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POHow to reproduce a wget-like speed interface on a linux terminal?
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copied!<p>Wget prints out speed information to stdout in a very clear manner, where the speed is shown and refreshed whilst the file is downloaded, and a bar scrolls across the screen. I'd like to replicate this sort of output, in a Python program. How is this possible?</p> <p>I thought the <a href="http://docs.python.org/library/curses.html" rel="nofollow">curses</a> library should be able to do this; this is what I came up with:-</p> <pre><code>import curses, time class Speeder( object ): """Show and refresh time and download speed in a curses interface.""" t1 = 0. # start time t = 0. # current time tf = 0. # end time def start(self, filename=None ): """Start timer""" self.t1 = self.t = time.time() curses.use_env(True) curses.initscr() self.win = curses.newwin(4, 0) if filename is not None: self.win.addnstr(filename, 50 ) self.win.refresh() def update(self, rbytes): """Refresh speed.""" t = time.time() td = t - self.t self.t = t speed = rbytes / td self.win.addstr(0,54,str('{0:.02f} B/s'.format(speed))) self.win.refresh() def end(self): """End timer""" self.tf = time.time() curses.endwin() try: speed = Speeder() speed.start(filename='foo.bar') for i in xrange(10): time.sleep(0.5) speed.update(200) finally: speed.end() </code></pre> <p>The problem is that it takes up an entire window, and I only really need a line at a time. I'd rather not push all the command line history back above the terminal window. Please correct me if I'm wrong, but I currently think curses apps always take up the entire terminal window.</p> <p>So I had a look at the <a href="http://docs.python.org/library/tty.html" rel="nofollow">tty</a> and <a href="http://docs.python.org/library/termios.html#module-termios" rel="nofollow">termios</a> modules, but I can't find any examples doing what I want to do.</p> <p>Finally, I came across <a href="http://www.mutaku.com/wp/index.php/2011/06/python-dynamically-printing-to-single-line-of-stdout/" rel="nofollow">a blog post</a> which does it by simply writing some special characters to sys.stdout. Applying his code to my Speeder class, I came up with this:-</p> <pre><code>import sys class Speeder( object ): """Show and refresh time and download speed.""" t1 = 0. # start time t = 0. # current time tf = 0. # end time def start(self, filename=None ): """Start timer""" self.t1 = self.t = time.time() if filename is not None: sys.stdout.write( '\r\x1b[K' + filename.ljust(50) ) sys.stdout.flush() def update(self, rbytes): """Refresh speed.""" t = time.time() td = t - self.t self.t = t speed = '{0} B/s'.format( rbytes / td ) sys.stdout.write( "\r\x1b[K" + speed.rjust(65) ) sys.stdout.flush() def end(self): """End timer""" self.tf = time.time() sys.stdout.write('\n') </code></pre> <p>This has fewer lines of code, which I like, but tbh I don't have a clue what's going on, or how to modify it to only update part of the line, similar to the curses.addstr function. Currently, the filename is overwritten with white-space. I could of course modify the class to construct the entire line each time from python, but I'd like to understand this in order to tailor it to my own needs.</p> <p>The author says this is possible only on VT100 terminals. So I guess this would only work on Unix terminals then? That's fine, but are there any Unix terminals that this would not work on?</p> <p>Is there better documentation on the subject, or more complicated examples (e.g. updating multiple lines, one line of many, or single characters on a line), preferably for Python? This doesn't seem like a feature of Python, but the tty, which is why I guess I've failed to find anything. Is there a man page or something I should read?</p>

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