UTF-8 and stdin/stdout?

D

dave_140390

Hi,

I have problems getting my Python code to work with UTF-8 encoding
when reading from stdin / writing to stdout.

Say I have a file, utf8_input, that contains a single character, é,
coded as UTF-8:

$ hexdump -C utf8_input
00000000 c3 a9
00000002

If I read this file by opening it in this Python script:

$ cat utf8_from_file.py
import codecs
file = codecs.open('utf8_input', encoding='utf-8')
data = file.read()
print "length of data =", len(data)

everything goes well:

$ python utf8_from_file.py
length of data = 1

The contents of utf8_input is one character coded as two bytes, so
UTF-8 decoding is working here.

Now, I would like to do the same with standard input. Of course, this:

$ cat utf8_from_stdin.py
import sys
data = sys.stdin.read()
print "length of data =", len(data)

does not work:

$ [/c/DiskCopy] python utf8_from_stdin.py < utf8_input
length of data = 2

Here, the contents of utf8_input is not interpreted as UTF-8, so
Python believes there are two separate characters.

The question, then:
How could one get utf8_from_stdin.py to work properly with UTF-8?
(And same question for stdout.)

I googled around, and found rather complex stuff (see, for example,
http://blog.ianbicking.org/illusive-setdefaultencoding.html), but even
that didn't work: I still get "length of data = 2" even after
successively calling sys.setdefaultencoding('utf-8').

-- dave
 
A

Arnaud Delobelle

Hi,

I have problems getting my Python code to work with UTF-8 encoding
when reading from stdin / writing to stdout.

Say I have a file, utf8_input, that contains a single character, é,
coded as UTF-8:

$ hexdump -C utf8_input
00000000 c3 a9
00000002

If I read this file by opening it in this Python script:

$ cat utf8_from_file.py
import codecs
file = codecs.open('utf8_input', encoding='utf-8')
data = file.read()
print "length of data =", len(data)

everything goes well:

$ python utf8_from_file.py
length of data = 1

The contents of utf8_input is one character coded as two bytes, so
UTF-8 decoding is working here.

Now, I would like to do the same with standard input. Of course, this:

$ cat utf8_from_stdin.py
import sys
data = sys.stdin.read()
print "length of data =", len(data)

Shouldn't you do data = data.decode('utf8') ?
does not work:

$ [/c/DiskCopy] python utf8_from_stdin.py < utf8_input
length of data = 2
 
C

Chris

Hi,

I have problems getting my Python code to work with UTF-8 encoding
when reading from stdin / writing to stdout.

Say I have a file, utf8_input, that contains a single character, é,
coded as UTF-8:

        $ hexdump -C utf8_input
        00000000  c3 a9
        00000002

If I read this file by opening it in this Python script:

        $ cat utf8_from_file.py
        import codecs
        file = codecs.open('utf8_input', encoding='utf-8')
        data = file.read()
        print "length of data =", len(data)

everything goes well:

        $ python utf8_from_file.py
        length of data = 1

The contents of utf8_input is one character coded as two bytes, so
UTF-8 decoding is working here.

Now, I would like to do the same with standard input. Of course, this:

        $ cat utf8_from_stdin.py
        import sys
        data = sys.stdin.read()
        print "length of data =", len(data)

does not work:

        $ [/c/DiskCopy] python utf8_from_stdin.py < utf8_input
        length of data = 2

Here, the contents of utf8_input is not interpreted as UTF-8, so
Python believes there are two separate characters.

The question, then:
How could one get utf8_from_stdin.py to work properly with UTF-8?
(And same question for stdout.)

I googled around, and found rather complex stuff (see, for example,http://blog.ianbicking.org/illusive-setdefaultencoding.html), but even
that didn't work: I still get "length of data = 2" even after
successively calling sys.setdefaultencoding('utf-8').

-- dave

weird thing is 'c3 a9' is é on my side... and copy/pasting the é
gives me 'e9' with the first script giving a result of zero and second
script gives me 1
 
U

Ulrich Eckhardt

Chris said:
Say I have a file, utf8_input, that contains a single character, é,
coded as UTF-8:

$ hexdump -C utf8_input
00000000  c3 a9
00000002
[...]
weird thing is 'c3 a9' is é on my side... and copy/pasting the é
gives me 'e9' with the first script giving a result of zero and second
script gives me 1

Don't worry, it can be that those are equivalent. The point is that some
characters exist more than once and some exist in a composite form (e with
accent) and separately (e and combining accent).

Looking at http://unicode.org/charts I see that the letter above should have
codepoint 0xe9 (combined character) or 0x61 (e) and 0x301 (accent).

0xe9 = 1110 1001 (codepoint)
0xc3 0xa9 = 1100 0011 1010 1001 (UTF-8)

Anyhow, further looking at this shows that your editor simply doesn't
interpret the two bytes as UTF-8 but as Latin-1 or similar encoding, where
they represent the capital A with tilde and the copyrigth sign.

Uli
 
M

Martin v. Löwis

$ cat utf8_from_stdin.py
import sys
data = sys.stdin.read()
print "length of data =", len(data)

sys.stdin is a byte stream in Python 2, not a character stream.
To make it a character stream, do

sys.stdin = codecs.getreader("utf-8")(sys.stdin)

HTH,
Martin
 

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