write to specific line in file?

[castironpi]

On May 16, 5:57 pm, castironpi <castiro... at gmail.com> wrote:
> On May 16, 5:22 pm, castironpi <castiro... at gmail.com> wrote:
>
>
>
>
>
> > On May 16, 2:25 pm, 7stud <bbxx789_0... at yahoo.com> wrote:
>
> > > globalrev wrote:
> > > > i ahve a program that takes certain textsnippets out of one file and
> > > > inserts them into another.
>
> > > > problem is it jsut overwrites the first riow every time.
>
> > > > i want to insert every new piece of text into the next row.
> > > > so:
> > > > 1. how do i write to a new line every time i write to the file?
>
> > > > 2. if i dont want to write to a new line but just want to insert it
> > > > after the last token in the file, how do i do then?
>
> > > Generally, you can't "insert" anything into a file.  You can either
> > > append to the end of a file, or you can rewrite the whole file.  It
> > > sounds like you probably want to read the file into an array using
> > > readlines().  Then manipulate that array however you want--appending
> > > and inserting--and when you are done, overwrite the file with your
> > > array.
>
> > > However, you should be aware that as soon as you open a file for
> > > writing all the data is erased, and if your program should happen to
> > > crash right then, the array containing the data will disappear into
> > > the ether and your file will be empty--in other words all your data
> > > will be gone.  To prevent such an occurence, you should write your
> > > final data to another file, then delete the original file, and finally
> > > change the other file's name to the original file name.
>
> > Some options:
>
> > 1.  Limit line length.  Then offset is ( line* length ).
> > 2.  Name your relation.
> > 3.  Hijack the operating system.  Remember:
>
> > abc
> > def
>
> > on disk looks like
> > abc\ndef
>
> > where
>
> > abcd
> > def
>
> > looks like
> > abcd\ndef
>
> > So, if you want line 2, you have to scan line 1.- Hide quoted text -
>
> > - Show quoted text -
>
> You also have
>
> f.seek( X )
> f.write( 'abc' )
>
> which writes 'abc' in the middle, at offset X.
>
> f.seek( 0, SEEK_END )
>
> takes you to the back, and don't forget
>
> f.flush( ).
>
> Say you have:
>
> File:
>
> abc
> def
> ghi
>
> Symbols:
>
> 0-3
> 1-3
> 2-3
>
> abcdefghi
>
> and you want to make abc abC.  Then
>
> f.seek( 2 )
> f.write( 'C' )
>
> does work.
>
> If you want to make abc ab, then you change a different file
>
> table.seek( 0 )
> table.write( chr( 2 ) )
>
> ( or bytes( [ 2 ] ) in 3.0 ).
>
> If you want to make abc abcd, then you change both.
>
> f.seek( 9 )
> f.write( 'd' )
>
> table.seek( 0 )
> table.write( chr( 4 ) )
>
> But.  Now you have item 0 in two places.  'abc' somewhere and 'd'
> somewhere else, at 0 and at 9 respectively.  I think the file system
> overallocates room for String 1.  You would read:
>
> 0- 2- [ 3, 1 ]
>
> for 'abc'+'d'
>
> and
>
> 1- 1- [ 3 ]
> 2- 1- [ 3 ]
>
> for 'def' and 'ghi', where actual representations would be:
>
> 0- 2- [ 0/3, 9/1, 0, 0, 0, 0, 0, 0 ]
> 1- 1- [ 3/3, 0, 0, 0, 0, 0, 0, 0 ]
> 2- 1- [ 6/3, 0, 0, 0, 0, 0, 0, 0 ]
>
> As your chains start to grow, leave table 8xN, and just copy strings
> to new sectors when they become long:
>
> 0- 1- [ 9/4, 0, 0, 0, 0, 0, 0, 0 ]
> 1- 1- [ 3/3, 0, 0, 0, 0, 0, 0, 0 ]
> 2- 1- [ 6/3, 0, 0, 0, 0, 0, 0, 0 ]
>
> You can insort in linear time when you're looking for available slots.
>
> 'jklm' can't fit at 0.
>
> 0- 1- [ 9/4, 0, 0, 0, 0, 0, 0, 0 ]
> 1- 1- [ 3/3, 0, 0, 0, 0, 0, 0, 0 ]
> 2- 1- [ 6/3, 0, 0, 0, 0, 0, 0, 0 ]
> 3- 1- [ 13/4, 0, 0, 0, 0, 0, 0, 0 ]
>
> but 'nop' can.
>
> 0- 1- [ 9/4, 0, 0, 0, 0, 0, 0, 0 ]
> 1- 1- [ 3/3, 0, 0, 0, 0, 0, 0, 0 ]
> 2- 1- [ 6/3, 0, 0, 0, 0, 0, 0, 0 ]
> 3- 1- [ 13/4, 0, 0, 0, 0, 0, 0, 0 ]
> 4- 1- [ 0/3, 0, 0, 0, 0, 0, 0, 0 ]
>
> 'jklm' could've with a split:
>
> 0- 1- [ 9/4, 0, 0, 0, 0, 0, 0, 0 ]
> 1- 1- [ 3/3, 0, 0, 0, 0, 0, 0, 0 ]
> 2- 1- [ 6/3, 0, 0, 0, 0, 0, 0, 0 ]
> 3- 2- [ 0/3, 13/1, 0, 0, 0, 0, 0, 0 ]
>
> and with 'nop':
>
> 0- 1- [ 9/4, 0, 0, 0, 0, 0, 0, 0 ]
> 1- 1- [ 3/3, 0, 0, 0, 0, 0, 0, 0 ]
> 2- 1- [ 6/3, 0, 0, 0, 0, 0, 0, 0 ]
> 3- 2- [ 0/3, 13/1, 0, 0, 0, 0, 0, 0 ]
> 4- 1- [ 14/3, 0, 0, 0, 0, 0, 0, 0 ]
>
> There's an easy chance you can beat DbfilenameShelf for your
> application.- Hide quoted text -
>
> - Show quoted text -

I am still interested in this one, but doubt if anyone still reading.