99 lines
2.9 KiB
Python
99 lines
2.9 KiB
Python
"""
|
|
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_into(fmt, buf, offset, *args):
|
|
"""
|
|
Pack the values v1, 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_into(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)
|