Python print语句不带回车符

Question

I'm trying to write a simple tool that reads files from disc, does some image processing, and returns the result of the algorithm. Since the program can sometimes take awhile, I like to have a progress bar so I know where it is in the program. And since I don't like to clutter up my command line and I'm on a Unix platform, I wanted to use the '\\r' character to print the progress bar on only one line.

But when I have this code here, it prints nothing.

# Files is a list with the filenames
for i, f in enumerate(files):
    print '\r%d / %d' % (i, len(files)),
    # Code that takes a long time

I have also tried:

print '\r', i, '/', len(files),

Now just to make sure this worked in python, I tried this:

heartbeat = 1
while True:
    print '\rHello, world', heartbeat,
    heartbeat += 1

This code works perfectly. What's going on? My understanding of carriage returns on Linux was that it would just move the line feed character to the beginning and then I could overwrite old text that was written previously, as long as I don't print a newline anywhere. This doesn't seem to be happening though.

Also, is there a better way to display a progress bar in a command line than what I'm current trying to do?

Answer 1

Try adding sys.stdout.flush() after the print statement. It's possible that print isn't flushing the output until it writes a newline, which doesn't happen here.

Answer 2

Handling of carriage returns in Linux differs greatly between terminal-emulators.

Normally, one would use terminal escape codes that would tell the terminal emulator to move the virtual "carriage" around the screen (think full-screen programs running over BBS lines). The ones I'm aware of are the VT100 escape codes:

\\e[A : up
\\e[B : down
\\e[C : right
\\e[D : left
\\e[1~ : home
\\e[4~ : end

Where \\e is the escape character, \\x1b .

Try replacing all \\r 's with \\e[1~

Also see this post

Answer 3

如果您的终端是行缓冲的，如果您不发出换行符，则可能需要sys.stdout.flush()才能看到您的打印。