#264 Picker - The Python Way

Using a lotto picker example to demonstrate random numbers and set operations the python way

Notes

Picking numbers for a lottery is a simple demonstration of two language features:

random number generation
producing a unique set

This is a little demonstration of how to do this the python way.

Random Number Generation

The random standard library provides a pseudo-random number generator (PRNG), currently implemented as a Mersenne Twister with a period of 2**19937-1.

The random.randint(a, b) function return a random integer N such that a <= N <= b.

random.randint(1, 10)
 => 6

Unique Sets

We need to pick a unique set of numbers i.e. no repeats. There are many ways of doing this. Since we are picking from a continuous series, we can simplify things by just ensuring that the results set does is unique i.e. does not contain an repeating elements.

This is perfect use of the set library type. The set class provides collection of unordered values with no duplicates.

my_numbers = set()
 => {}
my_numbers.add(5)
 => {5}
my_numbers.add(5)
 => {5}

The Example

See lpickr.py. The core routine uses randint for random number generation and set for unique result set

def pick(number_count, upper_limit):
    if number_count > upper_limit:
        raise Exception('Upper limit must be >= the number to pick')

    random.seed()

    choices = set()
    while len(choices) < number_count:
        choices.add(random.randint(1, upper_limit))

    return sorted(list(choices))

Using the Example

The lpickr.py script supports a simple command line to pick “n” numbers from 1 to a max number “m”

Call for instructions:

$ ./lpickr.py ?
Usage: python ./lpickr.py <number_to_pick> <max>
e.g:

    python ./lpickr.py 6 40
    5, 6, 14, 28, 30, 38

Some sample runs:

$ ./lpickr.py 3 10
1, 6, 7
$ ./lpickr.py 3 10
1, 8, 10
$ ./lpickr.py 3 10
1, 4, 9
$ ./lpickr.py 3 10
1, 5, 7
$ ./lpickr.py 7 49
8, 16, 20, 29, 43, 46, 49

Running the Tests

Some basic tests are included in test_lpickr.py

$ ./test_lpickr.py
....
----------------------------------------------------------------------
Ran 4 tests in 0.035s

OK

Project Notes