How do I write a float list of lists to file in Python

Question

I need to write a series of matrices out to a plain text file from python. All my matricies are in float format so the simple file.write() and file.writelines()

do not work. Is there a conversion method I can employ that doesn't have me looping through all the lists (matrix = list of lists in my case) converting the individual values?

I guess I should clarify, that it needn't look like a matrix, just the associated values in an easy to parse list, as I will be reading in later. All on one line may actually make this easier, but thanks to all for your thouhts!

Answer 1

the following works for me:

with open(fname, 'w') as f:
    f.writelines(','.join(str(j) for j in i) + '\n' for i in matrix)

Answer 2

m = [[1.1, 2.1, 3.1], [4.1, 5.1, 6.1], [7.1, 8.1, 9.1]]
file.write(str(m))

If you want more control over the format of each value:

def format(value):
    return "%.3f" % value

formatted = [[format(v) for v in r] for r in m]
file.write(str(formatted))

Answer 3

Why not use pickle?

import cPickle as pickle
pckl_file = file("test.pckl", "w")
pickle.dump([1,2,3], pckl_file)
pckl_file.close()

Answer 4

import pickle

# write object to file
a = ['hello', 'world']
pickle.dump(a, open('delme.txt', 'wb'))

# read object from file
b = pickle.load(open('delme.txt', 'rb'))
print b        # ['hello', 'world']

At this point you can look at the file 'delme.txt' with vi

vi delme.txt
  1 (lp0
  2 S'hello'
  3 p1
  4 aS'world'
  5 p2
  6 a.