Generate a random list of numbers

[Steven D'Aprano]

On Fri, 20 Nov 2015 03:05 pm, Seymore4Head wrote:

> Why does a work and b doesn't?  What I was trying to accomplish with b
> is to get a random list (of random length) that could have digits
> repeat.
> 
> I got idea for both methods from the Internet.  I do see that one uses
> brackets and the other doesn't, but I don't know the difference.
> 
> import random
> for i in range (5):
>     a = random.sample(range(10), random.randrange(3,6))
>     print a

Break it up, step by step.

range(10) produces a list from 0 to 9. random.randrange(3, 6) produces a
single integer from 3 to 5 (6 is excluded). Let's say by chance it produces
the number 4.

Then random.sample takes the list, and the integer 4, and selects 4 values
at random from the list. Say, something like this:

[8, 6, 7, 0]

Note that random.sample does NOT repeat selections. The numbers will always
be unique.



> for i in range (5):
>     b = [random.randrange (10), random.randrange(4,8)]
>     print b

As above, run through this step by step.

random.randrange(10) produces a single number at random between 0 and 9 (10
is excluded). Let's say it picks 8. 

random.randrange(4,8) produces a single number at random between 4 and 7 (8
is excluded). Let's say it picks 5.

Then b is set to the list [8, 5].

This list will always have two items.



If you want a random number of digits that might repeat:

[random.randrange(10) for i in range(random.randrange(1, 21))]

will produce a random number between 1 and 20 (21 is excluded). Let's say it
picks 6.

then range(6) produces the list [0, 1, 2, 3, 4, 5], and "for i in range..."
will iterate over those values. Although i is not used, this ends up
looping 6 times.

For each loop, random.randrange(10) produces a random digit between 0 and 9
(10 is excluded). So we end up with something like:

[6, 4, 2, 2, 6, 9]

for example.



-- 
Steven