Problems with sys.stout.flush()

[Joel Ross]

Carl Banks wrote:
> On May 23, 2:20 am, Joel Ross <jo... at cognyx.com> wrote:
>> Carl Banks wrote:
>>> On May 22, 10:33 pm, Joel Ross <jo... at cognyx.com> wrote:
>>>> Hi all,
>>>> I'm using python 2.5 and trying to flush the sys.stout buffer with
>>>> sys.stout.flush(), but doesn't seem to work. Each time a line is printed
>>>>    it appends the one before it I need to clear the output and write a
>>>> new output without appending the previous one.
>>> That's not how streams work, chief.  Once you output (and flush)
>>> something you can't un-output it.
>>> What you probably want to do is to write a carriage return ("\r")
>>> which usually causes the cursor to return to the beginning of the
>>> line, so that any new text you write overwrites the old text.
>>> This has nothing to do with flushing; flushing doesn't erase or clear
>>> the old input.  Flushing is usually needed for a different reason,
>>> however, namely standard output doesn't actually get sent to the
>>> console until it sees a newline ("\n") unless you flush the buffer.
>>> Try to adapt this example to your problem:
>>> for i in xrange(11):
>>>     sys.stdout.write('*'*(10-i) + ' '*i + '\r')
>>>     sys.stdout.flush()
>>>     time.sleep(2)
>> Your example prints a new line each time,
> 
> Did you run it and observe what happened, or did you just guess what
> it actually did?  On my system it doesn't print new lines.
> 
> 
>> Doesn't help me with a
>> progress bar, do you know of anyway doing it with the print command? My
>> progress bars works fine this is the only problem im having with it at
>> the moment. any help would be appreciated.
> 
> Well, based on the code you posted it doesn't look like your progress
> bar is fine.
> 
> Anyway, you haven't described the problem you are having very well,
> and we can guess what might be wrong but if you want better help
> you're going to have to describe your problem more coherently.  Give
> us the
> 
> 1. What code are you actually running (cut-and-paste, please, don't
> retype).
> 2. What do you expect the code to output (type in actual output you
> expect to see, not merely a description).
> 3. What does the code actually output when you run it (cut-and paste,
> please, don't just describe).
> 4. Include any tracebacks if there are any.
> 
> In the meantime, I repeat my suggestion that you take my example and
> adapt it to what you are doing.
> 
> One other note: the print statement is unsuitable for this task
> because it always prints a trailing whitespace.  Use sys.stdout.write
> for it.
> 
> 
> Carl Banks
Hey,

The only reason I didn't supply full details is because I thought it may 
just be something simple I was missing. Sorry for the confusing. Well 
here's the full code.

import sys, os
from time import sleep


class progress:

     def progressbar(self, number, total,  char):

         percentage = float(number*100)/total
         percentage = int(round(percentage))
         percentage = int(100 - percentage)
         self.f=sys.stdout
         if percentage > 0:
             char = char * percentage
             self.f.write(char)
             self.f.flush()      	
             sleep(0.2)


     def countlines(self, file):

         lineCount = 0
         f = open(file)
         it = iter(f)
         try:
             while it.next():
                 lineCount += 1
         except StopIteration:
                     pass
         return lineCount


def main():

     p = progress()
     lines = 5
     #lines = p.countlines("/tmp/junk")
     count = lines
     for i in xrange(lines):
         p.progressbar(count, lines, "*")
         count -=1
     print "Finished"

if __name__ == "__main__":
         main()

For now we can ignore the countlines() function. I need a nice progress 
display e.g. ********************** continuing on til it reaches 100% I 
need this to print out on one line only. At the moment it does do this, 
only problem is its appends the print out from the last print out. I 
need it to clear the last print out and then print the new print out 
without appending the last.

So when it prints a progress at 50% it will print 50 (*) characters and 
if the next progress is 51% it will print 51 (*) characters including 
the last 50 (*) characters, so instead on ending up with 100 (*) 
characters I end up with a shit load of them depending on how many lines 
I pass to the progressbar() function.

Needed Output:
***************************************************************************************************Finished


Current Output:
********************************************************************************************************************************************************************************************************Finished

Note: As you can see I'm only sending 5 lines to the progressbar() 
function and It prints this many characters, so you could imagine if I 
have 10000 lines I would end up with a heap of * characters.

Regards
jross