Random number help

[MRAB]

On 2016-11-23 19:29, Chris Kaynor wrote:
> On Wed, Nov 23, 2016 at 11:17 AM, Thomas Grops via Python-list
> <python-list at python.org> wrote:
>> I need a way of generating a random number but there is a catch:
>>
>> I don't want to include certain numbers, is this possible?
>>
>> random.randint(1,100) works as it will randomly pick numbers between 1 and 100 but say i don't want 48 to come out is there a way of doing this. It needs to be an integer too so not a list unless there is a way to convert list to int
>
> There are a few ways to accomplish this, depending on the exact
> requirements. Here are some basic ideas:
> - Generate a list of all valid values, and take the one at a random
> index. random.sample may be useful. This is guaranteed to complete
> (and in only one try), but generally takes extra memory. It is also a
> reasonably easy way to sample without replacement (remove the picked
> item each time).
> - Generate a random number from the larger range, and retry if you get
> one in the invalid set. Basically akin to rolling a die, and rerolling
> until you don't get a 6. This could theoretically take forever,
> however it is often good enough in practice. This will become more and
> more inefficient as set of invalid values grows (especially if the
> invalid set is a superset of the whole range)
>
Another way is to map a shorter range to the desired numbers using an 
offset:

r = random.randint(1, 99)
if r >= 48:
     r += 1