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"""
Functions to convert between Python values and C structs.
Python strings are used to hold the data representing the C struct
and also as format strings to describe the layout of data in the C struct.
The optional first format char indicates byte order, size and alignment:
@: native order, size & alignment (default)
=: native order, std. size & alignment
<: little-endian, std. size & alignment
>: big-endian, std. size & alignment
!: same as >
The remaining chars indicate types of args and must match exactly;
these can be preceded by a decimal repeat count:
x: pad byte (no data); c:char; b:signed byte; B:unsigned byte;
h:short; H:unsigned short; i:int; I:unsigned int;
l:long; L:unsigned long; f:float; d:double.
Special cases (preceding decimal count indicates length):
s:string (array of char); p: pascal string (with count byte).
Special case (only available in native format):
P:an integer type that is wide enough to hold a pointer.
Special case (not in native mode unless 'long long' in platform C):
q:long long; Q:unsigned long long
Whitespace between formats is ignored.
The variable struct.error is an exception raised on errors.
"""
__version__ = '0.1'
from _struct import Struct, error
_MAXCACHE = 100
_cache = {}
def _compile(fmt):
# Internal: compile struct pattern
if len(_cache) >= _MAXCACHE:
_cache.clear()
s = Struct(fmt)
_cache[fmt] = s
return s
def calcsize(fmt):
"""
Return size of C struct described by format string fmt.
See struct.__doc__ for more on format strings.
"""
try:
o = _cache[fmt]
except KeyError:
o = _compile(fmt)
return o.size
def pack(fmt, *args):
"""
Return string containing values v1, v2, ... packed according to fmt.
See struct.__doc__ for more on format strings.
"""
try:
o = _cache[fmt]
except KeyError:
o = _compile(fmt)
return o.pack(*args)
def pack_to(fmt, buf, offset, *args):
"""
Pack the values v2, v2, ... according to fmt, write
the packed bytes into the writable buffer buf starting at offset.
See struct.__doc__ for more on format strings.
"""
try:
o = _cache[fmt]
except KeyError:
o = _compile(fmt)
return o.pack_to(buf, offset, *args)
def unpack(fmt, s):
"""
Unpack the string, containing packed C structure data, according
to fmt. Requires len(string)==calcsize(fmt).
See struct.__doc__ for more on format strings.
"""
try:
o = _cache[fmt]
except KeyError:
o = _compile(fmt)
return o.unpack(s)
def unpack_from(fmt, buf, offset=0):
"""
Unpack the buffer, containing packed C structure data, according to
fmt starting at offset. Requires len(buffer[offset:]) >= calcsize(fmt).
See struct.__doc__ for more on format strings.
"""
try:
o = _cache[fmt]
except KeyError:
o = _compile(fmt)
return o.unpack_from(buf, offset)
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