Python reading from file into multiple lists

Question

I don't suppose someone could point me in the right direction?

I'm a bit wondering how best to pull values out of a text file then break them up and put them back into lists at the same place as their corresponding values.

I'm sorry If this isn't clear, maybe this will make it clearer. This is the code that outputs the file:

#while loop       
with open('values', 'a') as o:
             o.write("{}, {}, {}, {}, {}, {}, {}\n".format(FirstName[currentRow],Surname[currentRow], AnotherValue[currentRow], numberA, numberB))
currentRow+1

I would like to do the opposite and take the values, formatted as above and put them back into lists at the same place. Something like:

#while loop
with open('values', 'r') as o:
             o.read("{}, {}, {}, {}, {}, {}, {}\n".format(FirstName[currentRow],Surname[currentRow], AnotherValue[currentRow], numberA, numberB))
currentRow +1

Thanks

I would highly recommend looking into the [`cvs`](http://docs.python.org/2/library/csv.html) module. That will let you write out without manually stitching your rows together and when you read it back in each row will be a list. — thegrinner, Mar 07 '14 at 14:07

score 0 · Answer 1 · answered Mar 07 '14 at 12:32

I think the best corresponding way to do it is calling split on the text read in:

FirstName[currentRow],Surname[currentRow], AnotherValue[currentRow], numberA, numberB = o.read().strip().split(", ")

There is no real equivalent of formatted input, like scanf in C.

score 0 · Answer 2 · answered Mar 07 '14 at 13:56

You should be able to do something like the following:

first_names = []
surnames = []
another_values = []
number_as = []
number_bs = []

for line in open('values', 'r'):
    fn, sn, av, na, nb = line.strip().split(',')
    first_names.append(fn)
    surnames.append(sn)
    another_values.append(av)
    number_as.append(float(na))
    number_bs.append(float(nb))

The for line in open() part iterates over each line in the file and the fn, sn, av, na, nb = line.strip().split(',') bit strips the newline \n off the end of each line and splits it on the commas.

In practice though I would probably use the CSV Module or something like Pandas which handle edge cases better. For example the above approach will break if a name or some other value has a comma in it!

score 0 · Answer 3 · answered Mar 07 '14 at 14:15

with open('values.txt', 'r') as f:
    first_names, last_names, another_values, a_values, b_values = \
    (list(tt) for tt in zip(*[l.rstrip().split(',') for l in f]))

Unless you need update, list conversion list(tt) for tt in is also unnecessary.

May use izip from itertools instead of zip.

Kei Minagawa · Answer 4 · 2014-03-07T14:25:30.420

If you are allow to decide file format, saving and loading as json format may be useful.

import json

#test data
FirstName    = range(5)
Surname      = range(5,11)
AnotherValue = range(11,16)
numberAvec   = range(16,21)
numberBvec   = range(21,26)

#save
all = [FirstName,Surname,AnotherValue,numberAvec,numberBvec]
with open("values.txt","w") as fp:
    json.dump(all,fp)

#load
with open("values.txt","r") as fp:
    FirstName,Surname,AnotherValue,numberAvec,numberBvec = json.load(fp)

values.txt:

[[0, 1, 2, 3, 4], [5, 6, 7, 8, 9, 10], [11, 12, 13, 14, 15], [16, 17, 18, 19, 20], [21, 22, 23, 24, 25]]

Python reading from file into multiple lists

4 Answers4

Linked