Turning a list into a list of lists Python 3

Question

I have a list file made up of car details.

e.g.

1000001 Volvo v8
1000002 Mazda 2.0

Answer 1

It sounds like you need to split each line; you can use a list comprehension, as follows

cars = [line.split() for line in open("Cars.txt")]

As mentioned in the comments; you want numerical representations of the numbers. To do this you need to convert the numerical columns into numbers. E.g.

for i in range(len(cars)):
    cars[i][0] = int(cars[i][0])
    cars[i][-1] = int(cars[i][-1])

Then e.g. cars[0][0] will be a number. Alternatively, if the numbers will always be positive integers, you can condense this to:

readline = lambda l: [int(n) if n.isdigit() else n for n in l.split()]
cars = [[ readline(line) for line in open("Cars.txt")]

For any more complicated datafile reading, you might want to use e.g. pandas.

Generators

As pointed out by zondo in the comments, you might consider using a generator instead, which doesn't load all the data into memory (instead "generating" each element when requested); this can be done by swapping [] for () in the comprehension:

cars = (line.split() for line in open("Cars.txt"))

Then you can still iterate over cars as you would a list, but you can't index into a generator, as you can a list.

Answer 2

If you want a proper way to access all the information in the text file, you can simply define a class for it. And later fill it with information from the file. Here is an example implementation. I used unpack operator (*) here.

class Car(object):

    def __init__(self, id, name, price):
        self.id = id
        self.name = name
        self.price = price

    def __str__(self):
        return self.id + ' ' + self.name + ' ' + self.price


file = open("file.txt", 'r')
cars = [Car(*line.split()) for line in file]

for c in cars:
    print c

Or use generator expression if you have a really large file

cars = (Car(*line.split()) for line in file)

In both cases it prints,

1000001 Volvo 34000
1000002 Mazda 23000

Answer 3

This is how you can store your results in a list, using the split function:

cars = []

with open("cars.txt", 'r') as f:
    for line in f:
        cars.append(line.split())

If you want to be able to search quickly based on your unique ID, you might be better off using a dictionary.

Answer 4

Here is a pure python way:

text = '1000001 Volvo 34000 1000002 Mazda 23000'

# Split text into one list
l = text.split()

# Split list into list of list every 3rd element
l = [l[i:i+3] for i in range(0, len(l), 3)]
print l

---

[['1000001', 'Volvo', '34000'], ['1000002', 'Mazda', '23000']]

Answer 5

This could be done with a regex to produce a list of tuples:

import re

text = '1000001 Volvo 34000 1000002 Mazda 23000'

l = re.findall(r'(\d+) (\w+) (\d+)', text)
print l

---

[('1000001', 'Volvo', '34000'), ('1000002', 'Mazda', '23000')]

If you really need a list of lists you can convert it:

l = [list(x) for x in l]
print l

---

[['1000001', 'Volvo', '34000'], ['1000002', 'Mazda', '23000']]