piping input to an external script

norseman norseman at hughes.net
Tue May 12 07:16:48 CEST 2009

Tim Arnold wrote:
> Hi, I have some html files that I want to validate by using an external 
> script 'validate'. The html files need a doctype header attached before 
> validation. The files are in utf8 encoding. My code:
> ---------------
> import os,sys
> import codecs,subprocess
> HEADER = '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">'
> filename  = 'mytest.html'
> fd = codecs.open(filename,'rb',encoding='utf8')
> s = HEADER + fd.read()
> fd.close()
> p = subprocess.Popen(['validate'],
>                     stdin=subprocess.PIPE,
>                     stdout=subprocess.PIPE,
>                     stderr=subprocess.STDOUT)
> validate = p.communicate(unicode(s,encoding='utf8'))
> print validate
> ---------------
> I get lots of lines like this:
> Error at line 1, character 66:\tillegal character number 0
> etc etc.
> But I can give the command in a terminal 'cat mytest.html | validate' and 
> get reasonable output. My subprocess code must be wrong, but I could use 
> some help to see what the problem is.
> python2.5.1, freebsd6
> thanks,
> --Tim
If you search through the recent Python-List for UTF-8 things you might 
get the same understanding I have come to.

the problem is the use of python's 'print' subcommand or what ever it 
is. It 'cooks' things and someone decided that it would only handle 1/2 
of a byte (in the x'00 to x'7f' range) and ignore or send error messages 
against anything else. I guess the person doing the deciding read the 
part that says ASCII printables are in the 7 bit range and chose to 
ignore the part about the rest of the byte being undefined. That is 
undefined, not disallowed.  Means the high bit half can be used as 
wanted since it isn't already taken. Nor did whoever it was take a look 
around the computer world and realize the conflict that was going to be 
generated by using only 1/2 of a byte in a 1byte+ world.

If you can modify your code to use read and write you can bypass print 
and be OK.  Or just have python do the 'cat mytest.html | validate' for 
you. (Apply a var for html and let python accomplish the the equivalent 
of Unix's:
    for f in *.html; do cat $f | validate; done
     for f in *.html; do validate $f; done  #file name available this way

If you still have problems, take a look at os.POPEN2 (and its popen3)
Also take look at os.spawn.. et al



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