How can I tell if a file is binary (non-text) in Python?

I am searching through a large set of files in Python, and keep getting matches in binary files. This makes the output look incredibly messy.

I know I could use grep -I, but I am doing more with the data than what grep allows for.

In the past, I would have just searched for characters greater than 0x7f, but utf8 and the like, make that impossible on modern systems. Ideally, the solution would be fast.

You can also use the mimetypes module:

import mimetypes
...
mime = mimetypes.guess_type(file)

It’s fairly easy to compile a list of binary mime types. For example Apache distributes with a mime.types file that you could parse into a set of lists, binary and text and then check to see if the mime is in your text or binary list.

Yet another method based on file(1) behavior:

>>> textchars = bytearray({7,8,9,10,12,13,27} | set(range(0x20, 0x100)) - {0x7f})
>>> is_binary_string = lambda bytes: bool(bytes.translate(None, textchars))

Example:

>>> is_binary_string(open('/usr/bin/python', 'rb').read(1024))
True
>>> is_binary_string(open('/usr/bin/dh_python3', 'rb').read(1024))
False

If you’re using python3 with utf-8 it is straight forward, just open the file in text mode and stop processing if you get an UnicodeDecodeError. Python3 will use unicode when handling files in text mode (and bytearray in binary mode) – if your encoding can’t decode arbitrary files it’s quite likely that you will get UnicodeDecodeError.

Example:

try:
    with open(filename, "r") as f:
        for l in f:
             process_line(l)
except UnicodeDecodeError:
    pass # Fond non-text data

If it helps, many many binary types begin with a magic numbers. Here is a list of file signatures.

Try this:

def is_binary(filename):
    """Return true if the given filename is binary.
    @raise EnvironmentError: if the file does not exist or cannot be accessed.
    @attention: found @ http://bytes.com/topic/python/answers/21222-determine-file-type-binary-text on 6/08/2010
    @author: Trent Mick <TrentM@ActiveState.com>
    @author: Jorge Orpinel <jorge@orpinel.com>"""
    fin = open(filename, 'rb')
    try:
        CHUNKSIZE = 1024
        while 1:
            chunk = fin.read(CHUNKSIZE)
            if '\0' in chunk: # found null byte
                return True
            if len(chunk) < CHUNKSIZE:
                break # done
    # A-wooo! Mira, python no necesita el "except:". Achis... Que listo es.
    finally:
        fin.close()

    return False

Here’s a suggestion that uses the Unix file command:

import re
import subprocess

def istext(path):
    return (re.search(r':.* text',
                      subprocess.Popen(["file", '-L', path], 
                                       stdout=subprocess.PIPE).stdout.read())
            is not None)

Example usage:

>>> istext('/etc/motd') 
True
>>> istext('/vmlinuz') 
False
>>> open('/tmp/japanese').read()
'\xe3\x81\x93\xe3\x82\x8c\xe3\x81\xaf\xe3\x80\x81\xe3\x81\xbf\xe3\x81\x9a\xe3\x81\x8c\xe3\x82\x81\xe5\xba\xa7\xe3\x81\xae\xe6\x99\x82\xe4\xbb\xa3\xe3\x81\xae\xe5\xb9\x95\xe9\x96\x8b\xe3\x81\x91\xe3\x80\x82\n'
>>> istext('/tmp/japanese') # works on UTF-8
True

It has the downsides of not being portable to Windows (unless you have something like the file command there), and having to spawn an external process for each file, which might not be palatable.

Use binaryornot library (GitHub).

It is very simple and based on the code found in this stackoverflow question.

You can actually write this in 2 lines of code, however this package saves you from having to write and thoroughly test those 2 lines of code with all sorts of weird file types, cross-platform.

Usually you have to guess.

You can look at the extensions as one clue, if the files have them.

You can also recognise know binary formats, and ignore those.

Otherwise see what proportion of non-printable ASCII bytes you have and take a guess from that.

You can also try decoding from UTF-8 and see if that produces sensible output.

A shorter solution, with a UTF-16 warning:

def is_binary(filename):
    """ 
    Return true if the given filename appears to be binary.
    File is considered to be binary if it contains a NULL byte.
    FIXME: This approach incorrectly reports UTF-16 as binary.
    """
    with open(filename, 'rb') as f:
        for block in f:
            if b'\0' in block:
                return True
    return False

We can use python itself to check if a file is binary, because it fails if we try to open binary file in text mode

def is_binary(file_name):
    try:
        with open(file_name, 'tr') as check_file:  # try open file in text mode
            check_file.read()
            return False
    except:  # if fail then file is non-text (binary)
        return True

If you’re not on Windows, you can use Python Magic to determine the filetype. Then you can check if it is a text/ mime type.

Here’s a function that first checks if the file starts with a BOM and if not looks for a zero byte within the initial 8192 bytes:

import codecs


#: BOMs to indicate that a file is a text file even if it contains zero bytes.
_TEXT_BOMS = (
    codecs.BOM_UTF16_BE,
    codecs.BOM_UTF16_LE,
    codecs.BOM_UTF32_BE,
    codecs.BOM_UTF32_LE,
    codecs.BOM_UTF8,
)


def is_binary_file(source_path):
    with open(source_path, 'rb') as source_file:
        initial_bytes = source_file.read(8192)
    return not any(initial_bytes.startswith(bom) for bom in _TEXT_BOMS) \
           and b'\0' in initial_bytes

Technically the check for the UTF-8 BOM is unnecessary because it should not contain zero bytes for all practical purpose. But as it is a very common encoding it’s quicker to check for the BOM in the beginning instead of scanning all the 8192 bytes for 0.

Try using the currently maintained python-magic which is not the same module in @Kami Kisiel’s answer. This does support all platforms including Windows however you will need the libmagic binary files. This is explained in the README.

Unlike the mimetypes module, it doesn’t use the file’s extension and instead inspects the contents of the file.

>>> import magic
>>> magic.from_file("testdata/test.pdf", mime=True)
'application/pdf'
>>> magic.from_file("testdata/test.pdf")
'PDF document, version 1.2'
>>> magic.from_buffer(open("testdata/test.pdf").read(1024))
'PDF document, version 1.2'

I came here looking for exactly the same thing–a comprehensive solution provided by the standard library to detect binary or text. After reviewing the options people suggested, the nix file command looks to be the best choice (I’m only developing for linux boxen). Some others posted solutions using file but they are unnecessarily complicated in my opinion, so here’s what I came up with:

def test_file_isbinary(filename):
    cmd = shlex.split("file -b -e soft '{}'".format(filename))
    if subprocess.check_output(cmd)[:4] in {'ASCI', 'UTF-'}:
        return False
    return True

It should go without saying, but your code that calls this function should make sure you can read a file before testing it, otherwise this will be mistakenly detect the file as binary.

I guess that the best solution is to use the guess_type function. It holds a list with several mimetypes and you can also include your own types. Here come the script that I did to solve my problem:

from mimetypes import guess_type
from mimetypes import add_type

def __init__(self):
        self.__addMimeTypes()

def __addMimeTypes(self):
        add_type("text/plain",".properties")

def __listDir(self,path):
        try:
            return listdir(path)
        except IOError:
            print ("The directory {0} could not be accessed".format(path))

def getTextFiles(self, path):
        asciiFiles = []
        for files in self.__listDir(path):
            if guess_type(files)[0].split("/")[0] == "text":
                asciiFiles.append(files)
        try:
            return asciiFiles
        except NameError:
            print ("No text files in directory: {0}".format(path))
        finally:
            del asciiFiles

It is inside of a Class, as you can see based on the ustructure of the code. But you can pretty much change the things you want to implement it inside your application. It`s quite simple to use. The method getTextFiles returns a list object with all the text files that resides on the directory you pass in path variable.

on *NIX:

If you have access to the file shell-command, shlex can help make the subprocess module more usable:

from os.path import realpath
from subprocess import check_output
from shlex import split

filepath = realpath('rel/or/abs/path/to/file')
assert 'ascii' in check_output(split('file {}'.format(filepth).lower()))

Or, you could also stick that in a for-loop to get output for all files in the current dir using:

import os
for afile in [x for x in os.listdir('.') if os.path.isfile(x)]:
    assert 'ascii' in check_output(split('file {}'.format(afile).lower()))

or for all subdirs:

for curdir, filelist in zip(os.walk('.')[0], os.walk('.')[2]):
     for afile in filelist:
         assert 'ascii' in check_output(split('file {}'.format(afile).lower()))

Most of the programs consider the file to be binary (which is any file that is not “line-oriented”) if it contains a NULL character.

Here is perl’s version of pp_fttext() (pp_sys.c) implemented in Python:

import sys
PY3 = sys.version_info[0] == 3

# A function that takes an integer in the 8-bit range and returns
# a single-character byte object in py3 / a single-character string
# in py2.
#
int2byte = (lambda x: bytes((x,))) if PY3 else chr

_text_characters = (
        b''.join(int2byte(i) for i in range(32, 127)) +
        b'\n\r\t\f\b')

def istextfile(fileobj, blocksize=512):
    """ Uses heuristics to guess whether the given file is text or binary,
        by reading a single block of bytes from the file.
        If more than 30% of the chars in the block are non-text, or there
        are NUL ('\x00') bytes in the block, assume this is a binary file.
    """
    block = fileobj.read(blocksize)
    if b'\x00' in block:
        # Files with null bytes are binary
        return False
    elif not block:
        # An empty file is considered a valid text file
        return True

    # Use translate's 'deletechars' argument to efficiently remove all
    # occurrences of _text_characters from the block
    nontext = block.translate(None, _text_characters)
    return float(len(nontext)) / len(block) <= 0.30

Note also that this code was written to run on both Python 2 and Python 3 without changes.

Source: Perl’s “guess if file is text or binary” implemented in Python

are you in unix? if so, then try:

isBinary = os.system("file -b" + name + " | grep text > /dev/null")

The shell return values are inverted (0 is ok, so if it finds “text” then it will return a 0, and in Python that is a False expression).

Simpler way is to check if the file consist NULL character (\x00) by using in operator, for instance:

b'\x00' in open("foo.bar", 'rb').read()

See below the complete example:

#!/usr/bin/env python3
import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('file', nargs=1)
    args = parser.parse_args()
    with open(args.file[0], 'rb') as f:
        if b'\x00' in f.read():
            print('The file is binary!')
        else:
            print('The file is not binary!')

Sample usage:

$ ./is_binary.py /etc/hosts
The file is not binary!
$ ./is_binary.py `which which`
The file is binary!

from binaryornot.check import is_binary
is_binary('filename')

Documentation