When defining a python class, how to set a random variable in it?

Question

Say I have a class called Person, which will have only the person's name and gender.

The gender should be randomly selected from Male and Female. To do that, I import the random.randint() function. The random gender is determined according to the random int.

import random

class Person:
    alias = random.randint(1, 3)
    if alias == 2:
        gender = 'Male'
    else:
        gender = 'Female'

    def __init__(self, name):
        self.name = name

r = Person('rachel')
s = Person('Stanky')
print(r.gender)
print(s.gender)

However, the result I get for different person from this class all have the same gender. My understanding is the randint is fixed once been generated. My question is how to make it different for each class instance.

Answer 1

The reason your never getting a different gender is because the gender attribute is a class variable. Once Python creates your class object Person, the value of gender is never computed again. You need to make the gender variable an instance attribute. That means the gender will be computed on a per instance basis, instead of per class definition. eg:

import random

class Person:
  def __init__(self, name):
      self.name = name
      alias= random.randint(1, 3)
      if alias == 2:
          self.gender = 'Male'
      else:
          self.gender = 'Female'

r= Person('rachel')
s= Person('Stanky')

print(r.gender) 
print(s.gender)

Which outputs

Female
Male

On a side note, I think a much better choice for your task would be to use random.choice() to select a random gender from a list of genders(male or female):

from random import choice

class Person:
  genders = ('Male', 'Female', 'Female')
  def __init__(self, name):
      self.name = name
      self.gender = choice(Person.genders)

rachel = Person('Rachel')
stanky = Person('Stanky')

print(rachel.gender) 
print(stanky.gender)

Notice in my example above, Person.genders is a class variable. This is on purpose. Because we only need to create a list of genders once, we can make the list a class level variable.

Answer 2

It seems you already guessed the reason correctly why the gender doesn't change. To solve this you could use a property for gender:

import random

class Person(object):
    def __init__(self, name):
        self.name = name

    @property
    def gender(self):
        try:
            # If it has been defined for the instance, simply return the gender
            return self._gender
        except AttributeError:
            # If it's not defined yet, define it, and then return it
            self._gender = random.choice(['male', 'female'])
            return self._gender

r = Person('rachel')
s = Person('Stanky')
print(r.gender)
print(s.gender)