Python: `choice()` selecting the same choice -

i attempting write simple math expression generator. problem having achieving expression random numbers selected within range, , inserting random operator between each number.

here's have far:

from random import randint random import choice  lower = int(raw_input("enter lower integer constraint: ")) higher = int(raw_input("enter higher integer constraint: "))  def gen_randoms(lower, higher):     integers = list()     x in xrange(4):         rand_int = randint(lower, higher)         integers.append(rand_int)     return integers  def gen_equations(integers):     nums = map(str, integers)     print nums     operators = ['*', '+', '-']     equation = 'num op num op num op num'     equation = equation.replace('op', choice(operators))     equation = equation.replace('num', choice(nums))     print equation  nums = gen_randoms(lower, higher) gen_equations(nums) 

the problem here output repeat operator choice , random integer selection, gives 5 + 5 + 5 + 5 or 1 - 1 - 1 - 1 instead of 1 + 2 - 6 * 2. how instruct choice generate different selections?

str.replace() replaces all occurrences of first operand second operand. not treat second argument expression, however.

replace one occurrence @ time; str.replace() method takes third argument limits how many replacements made:

while 'op' in equation:     equation = equation.replace('op', choice(operators), 1) while 'num' in equation:     equation = equation.replace('num', choice(nums), 1) 

now choice() called each iteration through loop.

demo:

>>> random import choice >>> operators = ['*', '+', '-'] >>> nums = map(str, range(1, 6)) >>> equation = 'num op num op num op num op num' >>> while 'op' in equation: ...     equation = equation.replace('op', choice(operators), 1) ...  >>> while 'num' in equation: ...     equation = equation.replace('num', choice(nums), 1) ...  >>> equation '5 - 1 * 2 * 4 - 1'