A script which simulate a person who writes a text

textwriter.py

import re
import pygame
import itertools

from pygame.locals import *


NULLCHAR = '\0'
BACKSPACE = '\b'
LEFT = '\1'
RIGHT = '\2'


pygame.init()
pygame.font.init()


class TextWriter(pygame.surface.Surface):

    '''
    Class which simulate a person who writes a text

    Usage:
    >>> writer = TextWriter()
    >>> writer.push('PRESS ENTER\0\0\0\b\b\b\b\bKEY\1\1\1A \2\2\2')
    >>> writer.update()
    '''

    def __init__(self, font=None, size=30, color=(255, 255, 255)):

        self.textiter = iter('')
        self.textwritten = []
        self.font = pygame.font.Font(font, size)
        self.color = color
        self.cursortime = 3
        self.cursorfreq = 2
        self.cursorblink = 0
        self.cursorindex = 0
        self.update()

    def push(self, text):

        self.textiter = itertools.chain(self.textiter, text)

    def update(self):

        try:
            char = next(self.textiter)
        except StopIteration:
            pass
        else:
            if char == BACKSPACE:
                if self.textwritten:
                    self.cursorindex -= 1
                    self.textwritten.pop(self.cursorindex)
            elif char == LEFT:
                self.cursorindex -= 1
            elif char == RIGHT:
                self.cursorindex += 1
            elif char != NULLCHAR:
                self.textwritten.insert(self.cursorindex, char)
                self.cursorindex += 1

        self.cursorblink += 1
        self.cursorblink %= (self.cursortime + self.cursorfreq)
        text = self.font.render(''.join(self.textwritten), True, self.color)
        cursor = self.font.render((self.textwritten + ['_'])[self.cursorindex], True, self.color, self.color)
        cursor.set_alpha(255 if self.cursorblink < self.cursortime else 0)
        cursorrect = cursor.get_rect()
        cursorrect.bottomright = self.font.size(''.join(self.textwritten[:self.cursorindex]) + '_')

        super(TextWriter, self).__init__((max(text.get_width(), cursorrect.right), text.get_height()), SRCALPHA)

        self.fill((0, 0, 0, 0))
        self.blit(text, (0, 0))
        self.blit(cursor, cursorrect)