Beginning a simple line-based text editor.

text-editor.py

try:
    import getch
except ImportError as e:
    print(f"Can't import getch: {e}.")

def get_character():
    """
    Wait for a character to be typed
    return tuple: 'in_char': character, 'asc': ascii value
    """
    in_char = None
    while in_char is None:
        # getch.getch() does not echo input
        in_char = getch.getch()
        asc = ord(in_char)
    return (in_char, asc)

def out_backspace(count):
    """
    Output <count> backspaces, character used depends on terminal
    """
    backspace = "\b \b"  # Linux terminal
    # if Character.terminal['translation'] == "PetSCII" then:
    #     backspace = chr(20)
    output = backspace * count
    return output

def yes_or_no(prompt="Are you sure", default=False):
    """
    Ask a yes-or-no question, with default answer.
    the response is yes (True), or no (False).
    prompt: configurable string
    default: unless any other key but 'y' for True or 'n' for False is typed
    returns: response: yes = True, no = False
    """
    if default is True:
        chars = "Y/n"
    if default is False:
        chars = "y/N"
    print(f"{prompt} [{chars}]: ", end="", flush=True)
    key, asc = get_character()
    command_char = key.lower()
    if default is True and command_char != "n":
        response = True
        print("Yes.\n")
    if default is False and command_char != "y":
        response = False
        print("No.\n")
    return response

def dot_cmd_list():
    """
    list text with line numbers
    """
    for k, v in enumerate(buffer, start=1):
        print(f"{k}:\n{v}")

print("Using getch:")
# init:
editing = True
buffer = ['', '']  # empty buffer, but 1-indexed
char_pos = 0
line = ''  # init empty line
line_num = 0
char_pos = 0

KEY_BACKSPACE = 127
KEY_RETURN = 10  # last char of CR/LF pair

prompt = "Command: "
debug = True
"""
editing: Boolean whether we're in the editor
char_pos: character position within line
line: the string input so far
line_num: the line number being edited (1-based)
char: character typed
asc: ascii value of char
"""
while editing is True:
    char, asc = get_character()
    # asc = ord(char)  # ascii value
    
    # handle column 0 dot/slash commands:
    if char_pos == 0:
        # print(char, asc)
        if char in ("/", "."):
            print(prompt, end="", flush=True)
            key, asc = get_character()
            command_char = key.lower()
            if command_char == "a":
                print("Abort")
                response = yes_or_no(default=False)
                if response is True:
                    editing = False
                continue
            if command_char == "l":
                print("List")
                dot_cmd_list()
                continue
            if command_char == "n":
                print("Erase Text")
                response = yes_or_no(default=False)
                if response is True:
                    buffer = ['', '']
                    print("Erased text.")
                continue
            if asc == KEY_BACKSPACE or asc == KEY_RETURN or command_char in ("/", "."):
                print(out_backspace(len(prompt)), end='', flush=True)
                continue
            else:
                print(f"{command_char} ({asc}) not implemented yet.")

    # handle backspace/delete:
    if asc == KEY_BACKSPACE and char_pos > 0:
        # print("BS/DEL", end='')
        char_pos -= 1
        line = line[:char_pos]
        print(out_backspace(1), end='', flush=True)

    elif asc == 10:
        # print(" [Return/Enter hit]\n")
        print()
        # if line_num > len(buffer):
        #     buffer.append(x for x in [line_num - len(buffer)]
        # TODO: fill in blank lines
        buffer[line_num] = line
        line_num += 1
        line = ''
        char_pos = 0

    else:
        # filter out control chars for now:
        if asc > 31 and asc < 197:
            # print(f"{asc if debug else ''}{char}", end='', flush=True)
            print(f"{char}", end='', flush=True)
            char_pos += 1
            line = line + char