[Tutor] Indexing a list with nested tuples

[Alexander Quest]

Thanks Peter- I tried the replacement method where the entire tuple is
replaced with a new one and that worked. Changing the "attribute_index" (or
"selection" variable, as I called it) to an integer removed the int/str
errors.

-Alex

On Wed, Aug 3, 2011 at 12:12 AM, Peter Otten <__peter__ at web.de> wrote:

> Alexander Quest wrote:
>
> > Hi guys- I'm having a problem with a list that has nested tuples:
> >
> > attributes = [("strength", 0), ("health  ", 0), ("wisdom  ", 0),
> > ("dexterity", 0)]
> >
> > I've defined the list above with 4 items, each starting with a value of
> 0.
> > The player
> > enters how many points he or she wants to add to a given item. The
> > selection menu
> > is 1 - strength; 2 - health; 3 - wisdom; 4- dexterity. So the "selection"
> > variable is actually
> > 1 more than the index location of the intended item. So I have the
> > following code:
> >
> > print("Added ", points, "to ", attributes[selection-1][0], "attribute.")
> >
> > My intent with this is to say that I've added this many points (however
> > many) to the
> > corresponding item in the list. So if the player selects "1", then
> > selection = 1, but I subtract
> > 1 from that (selection -1) to get the index value of that item in the
> list
> > (in this case 0). Then I
> > have [0] to indicate that I want to go to the second value within that
> > first item, which is the
> > point value. I get an error saying that list indices must be integers,
> not
> > strings. I get a similar
> > error even if I just put attributes[selection][0] without the minus 1.
> >
> > Also, it seems that the tuple within the list cannot be modified
> directly,
> > so I can't add points to the original value of "0" that all 4 items start
> > with. Is there a way to keep this nested list with
> > tuples but be able to modify the point count for each item, or will it be
> > better to create a dictionary or 2 separate lists (1 for the names
> > "Strength, Health, Wisdom, Dexterity" and one
> > for their starting values "0,0,0,0")? Any suggestions/help will be
> greatly
> > appreciated!!!
>
> [I'm assuming you are using Python 3. If not replace input() with
> raw_input()]
>
> Let's investigate what happens when you enter an attribute index:
>
> >>> attribute_index = input("Choose attribute ")
> Choose attribute 2
> >>> attribute_index
> '2'
>
> Do you note the '...' around the number?
>
> >>> attribute_index -= 1
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: unsupported operand type(s) for -=: 'str' and 'int'
>
> It's actually a string, not an integer; therefore you have to convert it to
> an integer before you can do any math with it:
>
> >>> attribute_index = int(attribute_index)
> >>> attribute_index
> 2
> >>> attribute_index -= 1
> >>> attribute_index
> 1
>
> Now let's try to change the second tuple:
>
> >>> attributes = [
> ... ("strength", 0), ("health", 0), ("wisdom", 0), ("dexterity", 0)]
> >>> attributes[attribute_index]
> ('health', 0)
> >>> attributes[attribute_index][1] += 42
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: 'tuple' object does not support item assignment
>
> The error message is pretty clear, you cannot replace items of a tuple.
> You can either to switch to nested lists
>
> [["strength", 0], ["health", 0], ...]
>
> or replace the entire tuple with a new one:
>
> >>> name, value = attributes[attribute_index]
> >>> attributes[attribute_index] = name, value + 42
> >>> attributes
> [('strength', 0), ('health', 42), ('wisdom', 0), ('dexterity', 0)]
>
> However, I think the pythonic way is to use a dictionary. If you want the
> user to input numbers you need a second dictionary to translate the numbers
> into attribute names:
>
> >>> attributes = dict(attributes)
> >>> lookup = {1: "strength", 2: "health", 3: "wisdom", 4: "dexterity"}
> >>> while True:
> ...     index = input("index ")
> ...     if not index: break
> ...     amount = int(input("amount "))
> ...     name = lookup[int(index)]
> ...     attributes[name] += amount
> ...
> index 1
> amount 10
> index 2
> amount 20
> index 3
> amount 10
> index 2
> amount -100
> index
> >>> attributes
> {'dexterity': 0, 'strength': 10, 'health': -38, 'wisdom': 10}
>
> Personally I would ask for attribute names directly.
>
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