[Tutor] exercise problem
Francesco Loffredo
fal at libero.it
Fri Aug 27 18:44:28 CEST 2010
On 27/08/2010 17.05, Roelof Wobben wrote:
> Hello,
>
> My first try :
>
> def add_vectors(u, v):
> """
> >>> add_vectors([1, 0], [1, 1])
> [2, 1]
> >>> add_vectors([1, 2], [1, 4])
> [2, 6]
> >>> add_vectors([1, 2, 1], [1, 4, 3])
> [2, 6, 4]
> >>> add_vectors([11, 0, -4, 5], [2, -4, 17, 0])
> [13, -4, 13, 5]
> """
> teller=1
> getal1=0
> getal2=0
> while teller < len(u):
Up to this point, it's a good start.
Let's address the last problem first:
> uitkomst = add_vectors[u,v]
>
> But now I get this error message :
>
> uitkomst = add_vectors[u,v]
>
> TypeError: 'function' object is not subscriptable
>
> So it seems that I can't use vectors as a variable in a function.
No, it just seems that you used brackets [] instead of parentheses () in
the function call. When you call a function, you must follow its name
with parentheses, even when the function doesn't need arguments.
So this line should read:
uitkomst = add_vectors(u, v)
or, if you really (really?) think the two vectors should be enclosed in
a bigger list:
uitkomst = add_vectors([u, v]).
This is just one of the problems, I'll address the rest when you'll find
them. Just some hints:
> getal1 = getal1 + u[teller,0] + v[teller,0] ???
> getal2 = getal2 + v[teller,1] + v[teller,1] ???
> teller=teller+1
Ok, while I was writing, Walter told you about parentheses, so I'll
address your next question:
>
> But now Im getting this message :
>
>
> Traceback (most recent call last):
>
> File "C:\Users\wobben\workspace\oefeningen\src\test.py", line 28, in <module>
>
> uitkomst = add_vectors(u,v)
>
> File "C:\Users\wobben\workspace\oefeningen\src\test.py", line 17, in add_vectors
>
> getal1 = getal1 + u[teller,0] + v[teller,0]
> TypeError: list indices must be integers, not tuple
When you call add_vectors, you give it u and v as arguments, and they
are two lists, as per your requirements:
v = vector[0] makes v equal to the list [1, 0], and
u = vector[1] makes u equal to the list [1, 1].
Inside add_vectors, you want to sum the coordinates of the two vectors,
so you should refer to each of them with their position in the list.
Just as you did with the list called vector, you should use a single
integer to address an element also in the u and v lists inside
add_vectors. If you use a couple of numbers separated by a comma, as you
did, Python reads them as a tuple, and it complains. So the 2 lines that
sum the vectors should become a single one:
getal1 = getal1 + u[teller] + v[teller]
Then you don't even need to accumulate the sum in the variable getal1,
because you are building a list and you can store each sum in a
different position of the new list... remember the append method of the
lists? So that line should read:
getal1 = u[teller] + v[teller]
and getal1 should be appended to a list... uitkomst2, perhaps?
>
> Roelof
Francesco
> return uitkomst2[getal1, getal2] ???
> uitkomst= []
> vector= [[1,0], [1,1]]
> v=vector[0]
> u=vector[1]
> uitkomst = add_vectors[u,v]
>
> But now I get this error message :
>
> uitkomst = add_vectors[u,v]
>
> TypeError: 'function' object is not subscriptable
>
> So it seems that I can't use vectors as a variable in a function.
>
> Roelof
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