Python random sample with exception

Question

I'm attempting to create a sample of myList with the exception of i_.

My Attempt:

i_ = 'd'

myList = ['a','b','c','d','e']

myList = random.sample(myList, 3)

Although the above sample works fine, there is still a chance that i_ is removed from myList.

I would like to create a sample without the value of i_ being removed.

Desired Output:

Any list output containing 3 items including i_, e.g:

['a','d','e']

Answer 1

Just sample 2 values from the list without the i_ and insert i_ later:

new_list = random.sample([i for i in myList if i != i_], 2)
new_list.insert(random.randrange(0, 3), i_)

But this assumes that i_ occurs only once in your list - seems reasonable given your example but I wanted to mention this for completeness. Also I'm not sure what the desired result should be if there were multiple i_ in the list.

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You could also use a hit&miss approach that generates a sample until you get one that contains i_:

new_list = []
while i_ not in new_list:
    new_list = random.sample(myList, 3)

Note that this could be really slow if it's unlikely that i_ is drawn in the sample. For a 3-sample of 5 elements it's quite fast but it could be really slow if you draw a 3-sample from 1000 elements.

Answer 2

Guarantee that i_ will be in the list, then take one fewer random element.

myList.remove(i_)
myList = random.sample(myList, 2)
myList.append(i_)

You can combine these into one line if you wish.