Python将光标向前移动两个位置

Question

I have written the program below which is intended to act as the terminal UI for a chat I am about to build for a university project. At its present state, the aim is to always have the last line act as the area to write a message, and when enter is pressed the message is written above and the last line becomes blank again.

That works fine if that's all I want. But, I also want to always have a number of "prompt symbols" at the start of the last line, namely here :> . To make that happen, when enter is pressed,the whole current line is deleted, the bare message is printed, a newline character inserted, and finally I wish to print the :> in the new line and repeat.

What happens, however, is that the prompt string is indeed printed, but the cursor, after the first enter pressed, begins at the start of the line, which means any subsequent input will overwrite the prompt characters. That does not happen the first time for some reason, where the first prompt is printed before anything else happens.

So in the end, I would like for a way for the cursor to actually start after the two prompt characters when a newline is printed. This is all I want as regards to functionality of the terminal, therefore I would like to find an easy way to solve this and be done with it instead of meddling with ncurses library and the likes. Thank you all for your time. The point of interest in the code where happens whatever I want to happen is inside the last while loop.

The code should be run with Python3.

import sys
from string import printable
import termios
import tty

class _Getch:
    """Gets a single character from standard input.  Does not echo to the
    screen."""
    def __init__(self):
        try:
            self.impl = _GetchWindows()
        except ImportError:
            self.impl = _GetchUnix()

    def __call__(self): return self.impl()
class _GetchUnix:
    def __init__(self):
        import tty, sys

    def __call__(self):
        import sys, tty, termios
        fd = sys.stdin.fileno()
        old_settings = termios.tcgetattr(fd)
        try:
            tty.setraw(sys.stdin.fileno())
            # ch = sys.stdin.read(1)
            ch = sys.stdin.read(1)[0]
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
        return ch
class _GetchWindows:
    def __init__(self):
        import msvcrt

    def __call__(self):
        import msvcrt
        return msvcrt.getch()

# enter: ord 13
#backspace: ord 127

current_input = ""
prompt_msg = ":> "

print(10*"\n"+prompt_msg,end="")

getch = _Getch()

def clear_input():
    linelen = (len(current_input)+len(prompt_msg))
    sys.stdout.write("\b"*linelen+" "*linelen+"\b"*linelen)
    sys.stdout.flush()


while(True):

    ch=getch()
    if ord(ch)==3:# ctrl+c
        exit()
    # >>>>>>>.POINT OF INTEREST<<<<<<<<<<<
    if ord(ch)==13:# enter
        clear_input()
        print(current_input)
        current_input = ""

        # print(prompt_msg,end="")
        sys.stdout.write(prompt_msg)
        sys.stdout.flush()

    if ord(ch)==127 and len(current_input)>0:# backspace
        sys.stdout.write("\b"+" "+"\b")
        sys.stdout.flush()
        current_input=current_input[:-1]
    if ch in printable or ord(ch)>127: # printable
        current_input+=ch
        sys.stdout.write(ch)
        sys.stdout.flush()

Answer 1

与其尝试使指针向前移动两个位置，我没有运气寻找答案；我只是在应该完成的每个位置中，从current_input字符串中删除了回车符（“ \\ r”）-流氓回车字符在字符串中似乎还存在，这导致了问题。