how to use dictionary to input in a loop?-CodePudding

I am doing programming for the last 3 months, still a beginner.

I am repeatedly getting this key error on this simple code.

m =  int(input("\n enter the total no. of elements in the structure 'N'  "))

elements = {}

for i in range(m):
        el_no = input("enter the element number:")
        el_con = input("going from which node to which node:")
        elements.update({el_no:el_con})
print('elements', elements)


def length(element):

        # find the nodes that the elements connects
        fromNode = elements[element][0]
        print('fromnode',fromNode)
        toNode = elements[element][1]
        print('fromnode',toNode)

        return fromNode, toNode
    

print(length(1))

as I run the file, I am getting this error. -

enter the total no. of elements in the structure 'N'  1

enter the element number:1

going from which node to which node:1,2
elements {'1': '1,2'}
Traceback (most recent call last):

  File "D:\python programming\a new program 2021\testing.py", line 30, in <module>
    print(length(1))

  File "D:\python programming\a new program 2021\testing.py", line 20, in length
    fromNode = elements[element][0]

KeyError: 1

CodePudding user response：

The input function returns a string, while you seem to want a tuple. So you have to convert it.

Let's say that el_con is two numbers separated by whitespace.

items = tuple(int(j) for j in el_con.split())
elements[el_no] = items

CodePudding user response：

You try to update a value for a key that is not yet in the dictionary elements. This raises the error:

elements = {}
elements.update({"joe":42})
print(elements)

NameError: name 'joe' is not defined

You may simply insert a value associated with a key. This does not depend on the previous state of the dictionary.

elements = {}
elements["joe"] = 12
elements.update({"joe":42})
print(elements)

{'joe': 42}

To my opinion the best way to deal with this is

key = "joe"
value = 42
elements[key] = value
print(elements)

If you need to increment a value in a while loop:

if key not in elements:
    elements[key] = 0
elements[key]  = 1