KeyError: 0 Python

Question

Hi I'm still pretty new in python and would like to know why this line:

    RP[p][t] = demand[p][t] / fillingrate[p]

is leading to the error: KeyError: 0

it follows the relevant part of the code. Is it just a mistake of notation or what's the best way to solve it?

productname = ('milk', 'yoghurt', 'buttermilk')
fillingrate = (1.5, 1.0, 2.0)

day = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)

demand = [
(5, 4, 3, 3, 4, 9, 13, 5, 4, 4, 3, 5, 10, 12),
(3, 5, 3, 5, 5, 4,  3, 4, 3, 4, 3, 4,  5,  5),
(3, 3, 5, 4, 4, 5,  4, 3, 4, 3, 4, 5,  4,  5)
]

T = range (len(day))
P = range (len(productname))


for p in P:
   for t in T:
        RP[P,T] = model.addVar (lb = 0, vtype = GRB.CONTINUOUS,
        name = 'Regular Production[' + str(p) + ',' + str(t) + ']')
        print(demand[p][t])
        print(fillingrate[p])
        RP[p][t] = demand[p][t] / fillingrate[p]
        print(RP[p][t])

You are indexing RP with [P,T], which is a tuple of ranges. Where is RP declared? Where does RP get a [0] element? — pat
– pat, Commented Oct 27, 2017 at 16:20

Ignacio Vazquez-Abrams · Accepted Answer · 2017-10-27 16:15:34Z

6

Indexing by [x, y] is absolutely not the same as indexing by [x][y]. The former results in a single dimension indexed using a tuple, whereas the latter results in a ragged 2-D array.

You will need to create a new object at the index [x] containing the values you want.

answered Oct 27, 2017 at 16:15

Ignacio Vazquez-Abrams

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Comments

Jim DeLaHunt · Accepted Answer · 2017-10-27 17:04:47Z

1

The expression P is not the same as p. In your code, the first is a range, the second is an integer from that range.

So, the expression RP[P,T] is wrong in two ways: it uses the wrong subscripts, and combines them the wrong way (as another answer points out).

I think you want RP[p][t] instead.

answered Oct 27, 2017 at 17:04

Jim DeLaHunt

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Comments

Tms91 · Accepted Answer · 2021-11-26 13:49:55Z

1

keyerror: 0 generally means that you are trying to access the value stored in a non-existing key 0 in a dictionary.

In your code it happens because, being

day = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
T = range (len(day))

you get

print(T)

range(0, 14)

so its first element is 0,
and when you run this

for p in P:
   for t in T:
        RP[P,T] = model.addVar (lb = 0, vtype = GRB.CONTINUOUS,
        name = 'Regular Production[' + str(p) + ',' + str(t) + ']')
        print(demand[p][t])
        print(fillingrate[p]) 
        RP[p][t] = demand[p][t] / fillingrate[p] 
        print(RP[p][t])

you have that the first value got by t is 0, and then at line

RP[p][t] = demand[p][t] / fillingrate[p]

when you pass that t to dictionary RP (which I guess has no key 0) a keyerror: 0 is raised.

Also, as pointed out by other questions, you should notice that

Indexing by [x, y] is absolutely not the same as indexing by [x][y]. The former results in a single dimension indexed using a tuple, whereas the latter results in a ragged 2-D array.

To help you fix your code it might be useful to know how RP is defined.

edited Nov 26, 2021 at 13:49

answered Nov 26, 2021 at 11:24

Tms91

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2 Comments

MisterMiyagi Over a year ago

demand is a list, which definitely has an index 0; it won't fail a lookup of 0 and it will never raise a KeyError. The question is about an error two lines later.

Tms91 Over a year ago

thanks, actually I pick up the wrong variable as I was writing the answer. I updated the answer.

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