large test file generator for the "balanced parens" problem

demo.txt

$ for i in {1..10}; do ./gen-test-file.py 20 ; echo ; done
[{{}{[[(){}[[][[([[][()]])(())]][{}]]][{}]]}}]
{[{{}([{{({[[(({}{{}}()))]]})[{}]}}])}()]}
{[{[[{{[]}([{({(({([])}))}{[]})}]())()}]]}[]()]}
()[({({[]({[{()}{[()]}]}[])}{}()())})[]]
[[([]{}{([([[{(([{()[([])]}])[])[]}](){}(){[]}])])}[])]]
[({{[{[][({[]({[(){()[]}][]})}{}())]}]}{}})[]]
({[]{()}(((({({[]([[[]]])()})})){()}){}[])}()[])
[(){{{[((((([[{{}}({})]{}]([{}]())[])){})))]}}({}()[])}]
[{{{}}([[]([]()({}[]()))])}]
(())()({(([(){}{}[][([])]]))})

gen-test-file.py

#!/usr/bin/env python

import sys
import random

def opposite(ch):
    if ch == '(': return ')'
    if ch == '[': return ']'
    if ch == '{': return '}'

openers = ['(', '[', '{']
closers = [')', ']', '}']

output = []
stack = []

# in first half, 75% chance of push, 25% chance pop
# in second half, reverse, until pop to zero.
early = [True, True, True, False]
late = [True, False, False, False]

n = int(sys.argv[1])

for _ in xrange(n):
    if random.choice(early):
        ch = random.choice(openers)
        output.append(ch)
        stack.append(ch)
    else:
        if len(stack) > 0:
            ch = stack.pop()
            output.append(opposite(ch))

while True:
    if random.choice(late):
        ch = random.choice(openers)
        output.append(ch)
        stack.append(ch)
    else:
        ch = stack.pop()
        output.append(opposite(ch))
        if len(stack) == 0:
            break

for ch in output:
    sys.stdout.write(ch)