Pick the given value and ignore non-given values in a list

Question

One of a1, a2 or a3 is given as a value while other are empty. If I want to print out only a given value, what would you like to write your code? Thank you so much in advance.

Example,

a1=empty
a2=5
a3=empty
a=[a1,a2,a3]
print(a)

a=5

Answer 1

Empty values in python are None. So maybe something like this:

a1 = None
a2 = 5
a3 = None
a = [a1,a2,a3]

def get_value(L):
    return [x for x in L if x is not None][0]

a = get_value(a)

print(a)

output:

5

Update: This could fail if there is no value in the list a, so we should include exception handling for this case:

def get_value(L):
    try:
        return [x for x in L if x is not None][0]
    except IndexError:
        return None

Answer 2

Try this:

[e for e in a if e][0]

Since non-empty values are the same as True.

You could also use:

[a.remove(None) for e in a.count(None)]
a[0]

Answer 3

Try using short-circuit property:

print(a1 or a2 or a3)

Only the one different than None will be the result.