patch #1493701: performance enhancements for struct module

Lib/struct.py

+"""
+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 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)
+