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!

Can you explain? Why does file.write() not work for you?

JPCosta
– JPCosta

2009-05-14 18:23:41 +00:00
Commented May 14, 2009 at 18:23 — JPCosta
– JPCosta, Commented May 14, 2009 at 18:23

John Millikin · Accepted Answer · 2009-05-14 18:30:05Z

16

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))

edited May 14, 2009 at 18:30

answered May 14, 2009 at 18:23

John Millikin

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6 Comments

SilentGhost Over a year ago

str(m) produces something different

John Millikin Over a year ago

Oh, you wrote the other solution. Yes, depending on how the output should be formatted (comma-separated, etc), manual string building might be required.

SilentGhost Over a year ago

I don't think that representation of a matrix is what OP asks for.

Jarret Hardie Over a year ago

Actually, I like seeing (and upvoted) both your solutions. I admit I also first interpreted the question the way SilentGhost did, but after reading John's solution I have to say that the question leaves the exact output format to inference.

Fry Over a year ago

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!

|

SilentGhost · Accepted Answer · 2009-05-14 18:22:43Z

11

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)

answered May 14, 2009 at 18:22

SilentGhost

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Comments

nikow · Accepted Answer · 2009-05-15 08:04:49Z

5

Why not use pickle?

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

edited May 15, 2009 at 8:04

answered May 14, 2009 at 19:27

nikow

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1 Comment

Frederick Ollinger Over a year ago

intoli.com/blog/dangerous-pickles

abhijeet · Accepted Answer · 2011-01-03 21:21:50Z

2

for row in matrix: file.write(" ".join(map(str,row))+"\n")

This works for me... and writes the output in matrix format

answered Jan 3, 2011 at 21:21

abhijeet

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Comments

russian_spy · Accepted Answer · 2010-10-18 19:52:40Z

1

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.

answered Oct 18, 2010 at 19:52

russian_spy

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