Convert bytes to a string

Question:

I captured the standard output of an external program into a bytes object:

>>> from subprocess import *
>>> command_stdout = Popen(['ls', '-l'], stdout=PIPE).communicate()[0]
>>>
>>> command_stdout
b'total 0n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2n'

I want to convert that to a normal Python string, so that I can 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 tried the binascii.b2a_qp() method, but got the same bytes object again:

>>> binascii.b2a_qp(command_stdout)
b'total 0n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2n'

How do I convert the bytes object to a str with Python 3?

Asked By: Tomas Sedovic

||

Answers:

Decode the bytes object to produce a string:

>>> b"abcde".decode("utf-8") 
'abcde'

The above example assumes that the bytes object is in UTF-8, because it is a common encoding. However, you should use the encoding your data is actually in!

Answered By: Aaron Maenpaa

Decode the byte string and turn it in to a character (Unicode) string.


Python 3:

encoding = 'utf-8'
b'hello'.decode(encoding)

or

str(b'hello', encoding)

Python 2:

encoding = 'utf-8'
'hello'.decode(encoding)

or

unicode('hello', encoding)
Answered By: dF.

I think you actually want 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).

Answered By: mcherm

This joins together a list of bytes into a string:

>>> bytes_data = [112, 52, 52]
>>> "".join(map(chr, bytes_data))
'p44'
Answered By: Sisso

From sys — System-specific parameters and functions:

To write or read binary data from/to the standard streams, use the underlying binary buffer. For example, to write bytes to stdout, use sys.stdout.buffer.write(b'abc').

Answered By: Zhichang Yu

Set universal_newlines to True, i.e.

command_stdout = Popen(['ls', '-l'], stdout=PIPE, universal_newlines=True).communicate()[0]
Answered By: ContextSwitch

If you don’t know the encoding, then to read binary input into string in Python 3 and Python 2 compatible way, use the ancient MS-DOS CP437 encoding:

PY3K = sys.version_info >= (3, 0)

lines = []
for line in stream:
    if not PY3K:
        lines.append(line)
    else:
        lines.append(line.decode('cp437'))

Because encoding is unknown, expect non-English symbols to translate to characters of cp437 (English characters are not translated, because they match in most single byte encodings and UTF-8).

Decoding arbitrary binary input to UTF-8 is unsafe, because you may get this:

>>> b'x00x01xffsd'.decode('utf-8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 2: invalid
start byte

The same applies to latin-1, which was popular (the default?) for Python 2. See the missing points in Codepage Layout – it is where Python chokes with infamous ordinal not in range.

UPDATE 20150604: There are rumors that Python 3 has the surrogateescape error strategy for encoding stuff into binary data without data loss and crashes, but it needs conversion tests, [binary] -> [str] -> [binary], to validate both performance and reliability.

UPDATE 20170116: Thanks to comment by Nearoo – there is also a possibility to slash escape all unknown bytes with backslashreplace error handler. That works only for Python 3, so even with this workaround you will still get inconsistent output from different Python versions:

PY3K = sys.version_info >= (3, 0)

lines = []
for line in stream:
    if not PY3K:
        lines.append(line)
    else:
        lines.append(line.decode('utf-8', 'backslashreplace'))

See Python’s Unicode Support for details.

UPDATE 20170119: I decided to implement slash escaping decode that works for both Python 2 and Python 3. It should be slower than the cp437 solution, but it should produce identical results on every Python version.

# --- preparation

import codecs

def slashescape(err):
    """ codecs error handler. err is UnicodeDecode instance. return
    a tuple with a replacement for the unencodable part of the input
    and a position where encoding should continue"""
    #print err, dir(err), err.start, err.end, err.object[:err.start]
    thebyte = err.object[err.start:err.end]
    repl = u'\x'+hex(ord(thebyte))[2:]
    return (repl, err.end)

codecs.register_error('slashescape', slashescape)

# --- processing

stream = [b'x80abc']

lines = []
for line in stream:
    lines.append(line.decode('utf-8', 'slashescape'))
Answered By: anatoly techtonik

While @Aaron Maenpaa’s answer just works, a user recently asked:

Is there any more simply way? ‘fhand.read().decode(“ASCII”)’ […] It’s so long!

You can use:

command_stdout.decode()

decode() has a standard argument:

codecs.decode(obj, encoding='utf-8', errors='strict')

Answered By: serv-inc

I made a function to clean a list

def cleanLists(self, lista):
    lista = [x.strip() for x in lista]
    lista = [x.replace('n', '') for x in lista]
    lista = [x.replace('b', '') for x in lista]
    lista = [x.encode('utf8') for x in lista]
    lista = [x.decode('utf8') for x in lista]

    return lista
Answered By: eafloresf

In Python 3, the default encoding is "utf-8", so you can directly use:

b'hello'.decode()

which is equivalent to

b'hello'.decode(encoding="utf-8")

On the other hand, in Python 2, encoding defaults to the default string encoding. Thus, you should use:

b'hello'.decode(encoding)

where encoding is the encoding you want.

Note: support for keyword arguments was added in Python 2.7.

Answered By: lmiguelvargasf

To interpret a byte sequence as a text, you have to know the
corresponding character encoding:

unicode_text = bytestring.decode(character_encoding)

Example:

>>> b'xc2xb5'.decode('utf-8')
'µ'

ls command may produce output that can’t be interpreted as text. File names
on Unix may be any sequence of bytes except slash b'/' and zero
b'':

>>> open(bytes(range(0x100)).translate(None, b'/'), 'w').close()

Trying to decode such byte soup using utf-8 encoding raises UnicodeDecodeError.

It can be worse. The decoding may fail silently and produce mojibake
if you use a wrong incompatible encoding:

>>> '—'.encode('utf-8').decode('cp1252')
'—'

The data is corrupted but your program remains unaware that a failure
has occurred.

In general, what character encoding to use is not embedded in the byte sequence itself. You have to communicate this info out-of-band. Some outcomes are more likely than others and therefore chardet module exists that can guess the character encoding. A single Python script may use multiple character encodings in different places.


ls output can be converted to a Python string using os.fsdecode()
function that succeeds even for undecodable
filenames
(it uses
sys.getfilesystemencoding() and surrogateescape error handler on
Unix):

import os
import subprocess

output = os.fsdecode(subprocess.check_output('ls'))

To get the original bytes, you could use os.fsencode().

If you pass universal_newlines=True parameter then subprocess uses
locale.getpreferredencoding(False) to decode bytes e.g., it can be
cp1252 on Windows.

To decode the byte stream on-the-fly,
io.TextIOWrapper()
could be used: example.

Different commands may use different character encodings for their
output e.g., dir internal command (cmd) may use cp437. To decode its
output, you could pass the encoding explicitly (Python 3.6+):

output = subprocess.check_output('dir', shell=True, encoding='cp437')

The filenames may differ from os.listdir() (which uses Windows
Unicode API) e.g., 'xb6' can be substituted with 'x14'—Python’s
cp437 codec maps b'x14' to control character U+0014 instead of
U+00B6 (¶). To support filenames with arbitrary Unicode characters, see Decode PowerShell output possibly containing non-ASCII Unicode characters into a Python string

Answered By: jfs

For Python 3, this is a much safer and Pythonic approach to convert from byte to string:

def byte_to_str(bytes_or_str):
    if isinstance(bytes_or_str, bytes): # Check if it's in bytes
        print(bytes_or_str.decode('utf-8'))
    else:
        print("Object not of byte type")

byte_to_str(b'total 0n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2n')

Output:

total 0
-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1
-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2
Answered By: Taufiq Rahman

If you should get the following by trying decode():

AttributeError: ‘str’ object has no attribute ‘decode’

You can also specify the encoding type straight in a cast:

>>> my_byte_str
b'Hello World'

>>> str(my_byte_str, 'utf-8')
'Hello World'
Answered By: Broper

When working with data from Windows systems (with rn line endings), my answer is

String = Bytes.decode("utf-8").replace("rn", "n")

Why? Try this with a multiline Input.txt:

Bytes = open("Input.txt", "rb").read()
String = Bytes.decode("utf-8")
open("Output.txt", "w").write(String)

All your line endings will be doubled (to rrn), leading to extra empty lines. Python’s text-read functions usually normalize line endings so that strings use only n. If you receive binary data from a Windows system, Python does not have a chance to do that. Thus,

Bytes = open("Input.txt", "rb").read()
String = Bytes.decode("utf-8").replace("rn", "n")
open("Output.txt", "w").write(String)

will replicate your original file.

Answered By: bers

Since this question is actually asking about subprocess output, you have more direct approaches available. The most modern would be using subprocess.check_output and passing text=True (Python 3.7+) to automatically decode stdout using the system default coding:

text = subprocess.check_output(["ls", "-l"], text=True)

For Python 3.6, Popen accepts an encoding keyword:

>>> from subprocess import Popen, PIPE
>>> text = Popen(['ls', '-l'], stdout=PIPE, encoding='utf-8').communicate()[0]
>>> type(text)
str
>>> print(text)
total 0
-rw-r--r-- 1 wim badger 0 May 31 12:45 some_file.txt

The general answer to the question in the title, if you’re not dealing with subprocess output, is to decode bytes to text:

>>> b'abcde'.decode()
'abcde'

With no argument, sys.getdefaultencoding() will be used. If your data is not sys.getdefaultencoding(), then you must specify the encoding explicitly in the decode call:

>>> b'cafxe9'.decode('cp1250')
'café'
Answered By: wim
def toString(string):    
    try:
        return v.decode("utf-8")
    except ValueError:
        return string

b = b'97.080.500'
s = '97.080.500'
print(toString(b))
print(toString(s))
Answered By: Leonardo Filipe

If you want to convert any bytes, not just string converted to bytes:

with open("bytesfile", "rb") as infile:
    str = base64.b85encode(imageFile.read())

with open("bytesfile", "rb") as infile:
    str2 = json.dumps(list(infile.read()))

This is not very efficient, however. It will turn a 2 MB picture into 9 MB.

Answered By: HCLivess

For your specific case of “run a shell command and get its output as text instead of bytes”, on Python 3.7, you should use subprocess.run and pass in text=True (as well as capture_output=True to capture the output)

command_result = subprocess.run(["ls", "-l"], capture_output=True, text=True)
command_result.stdout  # is a `str` containing your program's stdout

text used to be called universal_newlines, and was changed (well, aliased) in Python 3.7. If you want to support Python versions before 3.7, pass in universal_newlines=True instead of text=True

Answered By: Boris Verkhovskiy

Try this:

bytes.fromhex('c3a9').decode('utf-8') 
Answered By: Victor Choy

Try using this one; this function will ignore all the non-character sets (like UTF-8) binaries and return a clean string. It is tested for Python 3.6 and above.

def bin2str(text, encoding = 'utf-8'):
    """Converts a binary to Unicode string by removing all non Unicode char
    text: binary string to work on
    encoding: output encoding *utf-8"""

    return text.decode(encoding, 'ignore')

Here, the function will take the binary and decode it (converts binary data to characters using the Python predefined character set and the ignore argument ignores all non-character set data from your binary and finally returns your desired string value.

If you are not sure about the encoding, use sys.getdefaultencoding() to get the default encoding of your device.

Answered By: Ratul Hasan

Decode with .decode(). This will decode the string. Pass in 'utf-8') as the value in the inside.

Answered By: Aarav Dave

If you have had this error:

utf-8 codec can’t decode byte 0x8a,

then it is better to use the following code to convert bytes to a string:

bytes = b"abcdefg"
string = bytes.decode("utf-8", "ignore") 
Answered By: Yasser M

We can decode the bytes object to produce a string using bytes.decode(encoding='utf-8', errors='strict').
For documentation see bytes.decode.

Python 3 example:

byte_value = b"abcde"
print("Initial value = {}".format(byte_value))
print("Initial value type = {}".format(type(byte_value)))
string_value = byte_value.decode("utf-8")
# utf-8 is used here because it is a very common encoding, but you need to use the encoding your data is actually in.
print("------------")
print("Converted value = {}".format(string_value))
print("Converted value type = {}".format(type(string_value)))

Output:

Initial value = b'abcde'
Initial value type = <class 'bytes'>
------------
Converted value = abcde
Converted value type = <class 'str'>

Note: In Python 3, by default the encoding type is UTF-8. So, <byte_string>.decode("utf-8") can be also written as <byte_string>.decode()

Answered By: Shubhank Gupta

Bytes

m=b'This is bytes'

Converting to string

Method 1

m.decode("utf-8")

or

m.decode()

Method 2

import codecs
codecs.decode(m,encoding="utf-8")

or

import codecs
codecs.decode(m)

Method 3

str(m,encoding="utf-8")

or

str(m)[2:-1]

Result

'This is bytes'
Answered By: Supergamer
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