284 lines
12 KiB
Python
284 lines
12 KiB
Python
#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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"""
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A pure Python GIF metadata extractor.
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Supports adjustable detail to fine-tune performance.
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Example code and full epydoc docstrings included.
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Uses:
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- Identifying whether a GIF is static or animated.
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- Extracting the dimensions, pixel aspect ratio, number of frames, loop count,
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global palette or palette size, and background color.
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- Extracting comments and other plaintext.
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- Testing for various structural errors.
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TODO:
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- Provide basic support for XMP Metadata extraction
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- http://en.wikipedia.org/wiki/Extensible_Metadata_Platform#Location_in_file_types
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- http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp
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- Generate test GIF with http://code.google.com/p/python-xmp-toolkit/
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Changelog:
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- 0.2.2: Audited the code and made some corrections.
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- 0.2.1: 40% speed improvement (went from 15 to 9 seconds for 1000 images)
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- 0.2.0: Feature-complete
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- 0.1.0: Initial release
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"""
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__appname__ = "gif.py"
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__author__ = "Stephan Sokolow (deitarion/SSokolow)"
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__version__ = "0.2.2"
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__license__ = "PSF License 2.4 or higher (The Python License)"
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#{ Check Types (enum, numerical ordering is significant)
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CHECK_IS_GIF_FILE = 0 #: Just check for a valid GIF header.
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CHECK_IS_ANIMATED = 1 #: Check whether the file has more than one frame.
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CHECK_COUNT_FRAMES = 2 #: Count the number of frames in the file.
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CHECK_PARSE_PALETTE = 3 #: Parse the palette and resolve the background color.
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CHECK_READ_COMMENTS = 4 #: Load comments (can sometimes be large) into the L{GifInfo} object.
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CHECK_READ_ALL_TEXT = 5 #: Also load the contents of Plain Text extension blocks.
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CHECK_ALL = CHECK_READ_ALL_TEXT #: alias to allow for future modifications
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#{ Warning Codes (bitfield)
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WARN_NONE = 0 #: No warnings
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WARN_BAD_IMG = 1 #: Corruption (of the [sub]block size field(s)) or truncation detected in an image block
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WARN_BAD_EXT = 2 #: Corruption (of the [sub]block size field(s)) or truncation detected in an extension block
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WARN_BAD_SIZE = 4 #: An image block specifies dimensions exceeding the global canvas size
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WARN_BAD_BGCOLOR = 8 #: The background color index specified is greater than the palette size
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WARN_EOF = 16 #: File is missing it's trailer. (Corrupt elsewhere, truncated, or breaking spec by using EOF as the terminator.)
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WARN_TRUNC = 32 #: File is definitively either truncated or corrupt. (An EOF was encountered part-way through a structure.)
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WARN_LOOP_POS = 64 #: Netscape Application Extension block (animation-control) was present but not first in the file.
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#}
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import struct
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#{ Structures used by GifInfo
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gifHeaderStruct = struct.Struct('<xxxxxxHHBBB') #: File header
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gifImageStruct = struct.Struct('<HHHHB') #: Image block header
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gifExtenStruct = struct.Struct('<BB') #: Top-level extension block header
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gifNetscapeStruct = struct.Struct('<BBH') #: NETSCAPE Loop-control sub-block
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gifColorTripleStruct = struct.Struct('<BBB') #: RGB palette element
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gifPlaintextStruct = struct.Struct('<BHHHHBBBB') #: Plain Text block header
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#}
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class BadHeaderException(Exception):
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"""Raised when no valid GIF header is found"""
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class GifInfo(object):
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"""A class for loading and storing metadata from GIF files.
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Accepts paths and file-like objects.
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When using L{CHECK_ALL}, this can also be used to walk past a valid
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GIF file in an un-delimited byte stream in order to identify the point at
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which the following file starts. (It doesn't C{fh.seek(0)} or C{fh.close()} after
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use)
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"""
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warnFlags = WARN_NONE #: A bit field of C{WARN_*} flags set by L{__init__}
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checkLevel = CHECK_ALL #: Default C{CHECK_*} level used by L{__init__}
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#{ Pre-defined "unset" values for GIF Metadata
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path = None #: The path to the file, if one was passed to L{__init__}
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version = None #: C{87a} or C{89a}
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width = None
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height = None
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loopCount = None
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pixelAspect = None
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paletteSize = None #: Always calculated if a global palette is present
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palette = None #: The palette as a list of integer RGB tuples. Requires L{CHECK_PARSE_PALETTE}.
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bgColor = None #: Global background color as an RGB tuple. Requires L{CHECK_PARSE_PALETTE}.
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comments = None #: Text in Comment (0xFE) extension blocks as a list of strings. Requires L{CHECK_READ_COMMENTS}
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otherText = None #: Text in "Plain Text" (0x01) extension blocks as a list of strings. Requires L{CHECK_READ_ALL_TEXT}
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frameCount = 0
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#}
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def __init__(self, fh, checkLevel=checkLevel):
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"""
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@param fh: A path or file-like object for a GIF file.
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@param checkLevel: A C{CHECK_*} constant.
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@raises BadHeaderException: The given file lacks a valid GIF header.
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@raises IOError: The underlying C{open()} system call failed.
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"""
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self.checkLevel = checkLevel
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if isinstance(fh, basestring):
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self.path = fh
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fh = open(fh, 'rb')
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header = fh.read(gifHeaderStruct.size)
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if len(header) < gifHeaderStruct.size:
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raise BadHeaderException("File is too small to be a GIF")
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self.version = header[3:6]
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if header[0:3] != 'GIF' or self.version not in ['87a', '89a']:
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raise BadHeaderException("File does not have a recognizable GIF header")
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elif self.checkLevel <= CHECK_IS_GIF_FILE:
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return
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self.width, self.height, GCTF_Byte, bgColor, self.pixelAspect = gifHeaderStruct.unpack(header)
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if self.pixelAspect:
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self.pixelAspect = (self.pixelAspect + 15) / 64.0
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rawPalette = self._getPalette(fh, GCTF_Byte)
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self.paletteSize = int(len(rawPalette) / 3)
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if self.checkLevel >= CHECK_PARSE_PALETTE:
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self.palette = []
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for pos in range(0, self.paletteSize):
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self.palette.append(gifColorTripleStruct.unpack_from(rawPalette, pos * 3))
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if self.paletteSize and bgColor > self.paletteSize:
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self.warnFlags = self.warnFlags | WARN_BAD_BGCOLOR
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elif self.palette:
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self.bgColor = self.palette[bgColor]
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# Iterate blocks
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self.firstBlock = True
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blocktype = self._read(fh, 1)
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while not blocktype == chr(0x3B) and not self.warnFlags & WARN_EOF:
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self._blockHandlers.get(blocktype, lambda x, y:'')(self, fh)
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if self.checkLevel <= CHECK_IS_ANIMATED and self.frameCount > 1:
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return
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self.firstBlock = False
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blocktype = self._read(fh, 1)
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del self.firstBlock
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def _handleImageBlock(self, fh):
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""""""
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self.frameCount += 1
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try:
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x, y, w, h, LCTF_Byte = gifImageStruct.unpack(self._read(fh, gifImageStruct.size))
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except:
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self.warnFlags = self.warnFlags | WARN_EOF | WARN_TRUNC
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return
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if x + w > self.width or y + h > self.height:
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self.warnFlags = self.warnFlags | WARN_BAD_SIZE
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self._getPalette(fh, LCTF_Byte) # Skip the local color table if present
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fh.read(1) # Skip the LZW minimum code size.
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# Skip content and test for the block terminator
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if not self._skipSubBlocks(fh): # For example, if it's a zero-length string like EOF would return.
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self.warnFlags = self.warnFlags | WARN_BAD_IMG
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def _handleGenericExtensionBlock(self, fh):
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"""@todo: Rewrite this so extension block types have method handlers."""
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try:
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extType, blkSize = gifExtenStruct.unpack(self._read(fh, gifExtenStruct.size))
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except:
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self.warnFlags = self.warnFlags | WARN_EOF | WARN_TRUNC
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return
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startOffset = fh.tell()
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if extType == 0x01 and self.checkLevel >= CHECK_READ_ALL_TEXT: # Plain Text Block
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self._read(fh, gifPlaintextStruct.size)
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self.otherText = self.otherText or []
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blkSize = self._read(fh, 1)
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while blkSize and blkSize != '\x00':
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self.otherText.append(self._read(fh, ord(blkSize)))
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blkSize = self._read(fh, 1)
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elif extType == 0xFE and self.checkLevel >= CHECK_READ_COMMENTS: # Comment Block
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self.comments = self.comments or []
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blkSize = self._read(fh, 1)
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while blkSize and blkSize != '\x00':
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self.comments.append(self._read(fh, ord(blkSize)))
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blkSize = self._read(fh, 1)
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elif extType == 0xFF: # Application Block
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if blkSize == 0x0B and self._read(fh, blkSize) == "NETSCAPE2.0":
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try:
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a, b, self.loopCount = gifNetscapeStruct.unpack(self._read(fh, gifNetscapeStruct.size))
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except:
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self.warnFlags = self.warnFlags | WARN_EOF | WARN_TRUNC
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return
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if a != 3 and b != 1:
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self.warnFlags = self.warnFlags | WARN_BAD_EXT
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if not self.firstBlock:
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self.warnFlags = self.warnFlags | WARN_LOOP_POS
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else:
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fh.seek( startOffset + blkSize ) # Skip the contents
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# Test for the block terminator
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if not self._skipSubBlocks(fh):
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self.warnFlags = self.warnFlags | WARN_BAD_EXT
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def _getPalette(self, handle, bitfield):
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"""Using the size value from C{bitfield},
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load the palette at C{handle}'s current file pointer position."""
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if bitfield & int("10000000", 2):
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nBits = bitfield & int("00000111", 2)
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tableSize = 3 * 2**( nBits + 1 )
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return handle.read(tableSize)
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else:
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return ''
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def _read(self, handle, size):
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"""Attempt to read the specified number of bytes. Set L{WARN_EOF} if
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fewer are received."""
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content = handle.read(size)
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if len(content) < size:
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self.warnFlags = self.warnFlags | WARN_EOF
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return content
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def _skipSubBlocks(self, handle):
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"""Skip sub-blocks beginning at the current file pointer position
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using fseek."""
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offset = handle.tell()
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blkSize = handle.read(1)
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while blkSize and blkSize != '\x00':
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offset += ord(blkSize) + 1
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handle.seek(offset)
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blkSize = handle.read(1)
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return blkSize
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_blockHandlers = {
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chr(0x2C) : _handleImageBlock,
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chr(0x21) : _handleGenericExtensionBlock,
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}
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def gif_is_animated(path):
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"""A simple convenience function for testing whether a GIF is animated.
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@rtype: C{bool}
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"""
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return GifInfo(file(path,'rb'), CHECK_IS_ANIMATED).frameCount > 1
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if __name__ == '__main__':
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from optparse import OptionParser
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parser = OptionParser(description=__doc__.split('\n\n')[0],
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version="%%prog v%s" % __version__, usage="%prog <path> ...")
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opts, args = parser.parse_args()
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if args:
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for fpath in args:
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try:
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info = GifInfo(fpath, CHECK_COUNT_FRAMES)
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warnFlags = (
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(info.warnFlags & WARN_BAD_IMG and 'I' or ' ') +
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(info.warnFlags & WARN_BAD_EXT and 'X' or ' ') +
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(info.warnFlags & WARN_BAD_SIZE and 'C' or ' ') +
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(info.warnFlags & WARN_BAD_BGCOLOR and 'B' or ' ') +
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(info.warnFlags & WARN_EOF and 'E' or ' ') +
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(info.warnFlags & WARN_TRUNC and 'T' or ' ') +
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(info.warnFlags & WARN_LOOP_POS and 'L' or ' ')
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)
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print "[%s](%3s Frames): %s" % (warnFlags, info.frameCount, info.path)
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except BadHeaderException, err:
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print "%s: %s" % (str(err), fpath)
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print "\nWarning Flags:"
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print " I = Image Chunk Corruption/Truncation"
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print " X = Extension Chunk Corruption/Truncation"
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print " C = Image Chunk Dimensions Exceed Global Canvas"
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print " B = Bad Background Color (Index Exceeds Palette Size)"
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print " E = Unexpected EOF Encountered (Missing Image Terminator)"
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print " T = EOF Encountered Within A Block Header (Corrupt or Truncated File)"
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print " L = Loop-control block misplaced within the file"
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print
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print "Note: A nearly-threefold speed-up can be had by using CHECK_IS_ANIMATED rather than CHECK_COUNT_FRAMES"
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