In Python, how to change text after it's printed?

Question

I have a Python program I am writing and I want it to be able to change text after it is printed. For example, let's say I want to print "hello" and erase one letter every second. How would I go about doing that?

Also, I heard about curses but I can't get that to work, and I do not want to simply create new lines until the old text is off the screen.

Answer 1

Here's one way to do it.

print 'hello',
sys.stdout.flush()
...
print '\rhell ',
sys.stdout.flush()
...
print '\rhel ',
sys.stdout.flush()

You can probably also get clever with ANSI escapes. Something like

sys.stdout.write('hello')
sys.stdout.flush()
for _ in range(5):
    time.sleep(1)
    sys.stdout.write('\033[D \033[D')
    sys.stdout.flush()

Answer 2

For multi-line output, you can also clear the screen each time and reprint the entire thing:

from time import sleep
import os

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

message = 'hello'
for i in range(len(message), 0, -1):
    cls()
    print message[:i]
    sleep(1)

Answer 3

You could use this:

call these modules:

import time
import sys

Then copy this method:

    # Custom Print Method
    def custom_print(string, how = "normal", dur = 0, inline = True):

Copy just this part for the method to do typing

# string = the string to print & how = way to print & dur = time to print whole word or letter & inline = print on single line or not
if how == "typing": # if how is equal to typing then run this block of code
    letter = 1
    while letter <= len(string):
        new_string = string[0:letter]
        if inline: sys.stdout.write("\r")
        sys.stdout.write("{0}".format(new_string))
        if inline == False: sys.stdout.write("\n")
        if inline: sys.stdout.flush()
        letter += 1 
        time.sleep(float(dur))

OR just this part of the method for a string to print in reverse

if how == "reverse": # if how is equal to reverse then run this block of code
    new_string = string
    while len(new_string) > 0:
        if inline == True: sys.stdout.write("\r")
        sys.stdout.write('{message: <{fill}}'.format(message=new_string, fill=str(len(string))))
        if inline == False: sys.stdout.write("\n")
        if inline == True: sys.stdout.flush()
        new_string = new_string[0:len(new_string) - 1]
        time.sleep(float(dur))

OR just this part of the method for a normal string to print normally

if how == "normal": # if how is equal to normal then run this block of code
    sys.stdout.write("\r")
    sys.stdout.write(string)
    time.sleep(float(dur))
    sys.stdout.write("\n")

OR you can put all of it in the method for all the options

All you have to do is call custom_print() instead ofprint`

# custom_print("string", "howtoprint", seconds in int, inline:true or false)
custom_print("hello", "reverse", 1) # for reverse printing hello
custom_print("hello", "typing", 1) # for typing hello slowly
custom_print("hello", "normal", 0) # for just printing hello
custom_print("hello") # for just printing hello

Answer 4

import sys
import time
steps = 10
print("Total steps: "+str(steps),end=' ')
time.sleep(1)
for i in range(steps):
    sys.stdout.flush()
    print("\rStep "+str(i+1)+"/"+str(steps),end=' ')
    time.sleep(1)
print("")#to change the current line

Answer 5

Here's something that seems to work well:

import time

text = '\rgood-bye'
for i in xrange(len(text), 0, -1):
    print text[0:i],
    time.sleep(1)
print ' '

Answer 6

You could use dynamical stdout with getch() characters and loop

Example: https://asciinema.org/a/238478

Code:

# Script make you able to edit printed text
# stdin and stdout at the same time
# https://asciinema.org/a/238478
# https://gist.github.com/SoleSensei/05a97bbe8b75cd2368a8e6d5e00d6047
import sys
from getch import getch

def flush_append(char):
    # just append char to the end
    sys.stdout.write(char)
    sys.stdout.flush()

def flush_write(line):
    # clear all and rewrite line
    sys.stdout.write(f"\r{' '*100}\r")
    sys.stdout.flush()
    sys.stdout.write(line)
    sys.stdout.flush()

def interactive_input(line):
    flush_write(line)
    c = getch()
    while ord(c) not in (13, 3): # 13 - Enter, 3 - Ctrl+C
        if ord(c) in (127, 8): # 127,8 - Backspace (Unix, Windows)
            line = line[:-1]
            flush_write(line)
        else:
            # decode to string if byte
            c = c.decode('ascii') if str(c)[0] == 'b' else c
            line += c
            flush_append(c)
        c = getch()
    print() # add EOL
    return line


s = interactive_input('stdout editable line')