python array element prefixed with 'u'

Question

I have a function using popen() that returns stdout as an array.

using Python3 the arrays are returned correctly, but under python 2.7 each element is prefixed with a 'u'

def exe(cmd):
    from subprocess import Popen, PIPE, STDOUT
    p = Popen(cmd, shell=True, stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
    arr = p.stdout.read().decode().split("\n")
    print(arr)
    del arr[-1]
    if(arr[0]=='not found.'): arr = [];
    return arr

[u'10-000801d5a12d', u'']

Where is this 'u' coming from and how do I prevent it ?

You don't prevent it. When you print the list you get the representation of the content, not the value. — Matthias
– Matthias, Commented Nov 3, 2013 at 12:12
Only partially tongue-in-cheek answer - prevent it by switching Python 3.x! As far as I am aware, the worst thing about pre-3.x Python was strings' unicode support. — rlms
– rlms, Commented Nov 3, 2013 at 12:27

Alastair McCormack · Accepted Answer · 2013-11-03 12:25:19Z

1

The u indicates the string is a Unicode string. This means that the string has been decoded from an encoding, such as UTF-8 or ISO-8895-1, into a unambiguous type. If you print arr[0] it will be encoded back to your terminal without the u.

This would have happened during the .read().decode(). You should really pass the proper file encoding to decode otherwise a system one could be used which may not be appropriate. If your file contains just ASCII chars then you won't see a problem.

The reason why it's different is because in Python 3, normal strings (decoded) are always Unicode strings whereas byte strings (from .read()) are a special type.

If you really don't want the u, remove the .decode() method but you really don't need to.

answered Nov 3, 2013 at 12:25

Alastair McCormack

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Suhail Patel · Accepted Answer · 2013-11-03 12:10:20Z

1

The u stands for unicode to indicate it is a unicode string when printed. It doesn't affect the array contents in any way and is merely an indication

answered Nov 3, 2013 at 12:10

Suhail Patel

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Kobi K · Accepted Answer · 2013-11-03 12:10:25Z

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u'10-000801d5a12d' means '10-000801d5a12d' is a unicode string.

You can see it here at python docs

Use:

str(myString)

You can also use encode if you need specific encoding:

"myString".encode('utf-8')

answered Nov 3, 2013 at 12:10

Kobi K

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Sandro Munda · Accepted Answer · 2013-11-03 12:10:56Z

0

The u means the string is a unicode string. If you really want a python str, you can cast it like that:

str(my_var)

answered Nov 3, 2013 at 12:10

Sandro Munda

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