writing an array to disk in python

Question

I use python basically as a calculator, from terminal interpreter. But, for a particular work, I need to write it as .py file and save its result to a file.

For my real problem, the code I came up with is:

#least.py program
import numpy as np
from scipy.optimize import curve_fit
xdata = np.array([0.1639534, 0.2411005, 0.3130353, 0.3788510,  0.4381247, 0.5373147, 0.6135673, 0.6716365, 0.7506711,  0.8000908, 0.9000000])
ydata =np.array ([7.1257999E-04,9.6610998E-04,1.1894000E-03,1.3777000E-03,1.5285000E-03,1.7297000E-03,1.8226000E-03,1.8422999E-03,1.7741000E-03,1.6574000E-03,1.1877000E-03])

def func (x,a,b,c):
    return a+b*x+c*x**3
popt, pcov =curve_fit(func,xdata,ydata,p0=(1,1,1))

and trying to write them in disk.

As from terminal, the value of popt, pcov will simply available by:

>>> popt
array([ -5.20906980e-05,   4.41458412e-03,  -3.65246935e-03])

I tried to write it in disk, appending the least.py as(as given here):

with file('3fit','w') as outfile:
    outfile.write(popt)

which gives me error:

Traceback (most recent call last):
  File "least.py", line 9, in <module>
    with file('3fit','w') as outfile:
NameError: name 'file' is not defined

Kindly help. I am in linux machine, using python 3.3

print (sys.version)
3.3.5 (default, Mar 10 2014, 03:21:31) 
[GCC 4.8.2 20140206 (prerelease)]

EDIT I would like those data in a column,as:

-5.20906980e-05   
 4.41458412e-03  
-3.65246935e-03

Is there a reason why you have to write it to a .py file -- does saving /fetching it from a binary format not work for your use case? — user559633
– user559633, Commented Mar 18, 2014 at 9:56

Christian Aichinger · Accepted Answer · 2014-03-18 09:53:27Z

5

You are using Python3, where file() is not a function any more. Use open() instead.

Furthermore, you can only write strings. So how do you want to have popt represented as a string exactly? If you want to get the same output as on the console, repr() will do:

with open('3fit', 'w') as outfile:
    outfile.write(repr(popt))

Or you could just write the numerical values, separated by blanks:

with open('3fit', 'w') as outfile:
    outfile.write(' '.join(str(val) for val in popt))

answered Mar 18, 2014 at 9:53

Christian Aichinger

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user559633 · Accepted Answer · 2014-03-18 09:54:37Z

1

This is a simple error in syntax.

You really want:

with ('3fit','w') as outfile:
    outfile.write(popt)

The with statement here is calling a context manager as mentioned in the official Python documentation.

answered Mar 18, 2014 at 9:54

user559633

Comments

Unda · Accepted Answer · 2014-03-18 09:52:48Z

0

When opening a file, you have to use the open function, 'file' doesn't exist. Modify the line as followed :

with open('3fit','w') as outfile:
    outfile.write(str(popt))

Plus, you probably can't write your np.array directly so I used the str() function.

answered Mar 18, 2014 at 9:52

Unda

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