On Sat, Oct 6, 2012 at 1:27 PM, palmeira <palme...@gmail.com> wrote: > import struct > bloco='>%df' %(252) #Binary format > > # READ > fa=open('testIN.bin') > my_array=struct.unpack_from(bloco,fa.read()[0*4:251*4]) # my_aray = 252 > elements array > ## This read is OK! > > #WRITE > fb=open('testOUT.bin') > test=struct.pack_into(bloco,fb.write()[0*4:251*4]) # ERROR in this WRITE
You have a beautiful parallel here, but I think that's where your problem is. In the READ section, you have fa.read() which will read the whole file, and then you slice the resulting string. That's pretty inefficient for large files, but it'll work. But when you write, that completely does not work. (Even assuming you've opened read/write, per Dennis's comment.) >>> fb.write() Traceback (most recent call last): File "<pyshell#37>", line 1, in <module> fb.write() TypeError: write() takes exactly 1 argument (0 given) It needs an argument of what to write out, it doesn't return a writable buffer suitable for pack_into. I recommend you completely rewrite your file handling to use actual seeks and file writes. Also, you'll want (I think) to use binary mode on your files; character encodings don't mean much when you're working with arrays of numbers. Finally, when you post issues, "ERROR in this WRITE" isn't very helpful. Please please post the full traceback (like in my trivial example above), as problems will be much more visible. Hope that's of some value! ChrisA -- http://mail.python.org/mailman/listinfo/python-list