Shuffling Lists with random.shuffle()

A Random Result

Suppose a program needs one random integer from 5 through 10. The function random.randint(5, 10) can produce any integer in that interval. The result may change each time the function is called, so the important question is not which single number appears first, but which numbers are allowed to appear.

The Inclusive Endpoints

The first argument is the low boundary and the second argument is the high boundary. Both boundaries participate in the result. Therefore, random.randint(1, 6) can return 1, 2, 3, 4, 5, or 6. The function does not stop just before the high value.

Calling randint()

import random roll = random.randint(5, 10)

import random

print(random.randint(5, 10))
print(random.randint(5, 10))
print(random.randint(5, 10))

Each printed result is an integer from 5 through 10. The displayed numbers can change from run to run because the function selects a random result. Across the six possible outcomes, each number has an equal 1-in-6 chance on any individual call.

randint() and range()

randint() and range() both use a low value and a high value, but their treatment of the high value differs. random.randint(1, 6) can return 6 because randint() includes its upper endpoint. range(1, 6) excludes 6, so its sequence stops before that upper endpoint.

Random Choices in Practice

A random integer is useful when a problem can be represented by numbered choices. For example, a die-roll-style choice can use the bounds 1 and 6. A program that needs a random position can use the first and last valid position numbers as its low and high boundaries. In both cases, the task is to identify the smallest allowed integer and the largest allowed integer, then pass those two integer boundaries to randint().

import random

position = random.randint(1, 6)
print(position)

Boundary Mistakes

• Forgetting to import the random module

  The source requires the random module to be imported before calling randint().

  Fix: Begin with import random and call random.randint(low, high).

• Treating the high value as excluded

  randint() includes both its low and high endpoints.

  Fix: Include the high value when listing the possible results.

• Passing the bounds in the wrong order

  The function expects the low boundary followed by the high boundary.

  Fix: Place the smaller or low boundary first and the larger or high boundary second.

• Using non-integer arguments

  Both parameters should be integers.

  Fix: Choose integer values for both boundaries.

• Omitting a boundary

  The randint() call is described with both a low and a high parameter.

  Fix: Provide both integer boundaries.

Try It Yourself

Key Takeaways

1. random.randint(low, high) returns a random integer including both low and high.
2. random.randint(1, 6) can return six possible values: 1, 2, 3, 4, 5, and 6.
3. Unlike randint(), range() excludes its upper endpoint.
4. Import random before calling random.randint(), and provide two integer parameters in low-to-high order.
5. Use randint() when a real-world choice can be represented by an integer interval.