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Python Python Collections (2016, retired 2019) Lists Shopping List Take Three

Youssef Moustahib
Youssef Moustahib
7,779 Points
Posted by Youssef Moustahib
Youssef Moustahib
7,779 Points

Can you fix my code?

So I tried to do the new style of shopping list slightly different from Kenneth's. The problem I am having is follows:

1) When I add a new item (anything after my first added item) it prompts me to know where I would like to put it, if I press enter to send it to the back of the list, it does not append to the list.

2) The insert method works, once I am prompted for a position, I will give it position 1 for example, but it won't move to position 1? it will be 2nd in the list.

Here is my code, please look at "test1.py":

https://w.trhou.se/8i8ebtrfuy

Thank you!

2 Answers

Steven Parker
Steven Parker
229,744 Points
Steven Parker
Steven Parker
229,744 Points
  1. When you don't enter a value, an exception occurs during the attempt to convert it into a number. The exception code sets "position" to 0 but never adds the item to the list.
  2. The number given to "insert" is not the number to insert at, but to insert after. The code you have in "shoppinglist3.py" handles this correctly by subtracting one from the value, but "test1.py" doesn't do that.
Youssef Moustahib
Youssef Moustahib
7,779 Points
Youssef Moustahib
Youssef Moustahib
7,779 Points

Hi Steven Parker,

1) If it sets it to "0" then shouldn't it append it to the start of the list then?

2) Could you please breakdown why position -1 appends it to the right place?

Jennifer Nordell Please also take a look if you have time, thanks

Steven Parker
Steven Parker
229,744 Points
Steven Parker
Steven Parker
229,744 Points
  1. The exception code sets the "position", but then it never does an "append" or an "insert" — as the code is now, those are only done in the "else" conditions.
  2. Another (and more common) way to think about the argument to "insert" is that inserts in front of the item based on index number. And index numbers start at 0 instead of 1. So if you count your positions starting from 1 you nust subtract one to get the index number.