Hi Aditya,
I think the issue here is that you don't do anything to specify what folder you are writing "sas111.txt" in.  For instance, on the Mac if you start Chimera by double-clicking then the "current folder" is /, which you almost certainly don't have write permission for.  So instead of opening just "sas111.txt" you need to specify the full path to the file, e.g.:

out = open("/Users/aditya/sas111.txt", "a")

Along the same lines, this code will always write sas111.txt in your home folder:

from os import expanduser
out = open(expanduser("~/sas111.txt"), "a")

--Eric

                        Eric Pettersen
                        UCSF Computer Graphics Lab
                        http://www.cgl.ucsf.edu

On Jan 28, 2011, at 4:04 AM, Aditya Padhi wrote:

Hi Elaine,
    Hope you are fine. If you remember I was calculating per residue SASA using Chimera for my MD simulated protein. At that time it was working fine. But I did some more simulation run and now I want to calculate SASA for the entire trajectory but unfortunately Its showing the following error.

Error
Problem in per-frame script:
IOError: [Errno 13] Permission denied: 'sas111.txt'

  File "<string>", line 3, in <module>

See reply log for Python traceback.

For your reference, I am giving the script also. It was working fine previously but with the same procedure which I followed this script is not working and showing the above mentioned error.

Script

from chimera import openModels, Molecule

out = open("sas111.txt", "a")
x='---------------------------------------------------------------------------------'
for m in openModels.list(modelTypes=[Molecule]):
    for r in m.residues:
        try:
            sas = r.areaSAS
        except AttributeError:
            continue
        print>>out, r, sas
print>>out,x
out.close()


Kindly help me.
Thank you.
Aditya.
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