list index out of range through an array

Question

I'm not sure what's wrong. I assume I have surpassed an array limit perhaps.

    def lcs(arr):
      if len(arr) == 0:   # arr of length 0
        return
      sumarr = []
      counter = 0
      sum = 0
      for i in arr:
        if arr[i] > 0:
          sum = sum + arr[i]
        if arr[i] < 0:
          sumarr[counter] = sum
          counter += 1
      print max(sumarr)

The error I get is:

      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
        File "<stdin>", line 8, in lcs
      IndexError: list index out of range

#

I've modded the code a bit

      def lcs(arr):
        if len(arr) == 0:   # arr of length 0
          return
        sumarr = []
        counter = 0
        sum = 0
        for i in arr:
          if i > 0:
            sum = sum + i
          if i < 0:
            sumarr[counter] = sum
            counter += 1
        print max(sumarr)

However I'm getting this error

      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
        File "<stdin>", line 13, in lcs
      ValueError: max() arg is an empty sequence

I thought I was constantly updating my sumarr[]. How come the error is telling me that I am passing an empty list into max()?

shx2 · Accepted Answer · 2013-08-10 13:02:31Z

1

When you do for i in arr, i gets the elements of the array (one at a time), not their indices. What you want in your example is to replace each arr[i] with i.

answered Aug 10, 2013 at 13:02

shx2

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4d4c · Accepted Answer · 2013-08-10 13:03:06Z

1

Use enumerate to go point to right position of the array:

   def lcs(arr):
      if len(arr) == 0:   # arr of length 0
        return
      sumarr = []
      counter = 0
      sum = 0
      for count, i in enumerate(arr):
        if arr[count] > 0:
          sum = sum + arr[i]
        if arr[count] < 0:
          sumarr[counter] = sum
          counter += 1
      print max(sumarr)

answered Aug 10, 2013 at 13:03

4d4c

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1 Comment

shx2 Over a year ago

What's the point of using enumerate if the count variable is not used? (should have i instead of arr[count])

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