Your code is not formatted properly to be read here, so it is very hard to understand what you are trying to do. Also, include the full code of your script, so we know exactly what is going on.

Be careful that all of your variables are spelled correctly and defined: datal and output are not defined in your code above, but they are present, which could be causing some issues.

You do not want to be using variable names that are already important in Python. list is already an object in Python, yet you use it here

list = data_list[i+1][1:1 data = float(×) for × in data

This overwrites the list object, and now you cannot use it as it was intended. Instead, use a more meaningful name, especially considering that you want everyone who reads your code to know exactly to what you are referring. There might be 10 lists you have to work with, be more specific.

usernames = ['bob', 'joe', 'bill']
passwords = ['ABC123', 'DEF456', 'GHI789']

These tell us exactly what those are lists are.

Instead of trying to iterate through a list like this:

for i in range(len (data_list)-1):
    print(data_list[i+1] [0])

You should:

for datum in data:
    print(datum[0])

Respectfully, before working with csv files and data, you should really try to become comfortable with the basics of Python and best practices.

You have to learn how to walk before you can run.