Python script to create random (huge) expressions

rnd_expr.py

#!/usr/bin/env python
#
# Copyright (C) 2016 Heiko Schaefer <heiko@rangun.de>
#
#    This work is free. You can redistribute it and/or modify it under the
#    terms of the Do What The Fuck You Want To Public License, Version 2,
#    as published by Sam Hocevar. See http://www.wtfpl.net/ for more details.
#

import ast
import sys
import random
import itertools
import operator as op

def gen_digit(n):

	digit = ""

	if random.randint(0, 1e06) % 17 == 0: digit += "-"

	return digit + str(random.randint(pow(10, n - 1), pow(10, n) - 1));

def rnd_op():
	ops = [ "+", "-", "*", "/" ]
	return ops[random.randint(0, 3)]

def eval_(node):

	operators = {ast.Add: op.add, ast.Sub: op.sub, ast.Mult: op.mul,
             ast.Div: op.truediv, ast.Mod: op.mod, ast.USub: op.neg}

	if isinstance(node, ast.Num): return node.n
	elif isinstance(node, ast.BinOp):
		return operators[type(node.op)](eval_(node.left), eval_(node.right))
	elif isinstance(node, ast.UnaryOp):
		return operators[type(node.op)](eval_(node.operand))
	else: raise TypeError(node)

def right_op(op, expr):

	if op == "/":

		try: v = eval_(ast.parse(expr, mode='eval').body)
		except ZeroDivisionError: v = 0

		if v == 0: return op + " (" + expr + " + " + gen_digit(random.randint(1, 4)) + ")"

	return op + " " + expr

def gen_term():

	term = ""

	if random.randint(0, 1e06) % 17 == 0: term += "-"

	return term + "(" + right_op(gen_digit(random.randint(1, 4)), \
			right_op(rnd_op() + " " + gen_digit(random.randint(1, 4)), \
			rnd_op() + " " + gen_digit(random.randint(1, 4)))) + ")"

def build_expr(): return "(" + gen_term() + " " + right_op(rnd_op(), gen_term()) + \
			" " + right_op(rnd_op(), gen_term()) + ")"

def rnd_expr(m):

	sys.stdout.write(build_expr())
	sys.stdout.flush()

	for _ in itertools.repeat(None, m): 
		sys.stdout.write(" " + right_op(rnd_op(), build_expr()))
		sys.stdout.flush()

	sys.stdout.write("\n")
	sys.stdout.flush()

if len(sys.argv) > 1: rnd_expr(int(sys.argv[1]))
else: rnd_expr(0)