Re: Changing filenames from Greeklish => Greek (subprocess complain)

Date	2013-06-10 10:15 +0200
From	Andreas Perstinger <andipersti@gmail.com>
Subject	Re: Changing filenames from Greeklish => Greek (subprocess complain)
References	(4 earlier) <3fbb5d0e-51fb-4aed-b829-8388304a9885@googlegroups.com> <51b4249d$0$30001$c3e8da3$5496439d@news.astraweb.com> <5b0d3d7c-e3a4-436d-a55f-26bd40064fd5@googlegroups.com> <51b475b0$0$30001$c3e8da3$5496439d@news.astraweb.com> <a64ba08f-2616-4715-818c-073f3d1e2ffb@googlegroups.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.2959.1370852149.3114.python-list@python.org> (permalink)

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On 10.06.2013 09:10, nagia.retsina@gmail.com wrote:
> Τη Κυριακή, 9 Ιουνίου 2013 3:31:44 μ.μ. UTC+3, ο χρήστης Steven D'Aprano έγραψε:
>
>> py> c = 'α'
>> py> ord(c)
>> 945
>
> The number 945 is the characters 'α' ordinal value in the unicode charset correct?

Yes, the unicode character set is just a big list of characters. The 
946th character in that list (starting from 0) happens to be 'α'.

> The command in the python interactive session to show me how many bytes
> this character will take upon encoding to utf-8 is:
>
>>>> s = 'α'
>>>> s.encode('utf-8')
> b'\xce\xb1'
>
> I see that the encoding of this char takes 2 bytes. But why two exactly?

That's how the encoding is designed. Haven't you read the wikipedia 
article which was already mentioned several times?

> How do i calculate how many bits are needed to store this char into bytes?

You need to understand how UTF-8 works. Read the wikipedia article.

> Trying to to the same here but it gave me no bytes back.
>
>>>> s = 'a'
>>>> s.encode('utf-8')
> b'a'

The encode method returns a byte object. It's length will tell you how 
many bytes there are:

 >>> len(b'a')
1
 >>> len(b'\xce\xb1')
2

The python interpreter will represent all values below 256 as ASCII 
characters if they are printable:

 >>> ord(b'a')
97
 >>> hex(97)
'0x61'
 >>> b'\x61' == b'a'
True

The Python designers have decided to use b'a' instead of b'\x61'.

>>py> c.encode('utf-8')
>> b'\xce\xb1'
>
> 2 bytes here. why 2?

Same as your first question.

>> py> c.encode('utf-16be')
>> b'\x03\xb1'
>
> 2 byets here also. but why 3 different bytes? the ordinal value of
> char 'a' is the same in unicode. the encodign system just takes the
> ordinal value end encode, but sinc eit uses 2 bytes should these 2 bytes
> be the same?

'utf-16be' is a different encoding scheme, thus it uses other rules to 
determine how each character is translated into a byte sequence.

>> py> c.encode('iso-8859-7')
>> b'\xe1'
>
> And also does '\x' means that the value is being respresented in hex way?
> and when i bin(6) i see '0b1000001'
>
> I should expect to see 8 bits of 1s and 0's. what the 'b' is tryign to say?
>
'\x' is an escape sequence and means that the following two characters 
should be interpreted as a number in hexadecimal notation (see also the 
table of allowed escape sequences: 
http://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals 
).

'0b' tells you that the number is printed in binary notation.
Leading zeros are usually discarded when a number is printed:
 >>> bin(70)
'0b1000110'
 >>> 0b100110 == 0b00100110
True
 >>> 0b100110 == 0b0000000000100110
True

It's the same with decimal notation. You wouldn't say 00123 is different 
from 123, would you?

Bye, Andreas

Thread

Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-07 18:53 +1000
  Re: Changing filenames from Greeklish => Greek (subprocess complain) alex23 <wuwei23@gmail.com> - 2013-06-07 02:41 -0700
  Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-07 04:53 -0700
    Re: Changing filenames from Greeklish => Greek (subprocess complain) MRAB <python@mrabarnett.plus.com> - 2013-06-07 15:29 +0100
      Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-07 11:52 -0700
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Zero Piraeus <schesis@gmail.com> - 2013-06-07 15:31 -0400
        Re: Changing filenames from Greeklish => Greek (subprocess complain) MRAB <python@mrabarnett.plus.com> - 2013-06-07 21:45 +0100
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Zero Piraeus <schesis@gmail.com> - 2013-06-07 19:24 -0400
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-08 12:52 +1000
          Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-07 23:49 -0700
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Chris Angelico <rosuav@gmail.com> - 2013-06-08 16:58 +1000
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-08 07:26 +0000
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Chris Angelico <rosuav@gmail.com> - 2013-06-08 17:40 +1000
            Re: Changing filenames from Greeklish => Greek (subprocess complain) MRAB <python@mrabarnett.plus.com> - 2013-06-08 17:32 +0100
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-08 09:53 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-08 10:35 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) MRAB <python@mrabarnett.plus.com> - 2013-06-08 18:48 +0100
    Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-07 15:33 +0000
    Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-08 12:49 +1000
    Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-08 21:01 +0300
      Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-08 19:01 +0000
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-08 14:14 -0700
          Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-09 08:32 +1000
          Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 07:46 +0300
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 06:25 +0000
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-09 18:02 +1000
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:03 -0700
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-08 14:21 -0700
          Re: Changing filenames from Greeklish => Greek (subprocess complain) Chris Angelico <rosuav@gmail.com> - 2013-06-09 08:10 +1000
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 01:11 -0700
    Re: Changing filenames from Greeklish => Greek (subprocess complain) Chris Angelico <rosuav@gmail.com> - 2013-06-09 04:47 +1000
      Re: Changing filenames from Greeklish => Greek (subprocess complain) nagia.retsina@gmail.com - 2013-06-08 22:09 -0700
        Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 06:45 +0000
          Re: Changing filenames from Greeklish => Greek (subprocess complain) nagia.retsina@gmail.com - 2013-06-09 00:00 -0700
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 08:15 +0000
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:14 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 03:32 -0700
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-09 19:16 +1000
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 12:36 +0000
                Re: Changing filenames from Greeklish => Greek (subprocess complain) nagia.retsina@gmail.com - 2013-06-09 10:25 -0700
          Re: Changing filenames from Greeklish => Greek (subprocess complain) Lele Gaifax <lele@metapensiero.it> - 2013-06-09 10:55 +0200
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:08 -0700
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Lele Gaifax <lele@metapensiero.it> - 2013-06-09 11:20 +0200
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:38 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Andreas Perstinger <andipersti@gmail.com> - 2013-06-09 14:24 +0200
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 13:13 +0000
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Benjamin Kaplan <benjamin.kaplan@case.edu> - 2013-06-09 13:05 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:42 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 03:37 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Larry Hudson <orgnut@yahoo.com> - 2013-06-10 00:51 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-10 01:11 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Larry Hudson <orgnut@yahoo.com> - 2013-06-11 00:20 -0700
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 11:50 +0000
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 05:18 -0700
          Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:00 -0700
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Cameron Simpson <cs@zip.com.au> - 2013-06-09 19:12 +1000
              Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-09 02:20 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Benjamin Kaplan <benjamin.kaplan@case.edu> - 2013-06-09 13:01 -0700
            Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-09 12:31 +0000
              Re: Changing filenames from Greeklish => Greek (subprocess complain) nagia.retsina@gmail.com - 2013-06-10 00:10 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Andreas Perstinger <andipersti@gmail.com> - 2013-06-10 10:15 +0200
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-10 01:54 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-10 02:59 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Andreas Perstinger <andipersti@gmail.com> - 2013-06-10 12:42 +0200
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-10 11:59 +0000
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Νικόλαος Κούρας <nikos.gr33k@gmail.com> - 2013-06-10 07:27 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) jmfauth <wxjmfauth@gmail.com> - 2013-06-10 12:48 -0700
                Re: Changing filenames from Greeklish => Greek (subprocess complain) Ned Batchelder <ned@nedbatchelder.com> - 2013-06-10 13:28 -0700

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