Why do I require an "elif" statement here?

[Jim]

Tim Chase wrote:
> > Could somebody tell me why I need the "elif char == '\n'" in
> > the following code?
> >
> > This is required in order the pick up lines with just spaces
> > in them.
> > Why doesn't the "else:" statement pick this up?
>
> Following through with the below code:
>
> if the line consists of only a newline, it gets ignored due to
> the "if line[0] == whitespace" line. However, if the line
> consists of only whitespace followed by a newline you *do*
> successfully get to the "else" in question. There's no other
> place for you to go.
>
> However, what happens then? If you fall into you the top half of
> your "if x > 0 ..." statement:
>
> you strip **all** *true* whitespace from the line with your
> lstrip() call. Since there's nothing between your "whitespace"
> (simple spaces) and the \n, the \n gets swallowed by the lstrip()
> call. Thus, you output.write() an empty string.
>
> I recommend a few judiciously placed "print repr(thing)" lines as
> you try to debug to see where things aren't what you expect them
> to be.
>
> As another sidelight, rather than using the "i=0, i+= 1" aspect,
> you can use the more pythonic idiom of
>
> 	for i, char in enumerate(line):
>
> (taking into consideration that i becomes zero-based).  This will
> automatically update "i" on each pass.
>
> -tkc
>
> >
> > OLD_INDENT = 5  # spaces
> > NEW_INDENT = 4  # spaces
> >
> > print 'Reindent.py:'
> > print '\nFrom file %s' % infile
> > print 'Change %i space indentation to %i space indentation.' % (
> >                                          OLD_INDENT, NEW_INDENT)
> > print 'And place revised file into %s' % outfile
> >
> > whitespace = ' '
> > n = 0
> > nline = 0
> >
> > for line in input.readlines():
> >     nline += 1
> >     # Only look at lines that start with a space.
> >     if line[0] == whitespace:
> >         i = 0
> >         for char in line:
> >             i += 1
> >             if char == whitespace:
> >                 pass
> >             elif char == '\n':          # Why do I need this for a
> > blank line with only spaces?
> >                 output.write(line)
> >                 break
> >             else:                        # Why doesn't the blank line
> > get picked up here?
> >                 x = line.count(whitespace*OLD_INDENT,0,i)
> >                 # Reindent lines that have exactly a multiple of
> > OLD_INDENT.
> >                 if x > 0 and (i-1)%OLD_INDENT == 0:
> >                     output.write(whitespace*NEW_INDENT*x+line.lstrip())
> >                     n += 1
> >                     break
> >                 else:
> >                     output.write(line)
> >                     break
> >     else:
> >         output.write(line)
> >
> > input.close()
> > output.close()
> > print 'Total number of %i lines reindented out of %i lines.' % (n,
> > nline)
> >

Thank you Tim.
Hard to believe that lstrip() produces an empty string on lines with
just spaces and doesn't remove the '\n'  with lines that have
characters.
I'm now using all your suggestions, even "print repr(thing)" which I
wasn't aware of.
Thanks,
Jim