Create a list of lists from text-file

Question

I'm trying to create a list of lists from a text-file. My text-file contains different categories each containing three sentences. It looks kind of like this:

Sentence 1 
Sentence 2 
Sentence 3

Sentence 1 
Sentence 2 
Sentence 3

Sentence 1... etc.

I want to read these and save each category into a list, and then make a list of those lists/categories. Unfortunally all of my attempts have failed so far, since they cant handle more than one line at a time. The blank line in between the categories is intended as a partition.

Answer 1

You can use a list comprehension:

with open('file', 'r') as f:
    data = f.readlines()
    result = [ data[i:i+3] for i in range(0,len(data),4)]

What is happening is that data contains each sentence, data[i:i+3] is a category, and I use a list comprehension to make a list of categories.

Answer 2

You can use itertools.groupby :

>>> from itertools import groupby
with open('filename') as f:
    lis = [map(str.strip, g) for k,g in 
                             groupby(f, key = lambda x : not x.strip()) if not k]
...     
>>> lis
[['Sentence 1', 'Sentence 2', 'Sentence 3'],
 ['Sentence 1', 'Sentence 2', 'Sentence 3'],
 ['Sentence 1']]

If the file is small then this is also fine:

with open('abc1') as f:
    print [map(str.strip, x.rsplit('\n'))  for x in f.read().rsplit('\n\n')]
...     
[['Sentence 1', 'Sentence 2', 'Sentence 3'],
 ['Sentence 1', 'Sentence 2', 'Sentence 3'],
 ['Sentence 1']]

Answer 3

It will be python one-liner :)

result = list(list(l for l in e.split("\n") if l) for e in open("file").read().split("\n\n"))

How it works?

open("file").read().split("\\n\\n") opens file, reads it and splits on blocks divided by double-enter.

list(l for l in e.split("\\n") if l) splits one block (named as e ) to lines and makes list from it. if l is used to eliminate empty lines, if you'd used more than two enters or have got empty lasy line.

The last thing is to connect it - result = list( expression_2 for e in expression_1) - We just use expression_2 on every block from expression_1 and make list from them. Simply and in one line :)