Python class to implement a gap buffer for accepting user input with editing features.

gap_buffer.py

class GapBuffer:
    def __init__(self, size, prefill=None):
        self._buffer = bytearray(size)
        self._gap_start = 0                # first element of gap
        self._gap_end = len(self._buffer)  # first element after gap
        if prefill != None:
            prefill_end = len(prefill) if (len(prefill) <= size) else size
            self._buffer[0:prefill_end] = prefill[0:prefill_end]
            self._gap_start = len(prefill)

    def __len__(self):
        return len(self._buffer) - (self._gap_end - self._gap_start)

    def __repr__(self):
        contiguous_buffer = self._buffer[0:self._gap_start] + self._buffer[self._gap_end:len(self._buffer)]
        return contiguous_buffer

    def __str__(self):
        return self.__repr__().decode('utf-8')

    @property
    def is_full(self):
        return True if (self._gap_start >= len(self._buffer)) else False
    
    def insert(self, c):
        if self.is_full == True:
            return None
        self._buffer[self._gap_start] = ord(c)
        if (self._gap_start < self._gap_end):
            self._gap_start = self._gap_start + 1
        return self._gap_start

    def delete(self):
        if (self._gap_start > 0):
            self._gap_start -= 1
        return self._gap_start

    def back(self):
        """
        Move insertion point one character closer to buffer's end.
        """
        if self._gap_start > 0:
            self._gap_start -= 1
            self._gap_end -= 1
            self._buffer[self._gap_end] = self._buffer[self._gap_start]
        return self._gap_start

    def forward(self):
        """
        Move insertion point one character closer to buffer's beginning.
        """
        if self._gap_end < len(self._buffer):
            self._buffer[self._gap_start] = self._buffer[self._gap_end]
            self._gap_start += 1
            self._gap_end += 1
        return self._gap_start