Python split file into list

Question

I'm having trouble with the function below. It seems to split the file fine but then only returns it as one element

Function:

def splitRoute():
  route = []
  for line in open("route.txt","r").readlines():
    line = line.replace("\r","")
    line = line.replace("\n","")
    line = string.split(line, '>')
    route.append(line) 
  return route

Output:

[['B', 'F']]

route.txt contents:

B>F

Is it only returning one element because there is only one line in the file? I have another function that splits another file into a 7x7 list that works fine but is that only reaching all seven elements across because it has 7 lines?

Well, what else were you expecting?

Karl Knechtel
– Karl Knechtel

2012-02-20 02:41:48 +00:00
Commented Feb 20, 2012 at 2:41 — Karl Knechtel
– Karl Knechtel, Commented Feb 20, 2012 at 2:41

Blender · Accepted Answer · 2012-02-19 21:31:39Z

3

Why are you replacing newlines? Just split the string:

def splitRoute():
  route = []

  for line in open('route.txt', 'r'):
    route.append(line.strip().split('>')) 

  return route

edited Feb 19, 2012 at 21:31

answered Feb 19, 2012 at 20:00

Blender

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2 Comments

senderle Over a year ago

@Schmooo, it also creates a new copy of the list every time + is used. I'd suggest using extend instead of append; then you don't have to use sum at all.

Thomas Mitchell Over a year ago

I just realised this doesn't work if the route.txt is multiline. It takes all the lines in the file and adds it to one line in the list. I need it to split it into a 2d list so 2x3 for a three line file.

senderle · Accepted Answer · 2012-02-19 20:16:37Z

1

split creates a list. Then you append that list to another (empty) list. So the result is that you get a list inside a list. If you had more lines, you'd get a longer list of lists. Here's a quick breakdown of the code:

def splitRoute():
  route = []

You create an empty list...

  for line in open("route.txt","r").readlines():
    line = line.replace("\r","")
    line = line.replace("\n","")

For every line, you replace \r and \n characters with empty strings. Note that you could do this more easily using line.strip() ('apple\n\r'.strip() -> 'apple'). Also, you should save the file to a filename so you can close it later. Finally, you don't need to use readlines here -- just iterate over the file directly.

    line = string.split(line, '>')

Now you take the string that line refers to, split it into a list, and assign the list to line. Now line looks like this: ['B', 'F'].

    route.append(line) 
    return route

Now you've appended line to route, and route looks like this: [['B', 'F']].

If your goal is to create a single list, use extend instead of append.

def splitRoute():
  route = []
  f = open('route.txt', 'r')
  for line in f:
    route.extend(line.strip().split('>'))
  f.close()
  return route

Or, using with, and adopting a more readable indentation level:

def splitRoute():
    route = []
    with open('route.txt', 'r') as f:
        for line in f:
            route.extend(line.strip().split('>'))
    return route

Output for a file with two lines ('B>F\nF>X\n'):

>>> splitRoute()
['B', 'F', 'F', 'X']

edited Feb 19, 2012 at 20:16

answered Feb 19, 2012 at 20:00

senderle

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2 Comments

Thomas Mitchell Over a year ago

Do I need the list within a list to make it a 2D array or is there a way that this can be done with just one list?

senderle Over a year ago

If you want a 2D array, use append instead of extend. The most straightforward way to create a 2D array in Python is indeed to create a list of lists. You could also use tuples to index a dict; d = {}; d[0, 0] = 1; d[0, 1] = 0; d[1, 0] = 1; d[1, 1] = 0 and so on. But this is somewhat slower than a list of lists in most cases.

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