Overwrite last printed line

[DeGerlash]

Hi everyone,

I'm quite new to Python programming, which is why this thread is located in the Homework section: it's not because of a teacher that I'm restricted in my use of syntax, it's because of my basic knowledge.

I'm trying to program a clock to learn how to make a piece of code overwrite the last line I printed out to the display, to simulate a clock. I've been doing some research (the internet is stuffed with threads about this, I'm sorry), but everyone justs keeps going on about this infamous '\r' - thing, which is the return carriage, I suppose, and which should erase the last line and print the next line in place of the last line. On my computer, that is not what it does though: it just prints the next line right besides the previous line, resulting in some sort of junk-line of concatenated print-lines. So I found out about this 'flush'-thing that should clear your last line, but instead of clearing, it just does the exact same as if it weren't there (even if I set is to 'False'). Is this related to the type of computer I have? I found it was device-specific, but I found that quite strange.

Here's the failing code:

import time
x=0
for x in range(0,20):
    print(time.ctime(), end="\r", flush=True)
    time.sleep(1)

And here's what it results:
>>> %Run joke.py
Sun Jan 7 11:40:47 2018Sun Jan 7 11:40:48 2018Sun Jan 7 11:40:49 2018Sun Jan 7 11:40:50 2018Sun Jan 7 11:40:51 2018Sun Jan 7 11:40:52 2018Sun Jan 7 11:40:53 2018Sun Jan 7 11:40:54 2018Sun Jan 7 11:40:55 2018Sun Jan 7 11:40:56 2018Sun Jan 7 11:40:57 2018Sun Jan 7 11:40:58 2018Sun Jan 7 11:40:59 2018Sun Jan 7 11:41:00 2018Sun Jan 7 11:41:01 2018Sun Jan 7 11:41:02 2018Sun Jan 7 11:41:03 2018Sun Jan 7 11:41:04 2018Sun Jan 7 11:41:05 2018Sun Jan 7 11:41:06 2018

[Gribouillis]

You said in another thread that you are running python code in the Thonny IDE. As far as I know, the '\r' method works only in a terminal or console (such as a cmd tool in windows). It will most likely not work in an IDE's python shell. In fact, it may be impossible to overwrite the last line in the Thonny IDE.

[wavic]

You do not need the flush parameter.

It works for me.

In [1]: for i in range(10): # stupid mistake :D
   ...:     print("i", end='\r')
   ...:     
i
In [2]: for i in range(10):
   ...:     print(i, end='\r')
   ...:     
9
In [3]: from time import sleep

In [4]: for i in range(10):
   ...:     print(i, end='\r')
   ...:     sleep(0.5)
   ...:     
9
In [5]: from time import ctime

In [6]: for i in range(10):
   ...:     print(ctime(), end='\r')
   ...:     sleep(0.5)
   ...:     
Sun Jan  7 13:30:15 2018
In [7]: 

[DeGerlash]

I'm so sorry but i can't seem to fix the last code :D what do I need to put where?

[Gribouillis]

@wavic It works for you, but you are not in the Thonny IDE, are you?

[snippsat]

In Thonny IDE it will not overwrite,i tried it.
@DeGerlash run script in command line(cmd),then it will work.

It do work in stand alone REPL from command line like ptpython(what i use) or IPYthon.

[wavic]

Yes, I do not have Thonny installed.
What I am saying is that the issue is not in the code.

[DeGerlash]

But in cmd, my program shuts down the minute it's done. How do I stop this? Without using time.sleep(10), as I am unable to do anything then.

[wavic]

You want to keep counting?

Just replace the for loop with a while loop:

while True:
    print(time.ctime(), end="\r")
    time.sleep(1)

This will print the time until you press ctrl+c

[snippsat]

But in cmd, my program shuts down the minute it's done.

If you start cmd first it will stay.
I mean you cd into folder with script and do python my_script.py.

DoubleClick to run,and want window to stay.

import time

for x in range(0,20):
    print(time.ctime(), end="\r", flush=True)
    time.sleep(1)

input('\n----- Press Enter to quit -----')