argument of type 'int' is not iterable Issue

What I trying to do is picking random integers from a value, for example: 1:32 will be an input, I will split by the : and then select a random value. Then Selenium will select the dropdown based on what value is returned.

My code:

# SELECT
if register_parts[3] == "SELECT":
    if register_parts[0] + '="' + register_parts[1] + '"' in self.driver.page_source:
        _select_value = ""
        if ":" in register_parts[2]:
            _select_value = self.get_random_value_between(register_parts[2]) 
            _select = Select(selenium_action)
            _select.select_by_visible_text(_select_value)
            self.write_to_debug_file("self.select_by_visible_text(" + _select_value + ") --> SELECT --> [ " + _select_value + " ]")
        else: 
            _select_value = register_parts[2]
            _select = Select(selenium_action)
            _select.select_by_visible_text(_select_value)
            self.write_to_debug_file("self.select_by_visible_text(" + _select_value + ") --> SELECT --> [ " + _select_value + " ]")

Additional function:

def get_random_value_between(self, input_values):
    ''' this function will return a random value between: x:x or 1:31 for example ... '''
    parts = input_values.split(':')
    return random.randrange(int(parts[0]), int(parts[1]))

The problem is on this line:

_select.select_by_visible_text(_select_value)

I'm getting the error:

argument of type 'int' is not iterable

From reading up, I think the issue lies in the fact I am doing:

if ":" in

I could be wrong. I'm not sure how to fix it. Any help on the issue would be appreciated. As far as I can see, the code should work, but I must be missing something. I have read a few threads on here regarding the error but it's still not sinking totally in.