret = []
        if self.left:
            ret += self.left.inwalk()
        ret += [self.key]
        if self.right:
            ret += self.right.inwalk()
        return ret
tree = Tree()
n = sys.stdin.readline()
for line in sys.stdin:
    if line[0] == 'i':
        tree.insert(int(line.split()[1]))
    elif line[0] == 'f':
        print('yes' if tree.find(int(line.split()[1])) else 'no')
    elif line[0] == 'd':
        tree.delete(int(line.split()[1]))            
    else:
        tree.print()