Q:

new to lists on python

This is my current code:
while True:
        try:
            mylist = [0] * 7
            for x in range(7):
                    sales = float(input("Sales for day:"))
                    mylist[x] = sales
                    if  sales < 0:
                        print ("Sorry,invalid. Try again.")
        except:
            print ("Sorry, invalid. Try again.")
        else:
            break

print (mylist)

best = max(sales)
worst = min(sales)

print ("Your best day had", best, "in sales.")
print ("Your worst day had", worst, "in sales.")

When I run it I get this:
Sales for day:-5
Sorry,invalid. Try again.
Sales for day:-6
Sorry,invalid. Try again.
Sales for day:-7
Sorry,invalid. Try again.
Sales for day:-8
Sorry,invalid. Try again.
Sales for day:-9
Sorry,invalid. Try again.
Sales for day:-2
Sorry,invalid. Try again.
Sales for day:-5
Sorry,invalid. Try again.
[-5.0, -6.0, -7.0, -8.0, -9.0, -2.0, -5.0]
Traceback (most recent call last):
  File "C:/Users/Si Hong/Desktop/HuangSiHong_assign9_part.py", line 45, in <module>
    best = max(sales)
TypeError: 'float' object is not iterable

I am not quite sure how to code it so that, the lists do NOT take in negative values, because I only want values 0 or greater. 
I am not sure how to solve the TypeError issue so that the min and max values will print as in my code
My last issue is, if I want to find the average value of the seven inputs that an user puts in, how should I go about this in pulling the values out of the lists
Thank you so much

A:

Your best bet is to put the data checking into a while loop. This will keep looping over this value until your conditions are met (>0)
Also, this could get confusing for the user to figure out what day they are entering the results for. Plus you need to be using the list for the max/min, not individual values. Put it all together, and make the following changes:
        for x in range(7):
            sales=-1
            while (sales<0):
                sales = float(input("Sales for day {0}".format(x)))
                mylist[x] = sales
                if  sales < 0:
                    print ("Sorry,invalid. Try again.")

And later make this change:
best = max(my_list)
worst = min(my_list)

A:

Did you mean to say:
best = max(my_list)
worst = min(my_list)

As to the validity check, the problem there is that if the input is invalid, you still move on to the next value of x.

