Reading a list of lists from a file as list of lists in python

Question

I collected data in the form of list of lists and wrote the data into a text file. The data in the text file looks like

[[123231,2345,888754],[223467,85645]         


        

Answer 1

Make sure that:

• the file that the list data is in is a python file
• the list data is assigned to a variable
• the file is in a python module

You can then import the list from the python file. For example say that list, my_list, is in the file mylist.py

E.g:

# This is the file mylist.py
my_list = [[123231,2345,888754],[223467,85645]]

You can then treat my_list as a python list

from mylist import my_list

for item in mylist:
   print "item = <", item, ">"

Answer 2

This looks like valid JSON.

So you can simply do:

import json
with open(myfilename) as f:
    lst = json.load(f)

To store your "list of lists" in a file, do

with open(myfilename, "w") as f:
    json.dump(lst, f)

Answer 3

You could just pickle your data instead. To save it:

>>> import pickle
>>> p= [[123231,2345,888754],[223467,85645]]  
>>> with open("data.txt", "wb") as internal_filename:
...     pickle.dump(p, internal_filename)

To load it:

>>> with open("data.txt", "rb") as new_filename:
...     pp = pickle.load(new_filename)
>>> pp
[[123231, 2345, 888754], [223467, 85645]]

This is also useful for much more elaborate objects.

Answer 4

Also you can use eval to achieve this, but the other solutions maybe better:

# reading a list from a file
f = open('data.txt', 'r')
l = eval(f.read())

# storing a list to a file
outf = open('out','w')
outf.write(str(l))

Sometime using eval is a bad practice. For more information check this post.