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数学之路-python计算实战(4)-Lempel-Ziv压缩(2)
Format characters have the following meaning; the conversion between C and Python values should be obvious given their types. The ‘Standard size’ column refers to the size of the packed value in bytes when using standard size; that is, when the format string starts with one of ‘<‘, ‘>‘, ‘!‘ or ‘=‘. When using native size, the size of the packed value is platform-dependent.
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http://blog.csdn.net/myhaspl/
Format | C Type | Python type | Standard size | Notes |
---|---|---|---|---|
x | pad byte | no value | ||
c | char | string of length 1 | 1 | |
b | signed char | integer | 1 | (3) |
B | unsigned char | integer | 1 | (3) |
? | _Bool | bool | 1 | (1) |
h | short | integer | 2 | (3) |
H | unsigned short | integer | 2 | (3) |
i | int | integer | 4 | (3) |
I | unsigned int | integer | 4 | (3) |
l | long | integer | 4 | (3) |
L | unsigned long | integer | 4 | (3) |
q | long long | integer | 8 | (2), (3) |
Q | unsigned long long | integer | 8 | (2), (3) |
f | float | float | 4 | (4) |
d | double | float | 8 | (4) |
s | char[] | string | ||
p | char[] | string | ||
P | void * | integer | (5), (3) |
Return a string containing the values v1, v2, ... packed according to the given format. The arguments must match the values required by the format exactly.
Unpack the string (presumably packed by pack(fmt, ...)) according to the given format. The result is a tuple even if it contains exactly one item. The string must contain exactly the amount of data required by the format (len(string) must equal calcsize(fmt)).
# -*- coding: utf-8 -*- #lempel-ziv算法 #code:myhaspl@myhaspl.com import struct mystr="" print "\n读取源文件".decode("utf8") mytextfile= open(‘test2.txt‘,‘r‘) try: mystr=mytextfile.read( ) finally: mytextfile.close() my_str=mystr #码表 codeword_dictionary={} #待压缩文本长度 str_len=len(my_str) #码字最大长度 dict_maxlen=1 #将解析文本段的位置(下一次解析文本的起点) now_index=0 #码表的最大索引 max_index=0 #压缩后数据 print "\n生成压缩数据中".decode("utf8") compresseddata=http://www.mamicode.com/[]"don‘t find the Code word,add Code word:%s index:%d"%(my_str[now_index:now_index+mystep],max_index) else: #找到码字,添加新的码字 max_index+=1 if now_index+mystep+1<=str_len: codeword_dictionary[my_str[now_index:now_index+mystep+1]]=max_index if mystep+1>dict_maxlen: dict_maxlen=mystep+1 print "find the Code word:%s add Code word:%s index:%d"%(my_str[now_index:now_index+now_len],my_str[now_index:now_index+mystep+1],max_index) ....... ...... my_codeword_dictionary[my_maxindex]=my_codeword_dictionary[cwkey]+cwlaster uncompressdata.append(my_codeword_dictionary[cwkey]) uncompressdata.append(cwlaster) print ".", uncompress_str=uncompress_str.join(uncompressdata) uncompressstr=uncompress_str print "\n将解压结果写入文件里..\n".decode("utf8") uncompress_file= open(‘uncompress.txt‘,‘w‘) try: uncompress_file.write(uncompressstr) print "\n解压成功,已解压到uncompress.txt!\n".decode("utf8") finally: uncompress_file.close()
以下对中文维基中对python的解释文本进行压缩:
调用该程序先压缩形成压缩文件,然后打开压缩文件解压
$ pypy lempel-ziv-compress.py python.txt python.lzv
………………..
find the Code word: C add Code word: CP index:9938
index:9939de word:ython add Code word:ython
find the Code word:
^ add Code word:
^ h index:9940
find the Code word:ttp add Code word:ttp: index:9941
find the Code word:// add Code word://e index:9942
find the Code word:dit add Code word:ditr index:9943
find the Code word:a. add Code word:a.o index:9944
生成压缩数据头部
将压缩数据写入压缩文件里
…………….
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将解压结果写入文件里..
解压成功,已解压到uncompress.txt!
查看压缩效果:
$ ls -l -h
…………….
-rw-rw-r-- 1 deep deep 5.0K Jul 1 20:55 lempel-ziv-compress.py
-rw-rw-r-- 1 deep deep 30K Jul 1 20:55 python.lzv
-rw-rw-r-- 1 deep deep 36K Jul 1 20:57 python.txt
-rw-rw-r-- 1 deep deep 36K Jul 1 20:55 uncompress.txt从上面显示结果能够看到,没压缩前为36K,压缩后为30k
压缩sqlite 3.8.5的所有源代码
$ pypy lempel-ziv-compress.py sqlitesrc.txtsqlitesrc.lzv
查看压缩效果:
$ ls -l -h
…………….
-rw-rw-r-- 1 deep deep 3.2M Jul 1 21:18 sqlitesrc.lzv
-rw-rw-r-- 1 deep deep 5.2M Jul 1 21:16 sqlitesrc.txt
-rw-rw-r-- 1 deep deep 5.2M Jul 1 21:18 uncompress.txt
没压缩前为5.2M,压缩后为3.2M
数学之路-python计算实战(4)-Lempel-Ziv压缩(2)