Python: convert utf-8 string to byte string

Question

I have the following function to parse utf-8 string from byte sequence

Note. "length_size" is the number of bytes it takes to represent utf-8 string length

def parse_utf8(self, bytes, length_size):

    length = bytes2int(bytes[0:length_size])
    value = ''.join(['%c' % b for b in bytes[length_size:length_size+length]])
    return value


def bytes2int(raw_bytes, signed=False):
    """
    Convert a string of bytes to an integer (assumes little-endian byte order)
    """
    if len(raw_bytes) == 0:
        return None
    fmt = {1:'B', 2:'H', 4:'I', 8:'Q'}[len(raw_bytes)]
    if signed:
        fmt = fmt.lower()
    return struct.unpack('<'+fmt, raw_bytes)[0]

I would like to write a function in the reverse order - that is, a function that takes a utf-8 encoded string and returns its representation as a byte string.

So far I have the following:

def create_utf8(self, utf8_string):
    return utf8_string.encode('utf-8')

When trying to test this error, I encountered the following error:

  File "writer.py", line 229, in create_utf8
return utf8_string.encode('utf-8')
UnicodeDecodeError: 'ascii' codec can't decode byte 0x98 in position 0: ordinal not in range(128)

If possible, I would like to adopt a structure for code similar to the parse_utf8 example. What am I doing wrong?

Thank you for your help!

UPDATE: test driver, now correct

def random_utf8_seq(self, length):
    # from http://www.w3.org/2001/06/utf-8-test/postscript-utf-8.html
    test_charset = u" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ ¡¢£¤¥¦§¨©ª«¬­ ®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿĂ㥹ĆćČčĎďĐđĘęĚěĹ弾ŁłŃńŇňŐőŒœŔŕŘřŚśŞşŠšŢţŤťŮůŰűŸŹźŻżŽžƒˆˇ˘˙˛˜˝–—‘’‚""„†‡•…‰‹›€™"

    utf8_seq = u""

    for i in range(length):
        utf8_seq += random.choice(test_charset)

    return utf8_seq

I get the following error:

input_str = self.random_utf8_seq(200)
  File "writer.py", line 226, in random_utf8_seq
print unicode(utf8_seq, "utf-8")
  UnicodeDecodeError: 'utf8' codec can't decode byte 0xbb in position 0: invalid start byte

Answer 1

utf-8 = > bytestring - , , str.encode, - u unicode:

# coding: utf-8
import random

    def random_utf8_seq(length):
        # from http://www.w3.org/2001/06/utf-8-test/postscript-utf-8.html
        test_charset = u" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ ¡¢£¤¥¦§¨©ª«¬­ ®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿĂ㥹ĆćČčĎďĐđĘęĚěĹ弾ŁłŃńŇňŐőŒœŔŕŘřŚśŞşŠšŢţŤťŮůŰűŸŹźŻżŽžƒˆˇ˘˙˛˜˝–—‘’‚""„†‡•…‰‹›€™"

        utf8_seq = u''

        for i in range(length):
            utf8_seq += random.choice(test_charset)

        print utf8_seq.encode('utf-8')
        return utf8_seq.encode('utf-8')

    print( type(random_utf8_seq(200)) )

- -

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<type 'str'>