Generates balanced brackets of size n

brackets.py

# http://dl.acm.org/citation.cfm?id=357091
import random, sys

class Generator:
    def __init__(self):
        self.r = 0
        self.k = 0

    def open(self):
        print("{", end = '')
        self.r = self.r + 1
        self.k = self.k - 1

    def close(self):
        print("}", end = '')
        self.r = self.r - 1
        self.k = self.k - 1

    def probclose(self):
        return ((self.r * (self.r + self.k + 2))/(2 * self.k * (self.r + 1)))

    def gen(self, n):
        self.k = 2 * n
        self.r = 0
        while self.r != self.k:
            if self.r == 0:
                self.open()
            elif random.uniform(0, 1) < self.probclose():
                self.close()
            else:
                self.open()
        while self.k != 0:
            self.close()
        print()

x = Generator()
if len(sys.argv) < 2:
    print("first arg is # of parens")
    sys.exit()

x.gen(int(sys.argv[1]))