[Tutor] problem with back slash

[Alan Gauld]

On 23/02/2022 19:37, Alex Kleider wrote:
> I've written myself a little utility that accepts a text file which
> might have very long lines and returns a file with the same text but
> (as much as possible) with the lines no longer than MAX_LEN
> characters. (I've chosen 70.)
> It seems to work except when the the source file contains back
> slashes! (Presence of a back slash appears to cause the program
> to go into an endless loop.)
> I've tried converting to raw strings but to no avail.
> 
> Here's the code, followed by an example source file.
> 
> '''
> #!/usr/bin/env python3
> # file: limit_line_length.py
> """
> Accepts a text file and tries to shorten lines to MAX characters.
> First parameter must be a file name.
> Optional second parameter can be the output file's name.
> If 2nd param is not specified, output will go to "new_<1stParam>".
> """
> 
> import sys
> 
> MAX = 70
> 
> 
> def split_on_space_closest_to_max_len(line, max_len=MAX):
>     """
>     Returns a tuple of two (possibly empty) strings.
>     If the line is <= <max_len>: it is returned as t[0] & t[1] as ''.
>     If indented beyond <max_len> t[0] as '' & t[1] as line[max_len:]
>     If there are no spaces then t[0] as <line> and t[1] as ''.
>     If the first space is beyond <max_len>: t[0] is what is up to the
>     space and t[1] what was after the space.
>     Otherwise t[0] is the longest it can be up to max_len up to a
>     space and t[1] is what comes after the space.
>     Trailing spaces are stripped.
>     """
>     line = line.rstrip()
>     line_length = len(line)
>     if line_length <= max_len:  # simplest scenario
>         return (line, '')       # empty lines included
>     original_line = line[:]
>     unindented_line = line.lstrip()
>     n_leading_spaces = line_length - len(unindented_line)
>     if n_leading_spaces > max_len:  # big indentation!!!
>         return ('', line[max_len:])
>     indentation = ' ' * n_leading_spaces
>     max_len -= n_leading_spaces
>     i_last_space = unindented_line.rfind(' ')
>     if i_last_space == -1:  # no spaces on which to split
>         return (line, '')
>     i_space = unindented_line.find(' ')
>     if i_space > max_len:
>         return (indentation + unindented_line[:i_space],
>                 unindented_line[i_space+1])

Missing colon on that line? See below for comparison...

>     while True:
>         next_space = unindented_line.find(' ', i_space+1)
>         if next_space > max_len: break
>         else: i_space =next_space

I think this loop could be replaced with a rfind()
on a slice upto max_space?

>     return (indentation + unindented_line[:i_space],
>             unindented_line[i_space +1:])

But I doubt that's the cause of the backslash issue.
And I have no idea what is. :-(

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
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