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from struct import Struct
from .constants import MIME_TYPE
from .image import BaseImageHeader
class Gif(BaseImageHeader):
"""Image header parser for GIF images.
Note that the GIF format does not support resolution (DPI) information. Both
horizontal and vertical DPI default to 72.
"""
@classmethod
def from_stream(cls, stream):
"""Return |Gif| instance having header properties parsed from GIF image in
`stream`."""
px_width, px_height = cls._dimensions_from_stream(stream)
return cls(px_width, px_height, 72, 72)
@property
def content_type(self):
"""MIME content type for this image, unconditionally `image/gif` for GIF
images."""
return MIME_TYPE.GIF
@property
def default_ext(self):
"""Default filename extension, always 'gif' for GIF images."""
return "gif"
@classmethod
def _dimensions_from_stream(cls, stream):
stream.seek(6)
bytes_ = stream.read(4)
struct = Struct("<HH")
px_width, px_height = struct.unpack(bytes_)
return px_width, px_height
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