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author Jeff Hammel <k0scist@gmail.com>
date Mon, 20 Oct 2025 15:22:19 -0700
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1 #!/usr/bin/env
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2
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3 """
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4 demo related to abstract classes
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5 """
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6
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7 ### roll our own to demo
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8
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9 def abstractmethod(method):
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10 line = method.func_code.co_firstlineno
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11 filename = method.func_code.co_filename
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12 def not_implemented(*args, **kwargs):
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13 raise NotImplementedError('Abstract method %s at File "%s", line %s should be implemented by a concrete class' % (repr(method), filename, line))
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14 return not_implemented
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15
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16 class AbstractBaseClass(object):
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17
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18 @abstractmethod
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19 def foo(self, arg):
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20 """foo does such and such"""
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21
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22 @abstractmethod
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23 def bar(self):
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24 """bar does something else"""
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25
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26 class ConcreteClass(AbstractBaseClass):
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27
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28 def foo(self, arg):
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29 print 'hello'
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30
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31
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32 ### now use the abc module
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33
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34 import abc
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35
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36 class AbstractClass(object):
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37 @abc.abstractmethod
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38 def foo(self, arg):
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39 """blah"""
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40 @abc.abstractmethod
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41 def bar(self):
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42 """bar does nothing"""
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43
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44 class CementClass(AbstractBaseClass):
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45 def foo(self, arg):
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46 print 'goodbye'
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47
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48 class Picasso(object):
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49 __metaclass__ = abc.ABCMeta
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50 @abc.abstractmethod
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51 def foo(self, arg):
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52 """blah"""
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53
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54
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55 if __name__ == '__main__':
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56
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57 # home-rolled
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58 c = ConcreteClass()
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59 c.foo(1)
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60 a = AbstractBaseClass()
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61 try:
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62 a.foo(1)
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63 except NotImplementedError, e:
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64 print e
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65 try:
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66 a.bar()
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67 except NotImplementedError, e:
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68 print e
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69 c.foo(1)
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70 try:
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71 a.foo(1)
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72 except NotImplementedError, e:
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73 print e
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74
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75 ### abc
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76 print '\nIllustrate `abc` functionality'
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77 a = AbstractClass()
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78 e = None
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79 try:
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80 a.foo(1)
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81 # you'd think this would raise an exception since`
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82 # `AbstractClass.foo` is decorated with `abc.abstractmethod`
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83 # But see http://docs.python.org/2/library/abc.html :
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84 # "Using this decorator requires that the class's metaclass
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85 # is ABCMeta or is derived from it."
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86 except Exception, e:
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87 pass
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88 assert e is None # !
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89
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90 # as an aside, another good reason not to use super:
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91 # "Unlike Java abstract methods, these abstract methods may
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92 # have an implementation. This implementation can be called via the super()
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93 # mechanism from the class that overrides it. This could be useful as
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94 # an end-point for a super-call in a framework that uses cooperative
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95 # multiple-inheritance."
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96
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97 a = Picasso()
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98 e = None
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99 try:
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100 a.foo(1)
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101 except Exception, e:
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102 pass
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103 import pdb; pdb.set_trace()