def buy_sell_hold(*args):
    cols = [c for c in args]
    requirement = 0.02
    for col in cols:
        if col > requirement:
            return 1
        if col < -requirement:
            return -1
    return 0

  df['{}_target'.format(ticker)] = list(map( buy_sell_hold,
                                               df['{}_1d'.format(ticker)],
                                               df['{}_2d'.format(ticker)],
                                               df['{}_3d'.format(ticker)],
                                               df['{}_4d'.format(ticker)],
                                               df['{}_5d'.format(ticker)],
                                               df['{}_6d'.format(ticker)],
                                               df['{}_7d'.format(ticker)] ))

1. cols = [c for c in args]

First, we need to understand what args are. Args are special, and come from the *args parm of this helper function. *args let us pass an indeterminate # of arguments to a function. *kwargs is the other option, which lets us pass keyword args.

You can learn more about args and kwargs here: https://pythonprogramming.net/args-kwargs-intermediate-python-tutorial/

Then the whole [c for c in args] is list comprehension. You can use list comprehension to either do something in a short for loop on one line, or you can use it to create an actual list. In our case, we're creating a list. We also could just skip the creation of the list in the first place, and just iterate over the args. I made the list since I wanted to leave more options open for this function, but it wound up not being totally necessary.

You can learn more about list comprehension here: https://pythonprogramming.net/list-comprehension-generators-intermediate-python-tutorial/


2.  A more general question.  For each ticker passed in does the function make the buy/sell label determination based on the first value it finds that is > .02 / < -.02?

Yes.

This is because a return is breaking/exiting for a function, so once a return statement is reached, that's it for the function.

There are other types of blocks of code you can write that, rather than a single return, can produce streams of returns, called generators, and generators are introduced in that tutorial linked above (https://pythonprogramming.net/list-comprehension-generators-intermediate-python-tutorial/), and continue to part 5, then are further explained in part 9: https://pythonprogramming.net/more-generators-intermediate-python-tutorial/

Hope all this helps!