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29

I'm using this code to get standard output from an external program:

>>> from subprocess import *
>>> command_stdout = Popen(['ls', '-l'], stdout=PIPE).communicate()[0]

The communicate() method returns an array of bytes:

>>> command_stdout
b'total 0\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2\n'

However, I'd like to work with the output as a normal Python string. So that I could print it like this:

>>> print(command_stdout)
-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1
-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2

I thought that's what the binascii.b2a_qp() method is for, but when I tried it, I got the same byte array again:

>>> binascii.b2a_qp(command_stdout)
b'total 0\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2\n'

Anybody knows how to convert the byte array back to string? I mean, using the "batteries" instead of doing it manually.
And I'd like it to be ok with Python 3.

Thanks!

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4 Answers

up vote 140 down vote accepted

You need to decode the bytes object to produce a string:

>>> b"abcde"
b'abcde'
>>> b"abcde".decode("utf-8")
'abcde'
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12  
Love you. Thanks! – Tomas Sedovic Mar 3 '09 at 12:30
5  
This 'solution' was particularly hard to find (for me at least) considering it is such a simple problem ... I'd love to put a line somewhere the subprocess docs about this since I bet a good portion of newbies like me will hit this snag when using subprocess. Anybody know about contributing to the python docs? – mathtick Nov 4 '10 at 17:34
Yes, but given that this is the output from a windows command, shouldn't it instead be using ".decode('windows-1252')" ? – mcherm Jul 18 '11 at 19:48
6  
Using "windows-1252" is not reliable either (e.g., for other language versions of Windows), wouldn't it be best to use sys.stdout.encoding? – nikow Jan 3 '12 at 15:20
This is the second time I forgot about this and it’s still nowhere to be found in the documentation, not even in the unicode section. What a shame. – Profpatsch Apr 5 at 10:41
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up vote 17 down vote

You need to decode the byte string and turn it in to a character (unicode) string. 

b'hello'.decode(encoding)

or 

str(b'hello', encoding)
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up vote 9 down vote

I think what you actually want is this:

>>> from subprocess import *
>>> command_stdout = Popen(['ls', '-l'], stdout=PIPE).communicate()[0]
>>> command_text = command_stdout.decode(encoding='windows-1252')

Aaron's answer was correct, except that you need to know WHICH encoding to use. And I believe that Windows uses 'windows-1252'. It will only matter if you have some unusual (non-ascii) characters in your content, but then it will make a difference.

By the way, the fact that it DOES matter is the reason that Python moved to using two different types for binary and text data: it can't convert magically between them because it doesn't know the encoding unless you tell it! The only way YOU would know is to read the Windows documentation (or read it here).

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up vote 3 down vote

I think easy on this way:

bytes = [112, 52, 52]
"".join(map(chr, bytes))
>> p44
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