Find previous character in console in python

Question

Is there a way to find the previous character(s) in the console in python?

print('Hello', end='')

should return 'o'.

If there is a way to do this, how can I get the previous x characters? e.g. 'lo' if I want 2 characters. Should also work for tracebacks.

There's no clean way to get back data you sent to the stdout stream. However, you can redirect stdout to string that you can inspect later: https://stackoverflow.com/questions/1218933/can-i-redirect-the-stdout-in-python-into-some-sort-of-string-buffer — Mike67, Aug 03 '20 at 02:56
Standard output is an _output_, not an input. Unless you're just trying to do some logging or record a run of something, that content is too late to work with at that point. If you wanted to work with `'Hello'`, you should save it to a variable with e.g. `my_string = 'Hello'`. If you want to work with the text of tracebacks, you can catch the exception and save it to a variable. — TigerhawkT3, Aug 03 '20 at 03:01

score 0 · Answer 1 · answered Aug 03 '20 at 03:05

Have you tried using subprocess and PIPE your output of the script you are running. Ex: You want to get console output from:

#script1.py
print('Hello',end='')

Creating a subprocess will let you run and get the STDOUT & STDERR

#subproc.py
from subprocess import Popen, PIPE
process = Popen(['python','script1.py'],stdout=PIPE,stderr=PIPE,shell=True)
stdout,stderr = process.communicate()
print(stdout.decode('utf-8')) #console output
print(stderr.decode('utf-8')) #traceback, empty if there's no error

#From there you can manipulate string
print(stdout.decode('utf-8')[-1:]) #will print string 'o'

score 0 · Answer 2 · answered Aug 03 '20 at 03:27

Perhaps you need something similar that what Expect does.

Check this code:

import pty
import os

my_list_accumulator = []

def read_stuff(fd):
    output = os.read(fd, 1024)
    my_list_accumulator.append(output)
    return output

pty.spawn('python3', read_stuff)

Demo:

>>> import pty
>>> import os
>>> 
>>> my_list_accumulator = []
>>> 
>>> def read_stuff(fd):
...     output = os.read(fd, 1024)
...     my_list_accumulator.append(output)
...     return output
...     
... 
>>> pty.spawn('python3', read_stuff)
Python 3.5.2 (default, Jul 17 2020, 14:04:10) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print('Hello', end='')
Hello>>> And this will give error
  File "<stdin>", line 1
    And this will give error
           ^
SyntaxError: invalid syntax
>>> 
0
>>> # pressed Ctrl-D to escape
... 
>>> print(b''.join(my_list_accumulator).decode('utf-8'))
Python 3.5.2 (default, Jul 17 2020, 14:04:10) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print('Hello', end='')
Hello>>> And this will give error
  File "<stdin>", line 1
    And this will give error
           ^
SyntaxError: invalid syntax
>>> 

>>>

So, you can modify the read_stuff function to do what you wish, but make sure to read the documentation: https://docs.python.org/3/library/pty.html

Find previous character in console in python

2 Answers2