How does the file.seek() work ?

[gert]

On Aug 26, 12:46 am, Graham Dumpleton <graham.dumple... at gmail.com>
wrote:
> On Aug 25, 5:37 am, Tim Chase <python.l... at tim.thechases.com> wrote:
>
> > > I want the file pointer set to 100 and overwrite everything from there
> > [snip]
> > > def application(environ, response):
> > >     query=os.path.join(os.path.dirname(__file__),'teeeeeeeeeemp')
> > >     range=environ.get('HTTP_RANGE','bytes=0-').replace
> > > ('bytes=','').split(',')
> > >     offset=[]
> > >     for r in range: offset.append(r.split('-'))
> > >     with open(query,'w+') as f:
> > >          f.seek(int(offset[0][0]))
> > >          while True:
> > >              chunk=environ['wsgi.input'].read(8192).decode('latin1')
> > >              if not chunk: break
> > >              f.write(chunk)
> > >     f=open(query)
> > >     l=str(os.fstat(f.fileno()).st_size)
> > >     response('200 OK', [('Content-Type', 'text/plain'), ('Content-
> > > Length', str(len(l)))])
> > >     return [l]
>
> > A couple items of note:
>
> > - you don't open the file in binary mode -- seek is more reliable
> > in binary mode :)
>
> If my memory is right, if file is opened in binary mode, also wouldn't
> need to be decoding the WSGI input stream as latin-1 to get a string.
> Instead can just deal with bytes and write bytes to file.
>
> Graham
>
> > - if you want to lop off the rest of the file, use f.truncate()
>
> > An example:
>
> > # create the initial file
> >  >>> f = file('zzz.zzz', 'wb+')
> >  >>> f.write('abcdefghijklmnop')
> >  >>> f.close()
>
> >  >>> f = file('zzz.zzz', 'ab+')
> >  >>> f.read() # show the existing content
> > 'abcdefghijklmnop'
> >  >>> f.seek(5) # seek to the desired offset
> >  >>> f.truncate() # throw away everything after here
> >  >>> f.write('zyx') # write the new data at pos=5
> >  >>> f.close()
>
> > # demonstrate that it worked
> >  >>> f = file('zzz.zzz', 'rb')
> >  >>> f.read()
> > 'abcdezyx'
> >  >>> f.close()
>
> > > also why must I open the file a second time to know how big it is ?
>
> > Likely the output has been buffered.  You can try using
>
> >    f.flush() # write all the data to the disk first
> >    size = os.fstat(f.fileno()).st_size
>
> > which seems to do the trick for me.
> > -tkc
>

Works thanks

curl -C 10 -T upload2.wsgi http://192.168.2.17/appwsgi/wsgi/upload2.wsgi
--header "Transfer-Encoding: chunked" -v

import os

def application(environ, response):
    #query=environ.get['QUERY_STRING']
    #print (query, file=environ['wsgi.errors'])
    query=os.path.join(os.path.dirname(__file__),'teeeeeeeeeemp')
    range=environ.get('HTTP_CONTENT_RANGE','bytes 0-').replace('bytes
','').split('/')[0].split(',')
    offset=[]
    for r in range: offset.append(r.split('-'))
    with open(query,'rb+') as f:
         f.seek(int(offset[0][0]))
         if environ['REQUEST_METHOD']=='PUT':
             f.truncate()
             while True:
                 chunk=environ['wsgi.input'].read(8192)
                 if not chunk: break
                 f.write(chunk)
         f.flush()
         l=str(os.fstat(f.fileno()).st_size)
    response('200 OK', [('Content-Type', 'text/plain'), ('Content-
Length', str(len(l)))])
    return [l]