What is the difference between random.randint and randrange?

The only differences between randrange and randint that I know of are that with randrange([start], stop[, step]) you can pass a step argument and random.randrange(0, 1) will not consider the last item, while randint(0, 1) returns a choice inclusive of the last item.

So, I don't understand why randrange(0, 1) doesn't return 0 or 1. Why would I use randrange(0, 2) instead of a randrange(0, 1) which does?

Solution 1:

The docs on randrange say:

random.randrange([start], stop[, step])

Return a randomly selected element from range(start, stop, step). This is equivalent to choice(range(start, stop, step)), but doesn’t actually build a range object.

And range(start, stop) returns [start, start+step, ..., stop-1], not [start, start+step, ..., stop]. As for why... zero-based counting rules and range(n) should return n elements, I suppose. Most useful for getting a random index, I suppose.

While randint is documented as:

random.randint(a, b)

Return a random integer N such that a <= N <= b. Alias for randrange(a, b+1)

So randint is for when you have the maximum and minimum value for the random number you want.

Solution 2:

https://github.com/python/cpython/blob/.../Lib/random.py#L218

    def randint(self, a, b):
        """Return random integer in range [a, b], including both end points.
        """

        return self.randrange(a, b+1)

Solution 3:

The difference between the two of them is that randint can only be used when you know both interval limits. If you only know the first limit of the interval randint will return an error. In this case you can use randrange with only one interval and it will work. Try run the following code for filling the screen with random triangles:

import random
from tkinter import *

tk = Tk()
canvas = Canvas(tk, width=400, height=400)
canvas.pack()

def random_triangle(l1,l2,l3,l4,l5,l6):
  x1 = random.randrange(l1)
  y1 = random.randrange(l2)
  x2 = x1 + random.randrange(l3)
  y2 = y1 + random.randrange(l4)
  x3 = x2 + random.randrange(l5)
  y3 = y2 + random.randrange(l6)
  canvas.create_polygon(x1,y1,x2,y2,x3,y3)

for x in range(0, 100):
  random_triangle(300,400,200,500,400,100)

Try running again the above code with the randint function. You will see that you will get an error message.