"""

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)