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55 lines
1.8 KiB
Python
55 lines
1.8 KiB
Python
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from hachoir.field import FieldSet, ParserError
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class StaticFieldSet(FieldSet):
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"""
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Static field set: format class attribute is a tuple of all fields
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in syntax like:
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format = (
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(TYPE1, ARG1, ARG2, ...),
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(TYPE2, ARG1, ARG2, ..., {KEY1=VALUE1, ...}),
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...
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)
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Types with dynamic size are forbidden, eg. CString, PascalString8, etc.
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"""
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format = None # You have to redefine this class variable
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_class = None
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def __new__(cls, *args, **kw):
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assert cls.format is not None, "Class attribute 'format' is not set"
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if cls._class is not cls.__name__:
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cls._class = cls.__name__
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cls.static_size = cls._computeStaticSize()
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return object.__new__(cls)
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@staticmethod
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def _computeItemSize(item):
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item_class = item[0]
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if item_class.static_size is None:
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raise ParserError("Unable to get static size of field type: %s"
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% item_class.__name__)
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if callable(item_class.static_size):
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if isinstance(item[-1], dict):
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return item_class.static_size(*item[1:-1], **item[-1])
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else:
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return item_class.static_size(*item[1:])
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else:
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assert isinstance(item_class.static_size, int)
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return item_class.static_size
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def createFields(self):
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for item in self.format:
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if isinstance(item[-1], dict):
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yield item[0](self, *item[1:-1], **item[-1])
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else:
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yield item[0](self, *item[1:])
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@classmethod
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def _computeStaticSize(cls, *args):
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return sum(cls._computeItemSize(item) for item in cls.format)
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# Initial value of static_size, it changes when first instance
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# is created (see __new__)
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static_size = _computeStaticSize
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