python--magic module 文件类型识别

前言：接触magic module是由于工作中对的文件类型判断需求，网上查了下，python内置的有mimetypes module，filetype module，与使用mimetypes库相比，更可靠的方法是使用magic软件包。

magic

magic是libmagic文件标识库的封装，libmagic是一个根据文件头识别文件类型的开发库，因此可以实现对文件类型的判断，在Django上，还可以确保MIME类型与UploadedFile.content_type相匹配。

libmagic

• module name: magic
• pypi: file-magic
• source: https://github.com/file/file/tree/master/python
• man：man libmagic
• install：

  • python setup.py install  # or
    easy_install .           # or
    pip install file-magic　　

• Usage：

  • import magic
    
    detected = magic.detect_from_filename('magic.py')
    print 'Detected MIME type: {}'.format(detected.mime_type)
    print 'Detected encoding: {}'.format(detected.encoding)
    print 'Detected file type name: {}'.format(detected.name)

确定文件mime-type时，选择的工具简称为file,其后端称为libmagic。如果您想将任何libmagic绑定与python一起使用，则需要使用此工具，该工具已经附带了自己的python绑定，称为file-magic。file-magic绑定包含到文件上。如果同时安装文件和python-magic，则python模块将magic引用前者。

python-magic

• module name: magic
• pypi: python-magic
• source: https://github.com/ahupp/python-magic
• install：

  • pip install python-magic #window下依赖python-magic-bin, pip install python-magic-bin

• usage：

  • >>> import magic
    >>> magic.from_file("testdata/test.pdf")
    'PDF document, version 1.2'
    # recommend using at least the first 2048 bytes, as less can produce incorrect identification
    >>> magic.from_buffer(open("testdata/test.pdf").read(2048)) 
    'PDF document, version 1.2'
    >>> magic.from_file("testdata/test.pdf", mime=True)
    'application/pdf'
    

    >>> f = magic.Magic(uncompress=True)
    >>> f.from_file('testdata/test.gz')
    'ASCII text (gzip compressed data, was "test", last modified: Sat Jun 28
    21:32:52 2008, from Unix)'

    >>> f = magic.Magic(mime=True, uncompress=True)
    >>> f.from_file('testdata/test.gz')
    'text/plain'

filemagic

• module name: magic
• pypi: filemagic
• source: https://github.com/aliles/filemagic
• install：

  • pip install filemagic

      这个库与file-magic有一些相似之处，包含在libmagic。

 python-magic用例

import magic

file_type = magic.from_buffer(open("file_types/Bs.tar.gz",'rb').read(2048)) #1
#or
file_type = magic.from_file("file_types/Bs.tar.gz", mime=True) #2

f = magic.Magic(uncompress=True)
ff=f.from_file('file_types/Bs.tar.gz') #3

print(file_type,ff)   #gzip compressed data, last modified: Tue Dec 10 08:46:57 2019, from Unix

　　 我更喜欢的是Magic方法，Magic是libmagic C库的包装。更强大更直接，包含magic的数据库方法，并且可以进行mime_encoding检测。

        但有网友友情提示说不建议用于一般用途，特别是跨多个线程共享并不安全，如果尝试这样做会失败。这个还没深究，但是我们可以先了解magic对Magic方法的调用：

def _get_magic_type(mime):
    i = _instances.get(mime)
    if i is None:
        i = _instances[mime] = Magic(mime=mime)
    return i

　　可以看到，如果magic方法没有获取到mime，还调用了Magic，所以对于安全性和可行性，我们打个问号，等菜鸟我修炼一段时间，攒点经验值，再回来研究研究吧。  

try:
    ms = magic.open(magic.MAGIC_NONE)
    ms.load()
except:
    ms = None

　　magic的一些常量：

MAGIC_NONE = 0x000000 # No flags
MAGIC_DEBUG = 0x000001 # Turn on debugging
MAGIC_SYMLINK = 0x000002 # Follow symlinks
MAGIC_COMPRESS = 0x000004 # Check inside compressed files
MAGIC_DEVICES = 0x000008 # Look at the contents of devices
MAGIC_MIME = 0x000010 # Return a mime string
MAGIC_MIME_ENCODING = 0x000400 # Return the MIME encoding
MAGIC_CONTINUE = 0x000020 # Return all matches
MAGIC_CHECK = 0x000040 # Print warnings to stderr
MAGIC_PRESERVE_ATIME = 0x000080 # Restore access time on exit
MAGIC_RAW = 0x000100 # Don't translate unprintable chars
MAGIC_ERROR = 0x000200 # Handle ENOENT etc as real errors

MAGIC_NO_CHECK_COMPRESS = 0x001000 # Don't check for compressed files
MAGIC_NO_CHECK_TAR = 0x002000 # Don't check for tar files
MAGIC_NO_CHECK_SOFT = 0x004000 # Don't check magic entries
MAGIC_NO_CHECK_APPTYPE = 0x008000 # Don't check application type
MAGIC_NO_CHECK_ELF = 0x010000 # Don't check for elf details
MAGIC_NO_CHECK_ASCII = 0x020000 # Don't check for ascii files
MAGIC_NO_CHECK_TROFF = 0x040000 # Don't check ascii/troff
MAGIC_NO_CHECK_FORTRAN = 0x080000 # Don't check ascii/fortran
MAGIC_NO_CHECK_TOKENS = 0x100000 # Don't check ascii/tokens

分享文章：

cuckoo里的文件识别功能：https://www.cnblogs.com/viwilla/p/5051896.html

对文件格式的判断代码

def _get_filetype(self, data):
        """Gets filetype, uses libmagic if available.
        @param data: data to be analyzed.
        @return: file type or None.
        """
        if not HAVE_MAGIC:
            return None

        try:
            ms = magic.open(magic.MAGIC_NONE)
            ms.load()
            file_type = ms.buffer(data)
        except:
            try:
                file_type = magic.from_buffer(data)
            except Exception:
                return None
        finally:
            try:
                ms.close()
            except:
                pass

        return file_type

　分享找到的一个挺好的用例：https://www.cnblogs.com/17bdw/p/10042549.html

参考链接：https://stackoverflow.com/questions/43580/how-to-find-the-mime-type-of-a-file-in-python