I've just learnt that to clear a line that you printed in Python, do this:
sys.stdout.write('\x1b[2K')
Why is it so complicated? what does that weird code mean? and is there any alternative in print command?
Print does offer "end" option that allows to go back and forth in lines, but no way to clear what you printed. Overwriting via \r doesn't always work especially if the new line is shorter than the old one. You will get traces from the old line, so I need clearing first.
Thanks.
\x1b[2K is what's known as an ANSI terminal control sequence. They are a legacy of the 1970s and still used today (but vastly extended) to control terminal emulators.
\x1b is the ASCII for ESCAPE (literally the ESC key on your keyboard). [2K is the command "erase the current line".
There are many libraries in Python for working with the terminal, such as Urwid. These libraries will hide the inner workings of the terminal from you and give you higher-level constructs to create TUIs.
However, there is a much more efficient way of doing this:
You can use the print() command as usual, and delete the screen using
os.system("cls") # For Windows
or
os.system("clear") # For Linux
Alternative to print on a single line
I have a script that prints the x, y coordinates of the mouse as such:
import pyautogui
import time
while True:
x, y = pyautogui.position()
position_string = "X: {} Y: {}".format(str(x).rjust(4), str(y).rjust(4))
print(position_string, end='')
print('\b' * len(position_string), end='', flush=True)
time.sleep(1)
Where I will point out that you can print the backspace character ('\b') the amount of times that there are characters on the screen (len(position_string)), and when used with the end='' and flush=True options this will constantly print on a single line within your console. I should also note that this does not work in IDLE, but only on an actual command line! In IDLE the backspace characters are actually printed as some weird square shape...
This is called ANSI escape code . 2K is the name for Erase in Line. Quote from the link:
Erases part of the line. If n is 0 (or missing), clear from cursor to the end of the line. If n is 1, clear from cursor to beginning of the line. If n is 2, clear entire line. Cursor position does not change.
You can also try echo -e '\x1b[2k' in the terminal for better understanding.
Related
I am using '\r' in print function in python 2.7. It works fine in terminal but not in terminator.
For example:
I am using a decrement counter which decrements from n to 0. In the Terminal, the count values are updated at the same line while in terminator, it count values get printed on new line. I am using terminator for various reasons such as its advanced features like tab partitioning etc. Below is the code snapshot
import sys
import time
if __name__ == "__main__":
sleep_time_in_sec = 15
time_to_go_back_mns = 10
for remaining in range(sleep_time_in_sec, -1, -1):
sys.stdout.write("\r")
sys.stdout.write(
"{:2d} seconds remaining to read last {:2d} minutes of data and perform prediction .....".format(remaining,
time_to_go_back_mns))
sys.stdout.flush()
time.sleep(1)
Can someone please suggest a fix
Simply place the \r at the end of your write statement like so:
sys.stdout.write(
"{:2d} seconds remaining to read last {:2d} minutes of data and perform prediction .....\r".format(remaining,
time_to_go_back_mns))
New data will then overwrite the line, you can use flush() to clear the line before writing to it again:
sys.stdout.flush()
Make sure that on the terminator side of things your profile settings are clean. Be sure to check out the compatibility tab as it mentions weird application behaviour.
note that carriage return stops functioning if the terminal size is too small. It will only return to the first character of the LAST line
Original answer
\r actually means "carriage return" whereas \n is a line feed.
In Linux (Unix) you'd usually use either a \n or \r\n.
So if your goal is to go to a new line you should use \n instead.
The reason it might work in the "terminal" (whichever one that might be) is because some terminals (notably gnome's terminal) catches the \r and treats it as a \r\n.
The answer for this post goes to #Rick van Lieshout.
In my case, I was using multiple tabs in the same window as a result of which \r was not working. It worked fine when I used it in a separate window or a tab with full horizontal width.
Is it possible to manipulate lines of text that have already been printed to the console?
For example,
import time
for k in range(1,100):
print(str(k)+"/"+"100")
time.sleep(0.03)
#>> Clear the most recent line printed to the console
print("ready or not here I come!")
I've seen some things for using custom DOS consoles under Windows, but I would really like something that works on the command_line like does print without any additional canvases.
Does this exist? If it doesn’t, why not?
P.S.: I was trying to use curses, and it was causing problems with my command line behaviour outside of Python. (After erroring out of a Python script with curses in it, my Bash shell stopped printing newline -unacceptable- ).
What you're looking for is:
print("{}/100".format(k), "\r", end="")
\r is carriage return, which returns the cursor to the beginning of the line. In effect, whatever is printed will overwrite the previous printed text. end="" is to prevent \n after printing (to stay on the same line).
A simpler form as suggested by sonrad10 in the comments:
print("{}/100".format(k), end="\r")
Here, we're simply replacing the end character with \r instead of \n.
In Python 2, the same can be achieved with:
print "{}/100".format(k), "\r",
What you need are ANSI Command Codes.
http://en.wikipedia.org/wiki/ANSI_escape_code#CSI_codes
You also need code to activate ANSI Command Codes. I would use Colorama.
https://pypi.python.org/pypi/colorama
OR
Use curses (Python 3.4+) module.
The simplest method (at least for Python 2.7) is to use the syntax:
print 'message', '\r',
print 'this new message now covers the previous'
Notice the extra ',' at the end of the first print. This makes print stay on the same line. Meanwhile, the '\r' puts the print at the beginning of that line. So the second print statement overwrites the first.
Can someone please thoroughly explain how a '\r' works in Python?
Why isn't the following code printing out anything on the screen?
#!/usr/bin/python
from time import sleep
for x in range(10000):
print "%d\r" % x,
sleep(1)
Your output is being buffered, so it doesn't show up immediately. By the time it does, it's being clobbered by the shell or interpreter prompt.
Solve this by flushing each time you print:
#!/usr/bin/python
from time import sleep
import sys
for x in range(10000):
print "%d\r" % x,
sys.stdout.flush()
sleep(1)
'\r' is just a another ASCII code character. By definition it is a CR or carriage return. It's the terminal or console being used that will determine how to interpret it. Windows and DOS systems usually expect every line to end in CR/LF ('\r\n') while Linux systems are usually just LF ('\n'), classic Mac was just CR ('\r'); but even on these individual systems you can usually tell your terminal emulator how to interpret CR and LF characters.
Historically (as a typewriter worked), LF bumped the cursor to the next line and CR brought it back to the first column.
To answer the question about why nothing is printing: remove the comma at the end of your print line.
Do this instead:
print "\r%d" % x,
This has nothing to do with \r. The problem is the trailing , in your print statement. It's trying to print the last value on the line, and the , is creating a tuple where the last value is empty. Lose the , and it'll work as intended.
Edit:
I'm not sure it's actually correct to say that it's creating a tuple, but either way that's the source of your problem.
I am trying to update the last line in PyCharm's console. Say, I print a and then I want to change it to c. However, I encounter the following problem. When I run:
print 'a\bc'
it prints
a c
while the desired output (which is also what I see in the Windows console) is:
c
Is there a way to move the cursor back in PyCharm's console? or maybe delete the whole line?
This is not a bug, this is a limitation of the interactive console found both in PyCharm, and in the IDLE shell.
When using the command prompt of windows, or a linux shell - the \b character is interpreted as a backspace and implemented as it is being parsed - However, in the interactive console of PyCharm and IDLE the \b character and many others are disabled, and instead you simply get the ASCII representation of the character (a white space in most cases).
It's a known bug: http://youtrack.jetbrains.com/issue/PY-11300
If you care about this, please get an account on the bug tracker and upload the bug to give it more attention.
The \r works. I know this is ASCII Carriage Return, but i use this as a workaround
print("\ra")
print("\rc")
will yield in c in the console
By the way, backspace is a ASCII Character
I just ran into the same issue in PyCharm (2019.1) and stumbled on this post. It turns out that you can use the \b character if you use the sys.stdout.write function instead of print. I wasn't able to get any of the above examples working within PyCharm using the print function.
Here's how I update the last line of text in my code assuming I don't need more than 100 characters:
# Initialize output line with spaces
sys.stdout.write(' ' * 100)
# Update line in a loop
for k in range(10)
# Generate new line of text
cur_line = 'foo %i' % k
# Remove last 100 characters, write new line and pad with spaces
sys.stdout.write('\b' * 100)
sys.stdout.write(cur_line + ' '*(100 - len(cur_line)))
# ... do other stuff in loop
This should generate "foo 1", then replaced with "foo 2", "foo 3", etc. all on the same line and overwriting the previous output for each string output. I'm using spaces to pad everything because different programs implement the backspace character differently, where sometimes it removes the character, and other times it only moves the cursor backwards and thus still requires new text to overwrite.
I've got to credit the Keras library for this solution, which correctly updates the console output (including PyCharm) during learning. I found that they were using the sys.stdout.write function in their progress bar update code.
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?
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.
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
If your terminal is line-buffered, you may need a sys.stdout.flush() to see your printing if you don't issue a linefeed.