CODEWITHSUNDEEP
pythonlistiteration
Sean
Sean

Reputation: 1313

Python list iteration

So i have a list of heights:

heights = [1, 2, 3, 5, 7, 8, 8, 13]

And im using this function to store each height integer value and its index in the list in a class i called Node.

def initializeNodes(heights):
    ans = []
    for height in heights:
        ans.append(Node(heights.index(height), height))
    return ans

But my problem is, because their are two 8's in the list, its giving them both the same first 8 position of 5 in the list:

0 1
1 2
2 3
3 5
4 7
5 8
5 8
7 13

How can i go around this? Thanks!

Upvotes: 2

Views: 104

Answers (3)

mbdavis
mbdavis

Reputation: 4020

The problem is that you're generating the index from the values, why not do it the other way around? 

heights = [1, 2, 3, 5, 7, 8, 8, 13]

def initializeNodes(heights):
    ans = []
    for index in range(len(heights)):
        ans.append(Node(index, heights[index]))
    return ans

This creates a list from 0 to the length of heights, and then will append the index then the height at this index.

Upvotes: 0

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 251186

The problem with list.index is that it'll only return the index of first occurrence of the item.

>>> heights = [1, 2, 2, 3, 5, 5, 7, 8, 8, 13]
>>> heights.index(2)
1
>>> heights.index(5)
4
>>> heights.index(8)
7

help on list.index:

L.index(value, [start, [stop]]) -> integer -- return first index of value.

You can do provide a different start value to list.index than 0, to get the index of repeated items:

>>> heights.index(5,heights.index(5)+1) #returns the index of second 5
5

But that is very cumbersome, a better solution as @MartijnPieters already mentioned is enumerate

Upvotes: 1

Martijn Pieters
Martijn Pieters

Reputation: 1125258

Use enumerate() to generate an index:

def initializeNodes(heights):
    ans = []
    for i, height in enumerate(heights):
        ans.append(Node(i, height))
    return ans

You can collapse the four lines into 1 using a list comprehension:

def initializeNodes(heights):
    return [Node(i, height) for i, height in enumerate(heights)]

Upvotes: 6

Related Questions