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# encoding: utf-8
"""
Provides objects that can characterize image streams as to content type and
size, as a required step in including them in a document.
"""
from __future__ import absolute_import, division, print_function
import hashlib
import os
from ..compat import BytesIO, is_string
from .exceptions import UnrecognizedImageError
from ..shared import Emu, Inches, lazyproperty
class Image(object):
"""
Graphical image stream such as JPEG, PNG, or GIF with properties and
methods required by ImagePart.
"""
def __init__(self, blob, filename, image_header):
super(Image, self).__init__()
self._blob = blob
self._filename = filename
self._image_header = image_header
@classmethod
def from_blob(cls, blob):
"""
Return a new |Image| subclass instance parsed from the image binary
contained in *blob*.
"""
stream = BytesIO(blob)
return cls._from_stream(stream, blob)
@classmethod
def from_file(cls, image_descriptor):
"""
Return a new |Image| subclass instance loaded from the image file
identified by *image_descriptor*, a path or file-like object.
"""
if is_string(image_descriptor):
path = image_descriptor
with open(path, 'rb') as f:
blob = f.read()
stream = BytesIO(blob)
filename = os.path.basename(path)
else:
stream = image_descriptor
stream.seek(0)
blob = stream.read()
filename = None
return cls._from_stream(stream, blob, filename)
@property
def blob(self):
"""
The bytes of the image 'file'
"""
return self._blob
@property
def content_type(self):
"""
MIME content type for this image, e.g. ``'image/jpeg'`` for a JPEG
image
"""
return self._image_header.content_type
@lazyproperty
def ext(self):
"""
The file extension for the image. If an actual one is available from
a load filename it is used. Otherwise a canonical extension is
assigned based on the content type. Does not contain the leading
period, e.g. 'jpg', not '.jpg'.
"""
return os.path.splitext(self._filename)[1][1:]
@property
def filename(self):
"""
Original image file name, if loaded from disk, or a generic filename
if loaded from an anonymous stream.
"""
return self._filename
@property
def px_width(self):
"""
The horizontal pixel dimension of the image
"""
return self._image_header.px_width
@property
def px_height(self):
"""
The vertical pixel dimension of the image
"""
return self._image_header.px_height
@property
def horz_dpi(self):
"""
Integer dots per inch for the width of this image. Defaults to 72
when not present in the file, as is often the case.
"""
return self._image_header.horz_dpi
@property
def vert_dpi(self):
"""
Integer dots per inch for the height of this image. Defaults to 72
when not present in the file, as is often the case.
"""
return self._image_header.vert_dpi
@property
def width(self):
"""
A |Length| value representing the native width of the image,
calculated from the values of `px_width` and `horz_dpi`.
"""
return Inches(self.px_width / self.horz_dpi)
@property
def height(self):
"""
A |Length| value representing the native height of the image,
calculated from the values of `px_height` and `vert_dpi`.
"""
return Inches(self.px_height / self.vert_dpi)
def scaled_dimensions(self, width=None, height=None):
"""
Return a (cx, cy) 2-tuple representing the native dimensions of this
image scaled by applying the following rules to *width* and *height*.
If both *width* and *height* are specified, the return value is
(*width*, *height*); no scaling is performed. If only one is
specified, it is used to compute a scaling factor that is then
applied to the unspecified dimension, preserving the aspect ratio of
the image. If both *width* and *height* are |None|, the native
dimensions are returned. The native dimensions are calculated using
the dots-per-inch (dpi) value embedded in the image, defaulting to 72
dpi if no value is specified, as is often the case. The returned
values are both |Length| objects.
"""
if width is None and height is None:
return self.width, self.height
if width is None:
scaling_factor = float(height) / float(self.height)
width = round(self.width * scaling_factor)
if height is None:
scaling_factor = float(width) / float(self.width)
height = round(self.height * scaling_factor)
return Emu(width), Emu(height)
@lazyproperty
def sha1(self):
"""
SHA1 hash digest of the image blob
"""
return hashlib.sha1(self._blob).hexdigest()
@classmethod
def _from_stream(cls, stream, blob, filename=None):
"""
Return an instance of the |Image| subclass corresponding to the
format of the image in *stream*.
"""
image_header = _ImageHeaderFactory(stream)
if filename is None:
filename = 'image.%s' % image_header.default_ext
return cls(blob, filename, image_header)
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_32(stream):
stream.seek(0)
return stream.read(32)
header = read_32(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 BaseImageHeader(object):
"""
Base class for image header subclasses like |Jpeg| and |Tiff|.
"""
def __init__(self, px_width, px_height, horz_dpi, vert_dpi):
self._px_width = px_width
self._px_height = px_height
self._horz_dpi = horz_dpi
self._vert_dpi = vert_dpi
@property
def content_type(self):
"""
Abstract property definition, must be implemented by all subclasses.
"""
msg = (
'content_type property must be implemented by all subclasses of '
'BaseImageHeader'
)
raise NotImplementedError(msg)
@property
def default_ext(self):
"""
Default filename extension for images of this type. An abstract
property definition, must be implemented by all subclasses.
"""
msg = (
'default_ext property must be implemented by all subclasses of '
'BaseImageHeader'
)
raise NotImplementedError(msg)
@property
def px_width(self):
"""
The horizontal pixel dimension of the image
"""
return self._px_width
@property
def px_height(self):
"""
The vertical pixel dimension of the image
"""
return self._px_height
@property
def horz_dpi(self):
"""
Integer dots per inch for the width of this image. Defaults to 72
when not present in the file, as is often the case.
"""
return self._horz_dpi
@property
def vert_dpi(self):
"""
Integer dots per inch for the height of this image. Defaults to 72
when not present in the file, as is often the case.
"""
return self._vert_dpi
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