Source code for escpos.magicencode

#  -*- coding: utf-8 -*-
""" Magic Encode

This module tries to convert an UTF-8 string to an encoded string for the printer.
It uses trial and error in order to guess the right codepage.
The code is based on the encoding-code in py-xml-escpos by @fvdsn.

:author: `Patrick Kanzler <>`_
:organization: `python-escpos <>`_
:copyright: Copyright (c) 2016 Patrick Kanzler and Frédéric van der Essen
:license: MIT

from builtins import bytes
from .constants import CODEPAGE_CHANGE
from .exceptions import Error
from .codepages import CodePages
import six

[docs]class Encoder(object): """Takes a list of available code spaces. Picks the right one for a given character. Note: To determine the code page, it needs to do the conversion, and thus already knows what the final byte in the target encoding would be. Nevertheless, the API of this class doesn't return the byte. The caller use to do the character conversion itself. $ python -m timeit -s "{u'ö':'a'}.get(u'ö')" 100000000 loops, best of 3: 0.0133 usec per loop $ python -m timeit -s "u'ö'.encode('latin1')" 100000000 loops, best of 3: 0.0141 usec per loop """ def __init__(self, codepage_map): self.codepages = codepage_map self.available_encodings = set(codepage_map.keys()) self.available_characters = {} self.used_encodings = set()
[docs] def get_sequence(self, encoding): return int(self.codepages[encoding])
[docs] def get_encoding_name(self, encoding): """Given an encoding provided by the user, will return a canonical encoding name; and also validate that the encoding is supported. TODO: Support encoding aliases: pc437 instead of cp437. """ encoding = CodePages.get_encoding_name(encoding) if encoding not in self.codepages: raise ValueError( ( 'Encoding "{}" cannot be used for the current profile. ' "Valid encodings are: {}" ).format(encoding, ",".join(self.codepages.keys())) ) return encoding
@staticmethod def _get_codepage_char_list(encoding): """Get codepage character list Gets characters 128-255 for a given code page, as an array. :param encoding: The name of the encoding. This must appear in the CodePage list """ codepage = CodePages.get_encoding(encoding) if "data" in codepage: encodable_chars = list("".join(codepage["data"])) assert len(encodable_chars) == 128 return encodable_chars elif "python_encode" in codepage: encodable_chars = [u" "] * 128 for i in range(0, 128): codepoint = i + 128 try: encodable_chars[i] = bytes([codepoint]).decode( codepage["python_encode"] ) except UnicodeDecodeError: # Non-encodable character, just skip it pass return encodable_chars raise LookupError("Can't find a known encoding for {}".format(encoding)) def _get_codepage_char_map(self, encoding): """Get codepage character map Process an encoding and return a map of UTF-characters to code points in this encoding. This is generated once only, and returned from a cache. :param encoding: The name of the encoding. """ # Skip things that were loaded previously if encoding in self.available_characters: return self.available_characters[encoding] codepage_char_list = self._get_codepage_char_list(encoding) codepage_char_map = dict( (utf8, i + 128) for (i, utf8) in enumerate(codepage_char_list) ) self.available_characters[encoding] = codepage_char_map return codepage_char_map
[docs] def can_encode(self, encoding, char): """Determine if a character is encodeable in the given code page. :param encoding: The name of the encoding. :param char: The character to attempt to encode. """ available_map = {} try: available_map = self._get_codepage_char_map(encoding) except LookupError: return False # Decide whether this character is encodeable in this code page is_ascii = ord(char) < 128 is_encodable = char in available_map return is_ascii or is_encodable
@staticmethod def _encode_char(char, charmap, defaultchar): """Encode a single character with the given encoding map :param char: char to encode :param charmap: dictionary for mapping characters in this code page """ if ord(char) < 128: return ord(char) if char in charmap: return charmap[char] return ord(defaultchar)
[docs] def encode(self, text, encoding, defaultchar="?"): """Encode text under the given encoding :param text: Text to encode :param encoding: Encoding name to use (must be defined in capabilities) :param defaultchar: Fallback for non-encodable characters """ codepage_char_map = self._get_codepage_char_map(encoding) output_bytes = bytes( [self._encode_char(char, codepage_char_map, defaultchar) for char in text] ) return output_bytes
def __encoding_sort_func(self, item): key, index = item return (key in self.used_encodings, index)
[docs] def find_suitable_encoding(self, char): """The order of our search is a specific one: 1. code pages that we already tried before; there is a good chance they might work again, reducing the search space, and by re-using already used encodings we might also reduce the number of codepage change instructiosn we have to send. Still, any performance gains will presumably be fairly minor. 2. code pages in lower ESCPOS slots first. Presumably, they are more likely to be supported, so if a printer profile is missing or incomplete, we might increase our change that the code page we pick for this character is actually supported. """ sorted_encodings = sorted(self.codepages.items(), key=self.__encoding_sort_func) for encoding, _ in sorted_encodings: if self.can_encode(encoding, char): # This encoding worked; at it to the set of used ones. self.used_encodings.add(encoding) return encoding
[docs]def split_writable_text(encoder, text, encoding): """Splits off as many characters from the begnning of text as are writable with "encoding". Returns a 2-tuple (writable, rest). """ if not encoding: return None, text for idx, char in enumerate(text): if encoder.can_encode(encoding, char): continue return text[:idx], text[idx:] return text, None
[docs]class MagicEncode(object): """A helper that helps us to automatically switch to the right code page to encode any given Unicode character. This will consider the printers supported codepages, according to the printer profile, and if a character cannot be encoded with the current profile, it will attempt to find a suitable one. If the printer does not support a suitable code page, it can insert an error character. """ def __init__( self, driver, encoding=None, disabled=False, defaultsymbol="?", encoder=None ): """ :param driver: :param encoding: If you know the current encoding of the printer when initializing this class, set it here. If the current encoding is unknown, the first character emitted will be a codepage switch. :param disabled: :param defaultsymbol: :param encoder: """ if disabled and not encoding: raise Error("If you disable magic encode, you need to define an encoding!") self.driver = driver self.encoder = encoder or Encoder(driver.profile.get_code_pages()) self.encoding = self.encoder.get_encoding_name(encoding) if encoding else None self.defaultsymbol = defaultsymbol self.disabled = disabled
[docs] def force_encoding(self, encoding): """Sets a fixed encoding. The change is emitted right away. From now one, this buffer will switch the code page anymore. However, it will still keep track of the current code page. """ if not encoding: self.disabled = False else: self.write_with_encoding(encoding, None) self.disabled = True
[docs] def write(self, text): """Write the text, automatically switching encodings.""" if self.disabled: self.write_with_encoding(self.encoding, text) return # See how far we can go into the text with the current encoding to_write, text = split_writable_text(self.encoder, text, self.encoding) if to_write: self.write_with_encoding(self.encoding, to_write) while text: # See if any of the code pages that the printer profile # supports can encode this character. encoding = self.encoder.find_suitable_encoding(text[0]) if not encoding: self._handle_character_failed(text[0]) text = text[1:] continue # Write as much text as possible with the encoding found. to_write, text = split_writable_text(self.encoder, text, encoding) if to_write: self.write_with_encoding(encoding, to_write)
def _handle_character_failed(self, char): """Called when no codepage was found to render a character.""" # Writing the default symbol via write() allows us to avoid # unnecesary codepage switches. self.write(self.defaultsymbol)
[docs] def write_with_encoding(self, encoding, text): if text is not None and type(text) is not six.text_type: raise Error( "The supplied text has to be unicode, but is of type {type}.".format( type=type(text) ) ) # We always know the current code page; if the new codepage # is different, emit a change command. if encoding != self.encoding: self.encoding = encoding self.driver._raw( CODEPAGE_CHANGE + six.int2byte(self.encoder.get_sequence(encoding)) ) if text: self.driver._raw(self.encoder.encode(text, encoding))