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I have two text files that have matrices written in them(not numpy matrices, so its a list of lists). These matrices are written in string format, so the text file looks like this : [[1,2,3],[3,4,5],[6,7,8]],[[3,3,3],[5,6,7],.....

I want to read this matrix back from the text file using python. I can't read using numpy as it gives ValueError: could not convert string to float

Is there anyway to do this? Would it be easier if I just wrote the matrix as a numpy matrix in the first place(I need to change code of a previous program for that, and was just wondering if there was a python way of loading matrices when it was stored as a string in a text file)?

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  • do you have an example of the code you have tried Commented May 23, 2014 at 5:55
  • I tried numpy.load("file.txt"), but like I said that didn't work. I guess there might be a way to do it by setting custom delimiters in readline(), but how you handle the "[" and other string characters? Also, I'd prefer to use a simple method if there is one. Commented May 23, 2014 at 5:58
  • have you tried the pickle module for python? it saves python objects for you so you could just save the lists to a file then reload them. Commented May 23, 2014 at 6:05

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You could make use of the ast module:

import ast

strArray =  "[[1,2,3],[3,4,5],[6,7,8]]"

# evaluates the array in string format and converts it to a python array object
array = ast.literal_eval(strArray)

note: For multiple nested arrays like you have, literal_eval will most likely convert the string into a tuple with nested arrays as elements. Just keep that in mind as you use this module.

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