ais.aisstring

Source Code for Module ais.aisstring

1 #!/usr/bin/env python 2 3 __version__ = '$Revision: 2068 $'.split()[1] 4 __date__ = '$Date: 2006-05-02 08:17:59 -0400 (Tue, 02 May 2006) $'.split()[1] 5 __author__ = 'Kurt Schwehr' 6 7 __doc__=''' 8 Handle encoding and decoding AIS strings. 9 10 @bug: need some more interesting doctests! 11 @bug: needs to throw an exception if the character is not in the LUT 12 @bug: what to do about string with trailing @@@ or " " (white space) 13 14 @var characterLUT: lookup table for decode to fetch characters faster 15 @type characterLUT: list 16 17 @var characterBits: lookup table for going from a single character to a 6 bit BitVector 18 @type characterBits: dict 19 20 21 @author: '''+__author__+''' 22 @version: ''' + __version__ +''' 23 @copyright: 2006 24 25 @var __date__: Date of last svn commit 26 @undocumented: __version__ __author__ __doc__ myparser 27 @undocumented: buildDict 28 ''' 29 30 31 32 # python standard library 33 import sys 34 35 # External libs 36 from BitVector import BitVector 37 38 # Local 39 import binary 40 #import verbosity 41 #from verbosity import BOMBASTIC,VERBOSE,TRACE,TERSE,ALWAYS 42 43 characterLUT=[ '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 44 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 45 'Z', '[', '\\', ']', '^', '-', ' ', 46 '!', '"', '#', '$', '%', '&', '`', '(', ')', '*', '+', ',', '-', '.', '/', 47 '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 48 ':', ';', '<', '=', '>', '?' 49 ] 50 51 characterDict={ 52 '@': 0, 'A': 1, 'B': 2, 'C': 3, 'D': 4, 'E': 5, 'F': 6, 53 'G': 7, 'H': 8, 'I': 9, 'J': 10, 'K': 11, 'L': 12, 'M': 13, 54 'N': 14, 'O': 15, 'P': 16, 'Q': 17, 'R': 18, 'S': 19, 'T': 20, 55 'U': 21, 'V': 22, 'W': 23, 'X': 24, 'Y': 25, 'Z': 26, '[': 27, 56 '\\': 28, ']': 29, '^': 30, '-': 31, ' ': 32, '!': 33, '"': 34, 57 '#': 35, '$': 36, '%': 37, '&': 38, '`': 39, '(': 40, ')': 41, 58 '*': 42, '+': 43, ',': 44, '-': 45, '.': 46, '/': 47, '0': 48, 59 '1': 49, '2': 50, '3': 51, '4': 52, '5': 53, '6': 54, '7': 55, 60 '8': 56, '9': 57, ':': 58, ';': 59, '<': 60, '=': 61, '>': 62, 61 '?': 63 62 } 63 '''Fast lookup for the AIS int code for a character ''' 64 # The above illustrates the inline ways of documenting module variables 65 66 67 characterBits={} 68 characterBits['@']=binary.setBitVectorSize(BitVector(intVal=0),6) 69 characterBits['A']=binary.setBitVectorSize(BitVector(intVal=1),6) 70 characterBits['B']=binary.setBitVectorSize(BitVector(intVal=2),6) 71 characterBits['C']=binary.setBitVectorSize(BitVector(intVal=3),6) 72 characterBits['D']=binary.setBitVectorSize(BitVector(intVal=4),6) 73 characterBits['E']=binary.setBitVectorSize(BitVector(intVal=5),6) 74 characterBits['F']=binary.setBitVectorSize(BitVector(intVal=6),6) 75 characterBits['G']=binary.setBitVectorSize(BitVector(intVal=7),6) 76 characterBits['H']=binary.setBitVectorSize(BitVector(intVal=8),6) 77 characterBits['I']=binary.setBitVectorSize(BitVector(intVal=9),6) 78 characterBits['J']=binary.setBitVectorSize(BitVector(intVal=10),6) 79 characterBits['K']=binary.setBitVectorSize(BitVector(intVal=11),6) 80 characterBits['L']=binary.setBitVectorSize(BitVector(intVal=12),6) 81 characterBits['M']=binary.setBitVectorSize(BitVector(intVal=13),6) 82 characterBits['N']=binary.setBitVectorSize(BitVector(intVal=14),6) 83 characterBits['O']=binary.setBitVectorSize(BitVector(intVal=15),6) 84 characterBits['P']=binary.setBitVectorSize(BitVector(intVal=16),6) 85 characterBits['Q']=binary.setBitVectorSize(BitVector(intVal=17),6) 86 characterBits['R']=binary.setBitVectorSize(BitVector(intVal=18),6) 87 characterBits['S']=binary.setBitVectorSize(BitVector(intVal=19),6) 88 characterBits['T']=binary.setBitVectorSize(BitVector(intVal=20),6) 89 characterBits['U']=binary.setBitVectorSize(BitVector(intVal=21),6) 90 characterBits['V']=binary.setBitVectorSize(BitVector(intVal=22),6) 91 characterBits['W']=binary.setBitVectorSize(BitVector(intVal=23),6) 92 characterBits['X']=binary.setBitVectorSize(BitVector(intVal=24),6) 93 characterBits['Y']=binary.setBitVectorSize(BitVector(intVal=25),6) 94 characterBits['Z']=binary.setBitVectorSize(BitVector(intVal=26),6) 95 characterBits['[']=binary.setBitVectorSize(BitVector(intVal=27),6) 96 characterBits['\\']=binary.setBitVectorSize(BitVector(intVal=28),6) 97 characterBits[']']=binary.setBitVectorSize(BitVector(intVal=29),6) 98 characterBits['^']=binary.setBitVectorSize(BitVector(intVal=30),6) 99 characterBits['-']=binary.setBitVectorSize(BitVector(intVal=31),6) 100 characterBits[' ']=binary.setBitVectorSize(BitVector(intVal=32),6) 101 characterBits['!']=binary.setBitVectorSize(BitVector(intVal=33),6) 102 characterBits['"']=binary.setBitVectorSize(BitVector(intVal=34),6) 103 characterBits['#']=binary.setBitVectorSize(BitVector(intVal=35),6) 104 characterBits['$']=binary.setBitVectorSize(BitVector(intVal=36),6) 105 characterBits['%']=binary.setBitVectorSize(BitVector(intVal=37),6) 106 characterBits['&']=binary.setBitVectorSize(BitVector(intVal=38),6) 107 characterBits['`']=binary.setBitVectorSize(BitVector(intVal=39),6) 108 characterBits['(']=binary.setBitVectorSize(BitVector(intVal=40),6) 109 characterBits[')']=binary.setBitVectorSize(BitVector(intVal=41),6) 110 characterBits['*']=binary.setBitVectorSize(BitVector(intVal=42),6) 111 characterBits['+']=binary.setBitVectorSize(BitVector(intVal=43),6) 112 characterBits[',']=binary.setBitVectorSize(BitVector(intVal=44),6) 113 characterBits['-']=binary.setBitVectorSize(BitVector(intVal=45),6) 114 characterBits['.']=binary.setBitVectorSize(BitVector(intVal=46),6) 115 characterBits['/']=binary.setBitVectorSize(BitVector(intVal=47),6) 116 characterBits['0']=binary.setBitVectorSize(BitVector(intVal=48),6) 117 characterBits['1']=binary.setBitVectorSize(BitVector(intVal=49),6) 118 characterBits['2']=binary.setBitVectorSize(BitVector(intVal=50),6) 119 characterBits['3']=binary.setBitVectorSize(BitVector(intVal=51),6) 120 characterBits['4']=binary.setBitVectorSize(BitVector(intVal=52),6) 121 characterBits['5']=binary.setBitVectorSize(BitVector(intVal=53),6) 122 characterBits['6']=binary.setBitVectorSize(BitVector(intVal=54),6) 123 characterBits['7']=binary.setBitVectorSize(BitVector(intVal=55),6) 124 characterBits['8']=binary.setBitVectorSize(BitVector(intVal=56),6) 125 characterBits['9']=binary.setBitVectorSize(BitVector(intVal=57),6) 126 characterBits[':']=binary.setBitVectorSize(BitVector(intVal=58),6) 127 characterBits[';']=binary.setBitVectorSize(BitVector(intVal=59),6) 128 characterBits['<']=binary.setBitVectorSize(BitVector(intVal=60),6) 129 characterBits['=']=binary.setBitVectorSize(BitVector(intVal=61),6) 130 characterBits['>']=binary.setBitVectorSize(BitVector(intVal=62),6) 131 characterBits['?']=binary.setBitVectorSize(BitVector(intVal=63),6) 132 133

134 -def buildDict():

135 ''' 136 Helper to build the build the carachterBits and Dict tables 137 138 @rtype: test to stdout 139 ''' 140 count=0 141 print 'characterDict={' 142 for i in range(len(characterLUT)): 143 count += 1 144 c = characterLUT[i] 145 if c=='\\': c='\\\\' 146 print "'"+c+"': "+str(i)+",", 147 if count%6==0: 148 print 149 print '}' 150 151 print 'characterBits={}' 152 for i in range(len(characterLUT)): 153 c = characterLUT[i] 154 if c=='\\': c='\\\\' 155 print "characterBits['"+c+"']"+'=binary.setBitVectorSize(BitVector(intVal='+str(i)+'),6)'

156 157

158 -def decode(bits,dropAfterFirstAt=False):

159 ''' 160 Decode bits as a string. Does not remove the end space or @@@@. Must be an multiple of 6 bits. 161 162 @param bits: n*6 bits that represent a string. 163 @type bits: BitVector 164 @return: string with pad spaces or @@@@ 165 @rtype: str 166 ''' 167 #assert(len(bits) % 6 == 0) 168 numchar=len(bits)/6 169 s = [] 170 for i in range(numchar): # FIX: off by one? 171 start = 6 * i 172 end = start+6 #6 * (i+1) 173 charbits=bits[start:end] 174 val = int(charbits) 175 if dropAfterFirstAt and val==0: 176 break # 0 is the @ character which is used to pad strings. 177 s.append(characterLUT[val]) 178 179 return ''.join(s)

180 181

182 -def encode(string,bitSize=None):

183 ''' 184 @param string: python ascii string to encode. 185 @type string: str 186 @param bitSize: how many bits should this take. must be a multiple of 6 187 @type bitSize: int 188 @return: enocded bits for the string 189 @rtype: BitVector 190 @bug: force to upper case 191 @bug: building this in reverse may be faster 192 @bug: check that bitSize is a multple of 6 193 @bug: pad with "@" to reach requested bitSize 194 ''' 195 if bitSize: 196 assert(bitSize%6==0) 197 bv = BitVector(size=0) 198 for i in range(len(string)): 199 bv = bv+characterBits[string[i]] 200 if bitSize: 201 if bitSize < len(bv): 202 print 'ERROR: string longer than specified bit count: "'+string+'"', bitSize, len(bv) 203 assert False 204 extra = bitSize - len(bv) 205 bv = bv+BitVector(size=extra) 206 return bv

207

208 -def unpad(string,removeBlanks=True):

209 """ 210 Remove AIS string padding 211 212 >>> unpad('@') 213 '' 214 >>> unpad('A@') 215 'A' 216 >>> unpad('ABCDEF1234@@@@@') 217 'ABCDEF1234' 218 219 FIX: is this the correct response? 220 221 >>> unpad('A@B') 222 'A@B' 223 224 This is non standard behavior, but some AIS systems space pad the right 225 226 >>> unpad(' ') 227 '' 228 >>> unpad('MY SHIP NAME ') 229 'MY SHIP NAME' 230 231 The standard implies this behavior with is less fun 232 233 >>> unpad('MY SHIP NAME ',removeBlanks=False) 234 'MY SHIP NAME ' 235 236 @bug: use a faster algorithm for truncating the string 237 @param string: string to cleanup 238 @type string: str 239 @param removeBlanks: set to true to strip spaces on the right 240 @type removeBlanks: bool 241 @return: cleaned up string 242 @rtype: str 243 """ 244 while len(string)>0 and string[-1]=='@': 245 string=string[:-1] 246 if removeBlanks: 247 while len(string)>0 and string[-1]==' ': 248 string=string[:-1] 249 return string

250

251 -def pad(string,length):

252 ''' 253 pad a string out to the proper length with the @ character as required by the ais spec 254 255 >>> pad('',0) 256 '' 257 >>> pad('',1) 258 '@' 259 >>> pad('A',1) 260 'A' 261 >>> pad('A',2) 262 'A@' 263 >>> pad('MY SHIP NAME',20) 264 'MY SHIP NAME@@@@@@@@' 265 266 @param string: string to pad out 267 @type string: str 268 @param length: number of characters that the string must be 269 @type length: int 270 @return: str of len length 271 @rtype: str 272 273 @bug: Use a list and join to make the string building faster 274 ''' 275 while len(string)<length: string += '@' 276 return string

277 278 279 if __name__ == '__main__': 280 from optparse import OptionParser 281 myparser = OptionParser(usage="%prog [options]",version="%prog "+__version__) 282 myparser.add_option('--test','--doc-test',dest='doctest',default=False,action='store_true', 283 help='run the documentation tests') 284 # verbosity.addVerbosityOptions(myparser) 285 (options,args) = myparser.parse_args() 286 287 success=True 288 289 if options.doctest: 290 import os; print os.path.basename(sys.argv[0]), 'doctests ...', 291 sys.argv= [sys.argv[0]] 292 # if options.verbosity>=VERBOSE: sys.argv.append('-v') 293 import doctest 294 numfail,numtests=doctest.testmod() 295 if numfail==0: print 'ok' 296 else: 297 print 'FAILED' 298 success=False 299 300 if not success: 301 sys.exit('Something Failed') 302