Python List: Why do we create two types of empty lists some times?

[sharknaut]

Hi all,

I have been struggling to understand the differences in creating a new list that some times is empty [ ] or some times it as a zero in it [0]?

---

test_list = [ ]

vs

test_list = [0]

---

Can someone please explain the rationale behind setting it to 0 or nothing?

my understanding so far is that if it is empty [ ], that means we do not want to specify any type of input for the list, and when we put a [0], then we treat it as index for later referencing or we want the list to begin at index 0?

[appylpye]

Hi @sharknaut,

How we initialize a list depends on its purpose.

If we create a list for accumulating items that meet specified criteria, we usually initialize it as an empty list, then add items that meet those criteria. Following is an example:

numbers = [2, 3, 5, 7, 9, 6, 8]
# list for numbers divisible by three
divisible_by_three = []
for number in numbers:
  if number % 3 == 0:
    divisible_by_three.append(number)
print(divisible_by_three)

Output:

[3, 9, 6]

So that we can discuss a list that we initialize with a 0 in it, please post an example of pertinent code, or provide us with a link to an exercise that offers such an example.

[sharknaut]

Thank you appylpye,

great explanation for empty list.

the [ 0 ] example one of it is in this example:
Max Num Challenge

code:

#Write your function here
def max_num(nums):
  maximum = nums[0]
  for number in nums:
    if number > maximum:
      maximum = number
  return maximum

#Uncomment the line below when your function is done
print(max_num([50, -10, 0, 75, 20]))

[stetim94]

your original question:

test_list = [ ]

# vs

test_list = [0]

should have been:

test_list = [ ]

# vs

test_list[0]

those things are very different, test_list = [] will create a new list, while test_list[0] will access the first element (at index 0) of an test_list

once a list has been defined, we can access elements in the list by index (position)

[sharknaut]

You are right, I did notice this myself just now.

Thank you for pointing it out, it makes more sense now in these exercises.