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87
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1 """ Captcha.Base
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2
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3 Base class for all types of CAPTCHA tests. All tests have one or
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4 more solution, determined when the test is generated. Solutions
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5 can be any python object,
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6
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7 All tests can be solved by presenting at least some preset number
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8 of correct solutions. Some tests may only have one solution and require
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9 one solution, but other tests may require N correct solutions of M
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10 possible solutions.
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11 """
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12 #
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13 # PyCAPTCHA Package
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14 # Copyright (C) 2004 Micah Dowty <micah@navi.cx>
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15 #
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16
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17 import random, string, time, shelve
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18
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19 __all__ = ["BaseCaptcha", "Factory", "PersistentFactory"]
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20
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21
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22 def randomIdentifier(alphabet = string.ascii_letters + string.digits,
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23 length = 24):
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24 return "".join([random.choice(alphabet) for i in xrange(length)])
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25
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26
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27 class BaseCaptcha(object):
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28 """Base class for all CAPTCHA tests"""
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29 # Subclasses can override these to set the solution criteria
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30 minCorrectSolutions = 1
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31 maxIncorrectSolutions = 0
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32
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33 def __init__(self):
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34 self.solutions = []
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35 self.valid = True
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36
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37 # Each test has a unique identifier, used to refer to that test
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38 # later, and a creation time so it can expire later.
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39 self.id = randomIdentifier()
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40 self.creationTime = time.time()
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41
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42 def addSolution(self, solution):
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43 self.solutions.append(solution)
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44
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45 def testSolutions(self, solutions):
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46 """Test whether the given solutions are sufficient for this CAPTCHA.
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47 A given CAPTCHA can only be tested once, after that it is invalid
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48 and always returns False. This makes random guessing much less effective.
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49 """
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50 if not self.valid:
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51 return False
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52 self.valid = False
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53
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54 numCorrect = 0
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55 numIncorrect = 0
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56
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57 for solution in solutions:
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58 if solution in self.solutions:
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59 numCorrect += 1
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60 else:
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61 numIncorrect += 1
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62
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63 return numCorrect >= self.minCorrectSolutions and \
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64 numIncorrect <= self.maxIncorrectSolutions
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65
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66
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67 class Factory(object):
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68 """Creates BaseCaptcha instances on demand, and tests solutions.
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69 CAPTCHAs expire after a given amount of time, given in seconds.
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70 The default is 15 minutes.
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71 """
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72 def __init__(self, lifetime=60*15):
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73 self.lifetime = lifetime
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74 self.storedInstances = {}
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75
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76 def new(self, cls, *args, **kwargs):
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77 """Create a new instance of our assigned BaseCaptcha subclass, passing
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78 it any extra arguments we're given. This stores the result for
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79 later testing.
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80 """
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81 self.clean()
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82 inst = cls(*args, **kwargs)
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83 self.storedInstances[inst.id] = inst
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84 return inst
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85
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86 def get(self, id):
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87 """Retrieve the CAPTCHA with the given ID. If it's expired already,
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88 this will return None. A typical web application will need to
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89 new() a CAPTCHA when generating an html page, then get() it later
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90 when its images or sounds must be rendered.
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91 """
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92 return self.storedInstances.get(id)
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93
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94 def clean(self):
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95 """Removed expired tests"""
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96 expiredIds = []
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97 now = time.time()
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98 for inst in self.storedInstances.itervalues():
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99 if inst.creationTime + self.lifetime < now:
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100 expiredIds.append(inst.id)
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101 for id in expiredIds:
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102 del self.storedInstances[id]
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103
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104 def test(self, id, solutions):
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105 """Test the given list of solutions against the BaseCaptcha instance
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106 created earlier with the given id. Returns True if the test passed,
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107 False on failure. In either case, the test is invalidated. Returns
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108 False in the case of an invalid id.
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109 """
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110 self.clean()
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111 inst = self.storedInstances.get(id)
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112 if not inst:
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113 return False
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114 result = inst.testSolutions(solutions)
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115 return result
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116
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117
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118 class PersistentFactory(Factory):
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119 """A simple persistent factory, for use in CGI or multi-process environments
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120 where the state must remain across python interpreter sessions.
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121 This implementation uses the 'shelve' module.
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122 """
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123 def __init__(self, filename, lifetime=60*15):
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124 Factory.__init__(self, lifetime)
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125 self.storedInstances = shelve.open(filename)
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126
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127 ### The End ###
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