text codecs ready

text_codecs/alphanumeric.py

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+import string
+import codecs
+from custom_codecs.register import register_codec
+from easybits import Bits
+
+allowed_characters = string.ascii_letters + string.digits
+
+def encode(text):
+    """A (very) lossy encoder which only saves ASCII letters, numbers, and spaces.
+    Everything else is discarded. All whitespace (e.g. tabs) is converted into spaces.
+    """
+    ascii_characters = []
+    last_character_was_space = False
+    for char in text:
+        if char in allowed_characters:
+            ascii_characters.append(char)
+            last_character_was_space = False
+        elif char in string.whitespace and not last_character_was_space:
+            ascii_characters.append(' ')
+            last_character_was_space = True
+    ascii_text = ''.join(ascii_characters)
+    return Bits(ascii_text).bytes
+
+def decode(data):
+    """A decoder which reads bytes and returns (string, length), 
+    where length is the length of bytes consumed
+    """
+    text = ""
+    for i, byte in enumerate(data):
+        try:
+            text += Bits(byte, length=8).ascii
+        except OverflowError:
+            print(i, byte)
+            print(text + '|')
+            print("Error")
+            breakpoint()
+    return text
+    
+register_codec(encode, decode, "alphanumeric")

text_codecs/ascii7.py

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+from custom_codecs.register import register_codec
+from easybits import Bits
+
+def encode(text):
+    """An encoder which only handles ASCII: non-ASCII characters
+    are replaced with '?'. Once all the characters are ASCII, this encoder
+    writes the first seven bits of each byte (the first bit of every 
+    ASCII character is 0, so we can easily reconstruct the full byte 
+    when we decode). Therefore, this encoder compresses ASCII text into
+    7/8 of the usual size.
+    """
+    result = Bits()
+    for char in text:
+        try:
+            b = Bits(char, encoding='ascii')
+        except UnicodeEncodeError:
+            b = Bits('?')
+        result = result.concat(b[1:])
+    return result.bytes
+
+def decode(data):
+    """The matching decoder. Reads seven bits at a time, putting a 0 on 
+    the front to create a full byte. Then converts this byte into its 
+    ASCII representation.
+    """
+    bits = Bits(bytes(data))
+    text = ""
+    for i in range(0, len(bits), 7):
+        byte = Bits('0').concat(bits[i:i+7])
+        text += Bits(byte).ascii
+    return text
+
+register_codec(encode, decode, "ascii7")

text_codecs/register.py

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+import codecs
+
+def register_codec(encode, decode, name):
+    """Registers a codec so that it can later be used to encode
+    or decode strings and bytes.
+    """
+    def encode_wrapper(text):
+        return encode(text), len(text)
+
+    def decode_wrapper(data):
+        return decode(data), len(data)
+
+    def search_for_codec(query):
+        if query == name:
+            return codecs.CodecInfo(encode_wrapper, decode_wrapper, name=name)
+
+    codecs.register(search_for_codec)