Mercurial > cpython-lru_cache-weakref

annotate Lib/struct.py @ 39940:dfd809dcf680 2.5

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Bug #1446043: correctly raise a LookupError if an encoding name given to encodings.search_function() contains a dot. (backport from rev. 52075)
author Georg Brandl <georg@python.org>
date Sat, 30 Sep 2006 11:22:35 +0000
parents 4aed4367add2
children 8d69edd3d290
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 """
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2 Functions to convert between Python values and C structs.
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3 Python strings are used to hold the data representing the C struct
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4 and also as format strings to describe the layout of data in the C struct.
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5
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6 The optional first format char indicates byte order, size and alignment:
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7 @: native order, size & alignment (default)
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8 =: native order, std. size & alignment
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9 <: little-endian, std. size & alignment
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10 >: big-endian, std. size & alignment
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11 !: same as >
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12
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13 The remaining chars indicate types of args and must match exactly;
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14 these can be preceded by a decimal repeat count:
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15 x: pad byte (no data); c:char; b:signed byte; B:unsigned byte;
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16 h:short; H:unsigned short; i:int; I:unsigned int;
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17 l:long; L:unsigned long; f:float; d:double.
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18 Special cases (preceding decimal count indicates length):
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19 s:string (array of char); p: pascal string (with count byte).
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20 Special case (only available in native format):
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21 P:an integer type that is wide enough to hold a pointer.
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22 Special case (not in native mode unless 'long long' in platform C):
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23 q:long long; Q:unsigned long long
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24 Whitespace between formats is ignored.
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25
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26 The variable struct.error is an exception raised on errors.
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27 """
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28 __version__ = '0.1'
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29
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30 from _struct import Struct, error
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31
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32 _MAXCACHE = 100
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33 _cache = {}
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34
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35 def _compile(fmt):
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36 # Internal: compile struct pattern
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37 if len(_cache) >= _MAXCACHE:
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38 _cache.clear()
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39 s = Struct(fmt)
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40 _cache[fmt] = s
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41 return s
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42
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43 def calcsize(fmt):
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44 """
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45 Return size of C struct described by format string fmt.
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46 See struct.__doc__ for more on format strings.
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47 """
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48 try:
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49 o = _cache[fmt]
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50 except KeyError:
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51 o = _compile(fmt)
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52 return o.size
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53
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54 def pack(fmt, *args):
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55 """
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56 Return string containing values v1, v2, ... packed according to fmt.
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57 See struct.__doc__ for more on format strings.
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58 """
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59 try:
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60 o = _cache[fmt]
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61 except KeyError:
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62 o = _compile(fmt)
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63 return o.pack(*args)
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64
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65 def pack_into(fmt, buf, offset, *args):
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66 """
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67 Pack the values v1, v2, ... according to fmt, write
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68 the packed bytes into the writable buffer buf starting at offset.
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69 See struct.__doc__ for more on format strings.
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70 """
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71 try:
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72 o = _cache[fmt]
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73 except KeyError:
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74 o = _compile(fmt)
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75 return o.pack_into(buf, offset, *args)
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76
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77 def unpack(fmt, s):
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78 """
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79 Unpack the string, containing packed C structure data, according
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80 to fmt. Requires len(string)==calcsize(fmt).
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81 See struct.__doc__ for more on format strings.
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82 """
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83 try:
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84 o = _cache[fmt]
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85 except KeyError:
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86 o = _compile(fmt)
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87 return o.unpack(s)
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88
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89 def unpack_from(fmt, buf, offset=0):
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90 """
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91 Unpack the buffer, containing packed C structure data, according to
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92 fmt starting at offset. Requires len(buffer[offset:]) >= calcsize(fmt).
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93 See struct.__doc__ for more on format strings.
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94 """
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95 try:
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96 o = _cache[fmt]
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97 except KeyError:
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98 o = _compile(fmt)
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99 return o.unpack_from(buf, offset)