For loop with enumerate - index position

Question

I have a solution to erase duplicates from a list. In this solution is used an enumerate.

def myfunc(list_input):
    list_output=[]
    for num1, num2 in enumerate(list_input):
        if num2 not in list_input[0:num1]:
            list_output.append(num2)
    return list_output

print(myfunc([1,1,2,3])) --> ,[1,2,3,]

However, I do not undersatand in which way we should read the index position for our enumerate.

What is the position for each interaction in list_input[0:num1] , having in consideration that we have started the for loop with a num1, num2 ?

Answer 1

Enumerate iterates over an iterable (in this cause list_input ), and with each iteration sets the first value (in this case num1 ) to the current index, and the second value (in this case num2 ) to the value of the iterable at this index.

For example, on first iteration, num1 == 0 as the iteration begins at the zeroeth element, and num2 == 1 as list_input[0] == 1 . list_input[0:num1] == [] so nothing is in it and therefore the value is appended to the outputs.

On second iteration, the index has incremented by one and so num1 == 1 . list_input[0:num1] == [1] now, and as num2 is in [1] , the value is not appended to the output list.

Answer 2

The question needs to be elaborated on, and please do fix the formatting. But if I understand correctly, if you want to remove duplicates and have a need for the positioning or index of each element (number) of the non-duplicates you make use of enumerate() and possibly do something like this:

nums = [1,1,3,5,7,9]
newlist = []
for num in nums:
  if num not in newlist:
    newlist.append(num)
for index, nums in enumerate(newlist):
  print("Index positioning: %s and Number at respective index is: %s" % (index,nums))

Output:

Index positioning: 0 and Number at respective index is: 1
Index positioning: 1 and Number at respective index is: 3
Index positioning: 2 and Number at respective index is: 5
Index positioning: 3 and Number at respective index is: 7
Index positioning: 4 and Number at respective index is: 9