python reading wrong type

Question

I have a text file that contains lines of numbers. My program is trying to extract the lines of code and put them in a list, with each list being composed of the numbers that make up that line in the file, and then put all of these lists into one list (lets call this Triangle) and have a function applied to them, but the Python interpreter says that Triangle[x] is an integer type when I am trying to work with it, but when I ask it type(Triangle[x]), it says that it is a list. My code is below:

def compare(a,b):
"""Returns the larger of a and b"""
if a > b:
    return a
else:
    return b

doc = open('C:/Users/Joseph/My Documents/Programming fun/Python/Project Euler/18triangle.txt')

Triangle = []

for line in doc:
    Triangle.append( map( int, line.split() ) )

doc.close()

Triangle.reverse()

for i in xrange(len(Triangle) - 1):
    for j in xrange(len(Triangle[i]) - 1):              # Here it says that 'type int has no len'
        TEMP = compare(Triangle[i][j],Triangle[i][j + 1])
        Triangle[i+1] = TEMP

Thank you in advance for any advice you can offer.

What do you expect map(int, line.split()) to do exactly? Is int() a function? — Rajesh J Advani
– Rajesh J Advani, Commented Aug 17, 2012 at 22:14
It is a function, yes. That's a fairly not-uncommon line to see. — Julian
– Julian, Commented Aug 17, 2012 at 22:14
Integers don't have a length attribute. They are integers. — g.d.d.c
– g.d.d.c, Commented Aug 17, 2012 at 22:15
line.split() returns all of the numbers as a list, but since they were in a text file, they were strings. I mapped the int() function onto all of the numbers, which converts the string '57' into the integer 57, for example — jmitt
– jmitt, Commented Aug 17, 2012 at 22:15

Danica · Accepted Answer · 2012-08-17 22:24:07Z

4

This looks suspicious:

TEMP = compare(Triangle[i][j],Triangle[i][j + 1])
Triangle[i+1] = TEMP

Triangle starts out with lists of integers as members, but as you go through you're assigning elements to be integers. In fact, this happens for each element other than Triangle[0], so this will always happen as soon as i gets to 1.

By the way, this is a somewhat nicer way to read the document:

with open('C:/Users/Joseph/My Documents/Programming fun/Python/Project Euler/18triangle.txt') as doc:
    Triangle = [map(int, line.split()) for line in doc]

And your compare function is a subset of the standard max function; you could just use that instead (as pointed out by @BrendenBrown in the comments).

Also, Triangle should be triangle according to standard Python style.

edited Aug 17, 2012 at 22:24

answered Aug 17, 2012 at 22:18

Danica

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1 Comment

jmitt Over a year ago

Ah! ok, then I just need to add another index so it will be Triangle[i+1][j] = TEMP. Thank you very much.

David · Accepted Answer · 2012-08-17 22:18:26Z

1

The problem is that TEMP gets an integer, and then you put that into Triangle, so now Triangle has an element that is an integer rather than a list. Maybe you want something like

Triangle[i+1] = [TEMP]

instead of

Triangle[i+1] = TEMP

answered Aug 17, 2012 at 22:18

David

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Comments

Burhan Khalid · Accepted Answer · 2012-08-17 23:09:42Z

1

for i in xrange(len(Triangle) - 1) this is not very pythonic.

Since you want to compare two objects at once, first adjusting the list might be better. This snippet converts your list into a list of 2-tuples

>>> from itertools import izip_longest, islice
>>> x
[1, 2, 3, 4, 5]
>>> list(izip_longest(islice(x,0,None,2),islice(x,1,None,2)))
[(1, 2), (3, 4), (5, None)]

Once you have the list in that format, you can step through it like this:

for i,j in two_list:
   # rest of your loop

answered Aug 17, 2012 at 23:09

Burhan Khalid

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