How to extend a class in python

Question

In python how can you extend a class  For example if I have  color py  class Color      def   init   self  color           self color   color     def getcolor self           return self color   color extended py  import Color  class Color      def getcolor self           return self color     extended     But this doesn t work    I expect that if I work in color extended py  then when I make a color object and use the getcolor function then it will return the object with the string   extended   in the end  Also it should have gotton the init from the import   Assume python 3 1  Thanks

User · Accepted Answer

Use   import color  class Color color Color             If this were Python 2 x  you would also want to derive color Color from object  to make it a new-style class   class Color object             This is not necessary in Python 3 x

User · Answer

Another way to extend  specifically meaning  add new methods  not change existing ones  classes  even built-in ones  is to use a preprocessor that adds the ability to extend out of above the scope of Python itself  converting the extension to normal Python syntax before Python actually gets to see it   I ve done this to extend Python 2 s str   class  for instance  str   is a particularly interesting target because of the implicit linkage to quoted data such as  this  and  that    Here s some extending code  where the only added non-Python syntax is the extend testDottedQuad bit   extend testDottedQuad def testDottedQuad strObject       if not isinstance strObject  basestring   return False     listStrings   strObject split          if len listStrings     4  return False     for strNum in listStrings          try     val   int strNum          except  return False         if val  lt  0  return False         if val  gt  255  return False     return True   After which I can write in the code fed to the preprocessor   if  192 168 1 100  testDottedQuad        doSomething    dq    216 126 621 5  if not dq testDottedQuad        throwWarning     dqt      join   127       0       0       1    testDottedQuad   if dqt      print  well  that was fun    The preprocessor eats that  spits out normal Python without monkeypatching  and Python does what I intended it to do   Just as a c preprocessor adds functionality to c  so too can a Python preprocessor add functionality to Python   My preprocessor implementation is too large for a stack overflow answer  but for those who might be interested  it is here on GitHub

User · Answer

class MyParent       def sayHi            print  Mamma says hi    from path to MyParent import MyParent  class ChildClass MyParent       pass  An instance of ChildClass will then inherit the sayHi   method

[python] How to extend a class in python?

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