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103 lines
3 KiB
Python
103 lines
3 KiB
Python
"""
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Functions to convert between Python values and C structs.
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Python strings are used to hold the data representing the C struct
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and also as format strings to describe the layout of data in the C struct.
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The optional first format char indicates byte order, size and alignment:
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@: native order, size & alignment (default)
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=: native order, std. size & alignment
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<: little-endian, std. size & alignment
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>: big-endian, std. size & alignment
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!: same as >
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The remaining chars indicate types of args and must match exactly;
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these can be preceded by a decimal repeat count:
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x: pad byte (no data); c:char; b:signed byte; B:unsigned byte;
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h:short; H:unsigned short; i:int; I:unsigned int;
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l:long; L:unsigned long; f:float; d:double.
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Special cases (preceding decimal count indicates length):
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s:string (array of char); p: pascal string (with count byte).
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Special case (only available in native format):
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P:an integer type that is wide enough to hold a pointer.
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Special case (not in native mode unless 'long long' in platform C):
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q:long long; Q:unsigned long long
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Whitespace between formats is ignored.
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The variable struct.error is an exception raised on errors.
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"""
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# XXX Move the bytes and str8 casts into the _struct module
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__version__ = '3.0'
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from _struct import Struct, error
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_MAXCACHE = 100
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_cache = {}
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def _compile(fmt):
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# Internal: compile struct pattern
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if len(_cache) >= _MAXCACHE:
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_cache.clear()
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s = Struct(str8(fmt))
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_cache[fmt] = s
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return s
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def calcsize(fmt):
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"""
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Return size of C struct described by format string fmt.
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See struct.__doc__ for more on format strings.
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"""
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try:
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o = _cache[fmt]
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except KeyError:
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o = _compile(fmt)
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return o.size
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def pack(fmt, *args):
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"""
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Return string containing values v1, v2, ... packed according to fmt.
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See struct.__doc__ for more on format strings.
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"""
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try:
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o = _cache[fmt]
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except KeyError:
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o = _compile(fmt)
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return bytes(o.pack(*args))
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def pack_into(fmt, buf, offset, *args):
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"""
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Pack the values v1, v2, ... according to fmt, write
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the packed bytes into the writable buffer buf starting at offset.
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See struct.__doc__ for more on format strings.
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"""
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try:
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o = _cache[fmt]
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except KeyError:
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o = _compile(fmt)
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return bytes(o.pack_into(buf, offset, *args))
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def unpack(fmt, s):
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"""
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Unpack the string, containing packed C structure data, according
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to fmt. Requires len(string)==calcsize(fmt).
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See struct.__doc__ for more on format strings.
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"""
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try:
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o = _cache[fmt]
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except KeyError:
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o = _compile(fmt)
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return o.unpack(s)
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def unpack_from(fmt, buf, offset=0):
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"""
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Unpack the buffer, containing packed C structure data, according to
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fmt starting at offset. Requires len(buffer[offset:]) >= calcsize(fmt).
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See struct.__doc__ for more on format strings.
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"""
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try:
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o = _cache[fmt]
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except KeyError:
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o = _compile(fmt)
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return o.unpack_from(buf, offset)
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