how to remove the blank lines?

[Peter Otten]

boyeestudio wrote:

> The following program have the same function as the linux's command:tail
> -f logfile.log
> But it print a lot of blank lines while showing on the stdout.
> How to fix this problem and let it go ahead always
> showing the end line as the log file's increasing.
> 
> #tail.py:
> 
> import os
> import sys
> 
> class Tail:
>     def __init__(self,inputstream):
>         self.inputstream=inputstream
> 
>     def tail(self):
>         self.inputstream.seek(0,2)     ???Maybe this is where I'll need
> fixed,But I don't know how to....

You probably want to move to the end of the file once at the
beginning of the script, not before every attempt to read from it...

>         line=self.inputstream.readline().strip()

Don't strip() so fast. You lose the information whether you have reached the
(current) end of file or a blank line (readline() returns "" or "\n"
respectively).

>         print line
> 
> if __name__=="__main__":
>     if len(sys.argv)<=1:
>         print "You must type a log file name"
>         sys.exit()
>     arg=file(sys.argv[1],'r+')
>     while(arg):

That's always true, I think.

>         try:
>             t=Tail(arg)
>              t.tail()
>         except KeyboardInterrupt:
>             arg.close()
>             print "File closed"

A no-fluff version might be

filename = sys.argv[1]
infile = open(filename, "r")
infile.seek(0, 2)
while True:
    while True:
        line = infile.readline()
        if not line: # an empty string indicates eof 
            break 
        print line,
    time.sleep(1) # give the writing program a chance to write more lines


The inner loop can also be written

for line in iter(infile.readline, ""):
    print line,

Peter