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|
"""Provides objects that can characterize image streams.
That characterization is as to content type and size, as a required step in including
them in a document.
"""
from __future__ import annotations
import hashlib
import io
import os
from typing import IO, Tuple
from docx.image.exceptions import UnrecognizedImageError
from docx.shared import Emu, Inches, Length, lazyproperty
class Image:
"""Graphical image stream such as JPEG, PNG, or GIF with properties and methods
required by ImagePart."""
def __init__(self, blob: bytes, filename: str, image_header: BaseImageHeader):
super(Image, self).__init__()
self._blob = blob
self._filename = filename
self._image_header = image_header
@classmethod
def from_blob(cls, blob: bytes) -> Image:
"""Return a new |Image| subclass instance parsed from the image binary contained
in `blob`."""
stream = io.BytesIO(blob)
return cls._from_stream(stream, blob)
@classmethod
def from_file(cls, image_descriptor: str | IO[bytes]):
"""Return a new |Image| subclass instance loaded from the image file identified
by `image_descriptor`, a path or file-like object."""
if isinstance(image_descriptor, str):
path = image_descriptor
with open(path, "rb") as f:
blob = f.read()
stream = io.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) -> str:
"""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) -> int:
"""The horizontal pixel dimension of the image."""
return self._image_header.px_width
@property
def px_height(self) -> int:
"""The vertical pixel dimension of the image."""
return self._image_header.px_height
@property
def horz_dpi(self) -> int:
"""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) -> int:
"""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) -> Inches:
"""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) -> Inches:
"""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: int | Length | None = None, height: int | Length | None = None
) -> Tuple[Length, Length]:
"""(cx, cy) pair representing scaled dimensions of this image.
The native dimensions of the image are scaled by applying the following rules to
the `width` and `height` arguments.
* 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:
assert height is not 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: IO[bytes],
blob: bytes,
filename: str | None = None,
) -> Image:
"""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: IO[bytes]):
"""A |BaseImageHeader| subclass instance that can parse headers of image in `stream`."""
from docx.image import SIGNATURES
def read_32(stream: IO[bytes]):
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:
"""Base class for image header subclasses like |Jpeg| and |Tiff|."""
def __init__(self, px_width: int, px_height: int, horz_dpi: int, vert_dpi: int):
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) -> str:
"""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) -> str:
"""Default filename extension for images of this type.
An abstract property definition, must be implemented by all subclasses.
"""
raise NotImplementedError(
"default_ext property must be implemented by all subclasses of " "BaseImageHeader"
)
@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
|
