Monkey patch for python-docx to enable EMF support

docx_emf_patch.py

# encoding: utf-8
# This module monkey patches the docx library to add support for Windows Enhanced Metafile images (EMF)
# Put in a local folder and "import docx_emf_patch" to enable EMF support.

from __future__ import absolute_import, division, print_function

import docx
from docx.image.exceptions import UnrecognizedImageError
from docx.image.constants import MIME_TYPE
from docx.image.exceptions import InvalidImageStreamError
from docx.image.helpers import BIG_ENDIAN, StreamReader
from docx.image.image import BaseImageHeader
import struct


def _ImageHeaderFactory(stream):
    """
    Return a |BaseImageHeader| subclass instance that knows how to parse the
    headers of the image in *stream*.
    """
    from docx.image import SIGNATURES

    def read_64(stream):
        stream.seek(0)
        return stream.read(64)

    header = read_64(stream)
    for cls, offset, signature_bytes in SIGNATURES:
        end = offset + len(signature_bytes)
        found_bytes = header[offset:end]
        if found_bytes == signature_bytes:
            return cls.from_stream(stream)
    raise UnrecognizedImageError


class Emf(BaseImageHeader):
    """
    Image header parser for EMF images
    """
    @property
    def content_type(self):
        """
        MIME content type for this image, unconditionally `image/emf` for
        EMF images.
        """
        return MIME_TYPE.EMF

    @property
    def default_ext(self):
        """
        Default filename extension, always 'emf' for EMF images.
        """
        return 'emf'

    @classmethod
    def from_stream(cls, stream,filename=None):
        """
        Return a |Emf| instance having header properties parsed from image in
        *stream*.
        """

        """
        @0 DWORD iType; // fixed
        @4 DWORD nSize; // var
        @8 RECTL rclBounds;
        @24 RECTL rclFrame; // .01 millimeter units L T R B
        @40 DWORD dSignature; // ENHMETA_SIGNATURE = 0x464D4520
        DWORD nVersion;
        DWORD nBytes;
        DWORD nRecords;
        WORD  nHandles;
        WORD  sReserved;
        DWORD nDescription;
        DWORD offDescription;
        DWORD nPalEntries;
        SIZEL szlDevice;
        SIZEL szlMillimeters;
        """
        stream.seek(0)
        x = stream.read(40)
        stream.seek(0)
        iType,nSize = struct.unpack("ii",x[0:8])
        rclBounds = struct.unpack("iiii",x[8:24])
        rclFrame = struct.unpack("iiii",x[24:40])

        dpi = 300
        horz_dpi = dpi
        vert_dpi = dpi
        mmwidth = (rclFrame[2]-rclFrame[0])/100.0
        mmheight = (rclFrame[3]-rclFrame[1])/100.0
        px_width = int(mmwidth*dpi*0.03937008)
        px_height = int(mmheight*dpi*0.03937008)

        #1 dot/inch  =  0.03937008 pixel/millimeter
        return cls(px_width,px_height,horz_dpi,vert_dpi)


docx.image.Emf = Emf
docx.image.constants.MIME_TYPE.EMF = 'image/emf'
docx.image.SIGNATURES = tuple(list(docx.image.SIGNATURES) + [(Emf,  40, b' EMF')])
docx.image.image._ImageHeaderFactory = _ImageHeaderFactory