How to clean the console in Python?

Question

I am an Operating System user Ubuntu and when I want to clean the terminal, I use the command clear.

>>> clear

However, in the Python, how could I do to clear the terminal, when I use it on the command line?

Is there any simple way to do this?

Answer 1

Simply press ctrl + L (works on the shell too - you don’t even need to write clear).

This in the terminal. In a program, you can simply print a number of blank lines larger than the terminal size: print("\n" * 130), or, if you’re on Linux or Mac, print the ANSI sequence that erases the screen: print("\x1b[2J"). See more details below.

CTRL+L clears the screen if you’re on the terminal of some Linux - and maybe one or the other of the interactive Windows environments - but not in Idle, and other Python prompts integrated into the IDE’s - and it’s certainly not appropriate if you want to delete the screen from within a program (You cannot ask the user to type "Ctrl+L" to erase the screen :-) )

The reason there is no simple function call,in the standard Python library is that standard inputs and outputs are not thought of, in a generic programming language, always as a "terminal" - they represent an input data stream, and two output (stdout and stderr). But the language itself "doesn’t know" that is running on the terminal when some program runs. For programs specifically made for the terminal that want a more sophisticated interaction (including with the mouse), the standard Python library includes the module curses (see below).

The solution calling the external command - be the cls in windows or clear on Linux/Mac OS, with os.system works -but has a basic problem: it is an external program - a whole external process in the operating system, find the file on disk, create the process, to make an API call to the terminal. In terms of resource uses is the same as calling a key chain to open and lock the door again every time you leave the house.

Well - these programs to "erase the screen" - both the Unix clear and the DOS "cls", as the "clear" and the CTRL + L itself, do not do much more than simply print several blank lines, so that the contents of the current screen scroll up.

To do this in Python, simply print a single string with a sufficient number of "linefeeds" (the character represented by ' n' - whose decimal code is "10").

A little more boring is knowing the exact number of linefeeds needed to erase the screen exactly and without too many linefeeds. If that’s not a concern, a number like 130 blank lines is more than enough to roll a full HD terminal with size 4 font - so simply:

print ("\n" * 130) 

Guaranteed to erase any terminal, regardless of the type of S.O. without having to execute another process outside the Python interpreter just for that.

Of course, it is more elegant to print a number of blank lines only equal to the number of terminal lines - and no more than that. Among other things, a user accustomed to using the terminal can expect to be able to scroll the screen up to see the previous screen in the lines immediately preceding the first line of the blank screen (although the command clear Restore this historical too).

For this, from Python 3.3, there is the function get_terminal_size in the Python OS module. For those who are writing a program that will work in several versions of Python, the functionality can be encapsulated in a function like:

def clear():
    try:
        import os
        lines = os.get_terminal_size().lines
    except AttributeError:
        lines = 130
    print("\n" * lines)

But in Python 3.3 or above, just do:

import os
print("\n" * os.get_terminal_size().lines)

In addition, in Unixes, and perhaps in some Windows terminal/prompt programs, the "sequences ANSI" - that is, the terminal itself recognizes special sequences of characters that represent commands such as cleaning the screen, changing the font color, positioning the cursor -etc - are a very interesting "toy" - and much simpler than the module curses Python (of which I speak below). To erase the screen on any Linux terminal or most Unixes (I don’t know if Mac OS X works directly) - just print the sequence " x1b[2J" - (the " x1b" is the character <ESC> the same code that is generated by the key with that name). The sequence <ESC>[ starts several ANSI sequences. To see the exact sequences supported by your terminal, run the command infocmp in the shell.

By this technique, deleting the screen, and positioning the cursor in the first row and first column can be done like this:

print("\x1b[2J\x1b[1;1H")

(The print command prints by default an " n" - if in Python 3 use print("\x1b[2J\x1b[1;1H", end="") to avoid stopping at the second line - in Python2, it is worth putting a from __future__ import print_function at the beginning of the file and do the same.)

Remembering that - and from what I understood from the context of this question - if the idea is just to delete the screen while in interactive Python mode - in this case, the "Ctrl + L" will serve well.

For those who want to make a complex program with interaction by the terminal, my tip is always the following: if you are at this point, it is time to think about escaping from the terminal. Python allows interaction with various graphic libraries to create an application in a window of its own - which is much more comfortable for the end user. Users accustomed to command line interface will be happy to call the program from the system command line, passing options directly in the same - for this see the module argparse of the standard library.

If still the author prefers to create an interactive interface in the terminal, the tip is to use the module curses - also from the standard library - with it you get an object of type "window" (text) in the terminal, where you can position the cursor in exact places, erase the screen, change colors, etc... And with some work (not little) you can make an app with a really professional face - since the users of this program have been frozen in time since the 1990s. If that’s not the point, delete the screen with the print("\n" * 130) is enough.

With curses, you can erase the screen by doing:

import curses
window = curses.initscr()
window.clear()
window.refresh()

However the terminal will be in this "application" mode where "print" and "input" may have different results than in a normal terminal. In particular, it is important to position the cursor in the desired position of the screen before each print calling the function window.move(line, col) . Upon terminating the program, it is vital to return the terminal to the normal state by calling the function curses.endwin().

Answer 2

Try this:

import os
os.system('cls' if os.name == 'nt' else 'clear')

Follow the Soen link, here, has other alternatives as well.

Answer 3

Do:

>>> import os
>>> clear = lambda: os.system('clear')
>>> clear()

That way you just call the clear() when you want to clean, if you have Windows just swap clear for cls.

Answer 4

As you are Ubuntu Operating System user and want a simple way to do it. You can do so:

import os
os.system('clear') 

Answer 5

import os
if os.name == "nt":
    os.system("clear")
else:
    os.system("cls")