python3-numpy: Appending to a file using numpy savetxt

Question

I am trying to append data to a file using numpy's savetxt function. Below is the minimum working example

#!/usr/bin/env python3
import numpy as np
f=open('asd.dat','a')
for iind in range(4):
    a=np.random.rand(10,10)
    np.savetxt(f,a)
f.close()

The error that I got is something about the type of the error

File "/usr/lib/python3/dist-packages/numpy/lib/npyio.py", line 1073, in savetxt fh.write(asbytes(format % tuple(row) + newline)) TypeError: must be str, not bytes

This error doesn't occur in python2 so I am wondering what the issue could be. Can anyone help me out?

You have to open your file in binary instead of text mode: f=open('asd.dat','ba'). Also consider using the with statement to ensure that your file handle gets properly closed in case an error occurs. — cel
– cel, Commented Jan 5, 2015 at 19:59
Possible duplicate: stackoverflow.com/questions/14437054/…. — nwk
– nwk, Commented Jan 5, 2015 at 20:02

Community · Accepted Answer · 2017-05-23 12:02:50Z

50

You should open file by binary mode.

#!/usr/bin/env python3
import numpy as np        
f=open('asd.dat','ab')
for iind in range(4):
    a=np.random.rand(10,10)
    np.savetxt(f,a)
f.close()

reference: python - How to write a numpy array to a csv file? - Stack Overflow How to write a numpy array to a csv file?

edited May 23, 2017 at 12:02

CommunityBot

11 silver badge

answered Jan 16, 2015 at 9:23

user4352571

6094 silver badges4 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

dorien Over a year ago

Was looking a long time for this 'ba' option. Thanks.

Hyunjun Kim Over a year ago

'b' option didn't work with np.savetxt on my machine. Can anyone confirm it?

user4352571 Over a year ago

@HyunjunKim My python (python-3.5, numpy-1.13.3 on Ubuntu 16.04) work well above code. If you try string, append data type (np.savetxt(f, ["AAA"], "%s"))

Hyunjun Kim Over a year ago

@user4352571 I thought 'b' option is for writing data in unreadable format by human. But the code above doesn't work without 'b' option. Sorry for my misunderstanding.

Collectives™ on Stack Overflow

python3-numpy: Appending to a file using numpy savetxt

1 Answer 1

4 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Linked

Related