Example code - Inheritance issues - Revision history

WikiSysop: /* Take home messages */

2026-03-19T19:22:14Z

Take home messages

← Older revision		Revision as of 21:22, 19 March 2026
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	* Make a copy of mutable class variables if you have any plan or possibility to modify them.		* Make a copy of mutable class variables if you have any plan or possibility to modify them.
	* In magic methods check that the ''other'' class is the same as ''self''.		* In magic methods check that the ''other'' class is the same as ''self''.
			* Notice that what you learned here is slightly different from what was told in the beginning of the powerpoint.

WikiSysop at 18:54, 19 March 2026

2026-03-19T18:54:04Z

← Older revision		Revision as of 20:54, 19 March 2026
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	'feed': "is very excited" }		'feed': "is very excited" }

	### ~~Instatiation~~		### Instantiation
	def __init__(self, name, gender):		def __init__(self, name, gender):
	self._name, self._gender = name, gender		self._name, self._gender = name, gender
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	'feed': "is very excited" }		'feed': "is very excited" }

	### ~~Instatiation~~		### Instantiation
	def __init__(self, name, gender):		def __init__(self, name, gender):
	self._name, self._gender = name, gender		self._name, self._gender = name, gender

WikiSysop: /* Take home messages */

2026-03-19T18:52:06Z

Take home messages

← Older revision		Revision as of 20:52, 19 March 2026
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	== Take home messages ==		== Take home messages ==
	* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.		* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.
	* Don't hardcode class names in your class. Use ''type(self)'' to get the class. This goes when using class variables, constructing new instances.		* Don't hardcode class names in your class. Use ''type(self)'' to get the class. This goes when using class variables, constructing new instances and elsewhere. But not when copying the parent class' class variables - there you have to name it :-)
	* Make a copy of mutable class variables if you have any plan or possibility to modify them.		* Make a copy of mutable class variables if you have any plan or possibility to modify them.
	* In magic methods check that the ''other'' class is the same as ''self''.		* In magic methods check that the ''other'' class is the same as ''self''.

WikiSysop: /* Take home messages */

2026-03-19T18:48:00Z

Take home messages

← Older revision		Revision as of 20:48, 19 March 2026
Line 253:		Line 253:
	== Take home messages ==		== Take home messages ==
	* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.		* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.
	* Don't hardcode class names in your class. Use ''type(self)'' to get the class.		* Don't hardcode class names in your class. Use ''type(self)'' to get the class. This goes when using class variables, constructing new instances.
	* Make a copy of mutable class variables if you have any plan or possibility to modify them.		* Make a copy of mutable class variables if you have any plan or possibility to modify them.
			* In magic methods check that the ''other'' class is the same as ''self''.

WikiSysop: /* Take home messages */

2026-03-19T18:44:30Z

Take home messages

← Older revision		Revision as of 20:44, 19 March 2026
Line 254:		Line 254:
	* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.		* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.
	* Don't hardcode class names in your class. Use ''type(self)'' to get the class.		* Don't hardcode class names in your class. Use ''type(self)'' to get the class.
			* Make a copy of mutable class variables if you have any plan or possibility to modify them.

WikiSysop at 18:42, 19 March 2026

2026-03-19T18:42:29Z

← Older revision		Revision as of 20:42, 19 March 2026
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	acts['feed'] = 'demands more meat'		acts['feed'] = 'demands more meat'
	</pre>		</pre>
	== Take home messages		== Take home messages ==
	* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.		* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.
	* Don't hardcode class names in your class. Use ''type(self)'' to get the class.		* Don't hardcode class names in your class. Use ''type(self)'' to get the class.

WikiSysop at 18:42, 19 March 2026

2026-03-19T18:42:10Z

← Older revision		Revision as of 20:42, 19 March 2026
Line 160:		Line 160:
	</pre>		</pre>
	That was unfortunate. We should not be able to breed a cat and a tiger, and if we did anyway, should the result be a cat (the kitten does a cat action)?<br>		That was unfortunate. We should not be able to breed a cat and a tiger, and if we did anyway, should the result be a cat (the kitten does a cat action)?<br>
	The issue is in the ''__add__'' magic method. All ~~the~~ is required is that the two classes being "added" have a _gender instance variable.		The issue is in the ''__add__'' magic method. All that is required is that the two classes being "added" have a _gender instance variable.
	<pre>		<pre>
	def __add__(self, other):		def __add__(self, other):
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	acts['feed'] = 'demands more meat'		acts['feed'] = 'demands more meat'
	</pre>		</pre>
			== Take home messages
			* Even if you do not plan for your class to be inherited, make it so it can. That way it is less work later AND you remember how to do it.
			* Don't hardcode class names in your class. Use ''type(self)'' to get the class.

WikiSysop at 18:36, 19 March 2026

2026-03-19T18:36:46Z

@@ Line 180: / Line 180: @@
          kitten = type(self)('Unnamed kitten', 'male')
          return kitten
 </pre>

WikiSysop at 18:19, 19 March 2026

2026-03-19T18:19:06Z

← Older revision		Revision as of 20:19, 19 March 2026
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	# Adding a class check - we must demand that we breed tigers with tigers and cats with cats		# Adding a class check - we must demand that we breed tigers with tigers and cats with cats
	def __add__(self, other):		def __add__(self, other):
	if type(self~~._gender =~~= other~~._gender~~:		if type(self) != type(other):
	return NotImplemented		return NotImplemented
	# Taken a short cut and just demanding the genders to be different to breed		# Taken a short cut and just demanding the genders to be different to breed
	if self._gender == other._gender:		if self._gender == other._gender:
	return NotImplemented		return NotImplemented
	# ~~Being biased~~ and ~~saying all kittens are male~~		# Still male kittens, making sure tigers begets tigers and cats begets cats
	kitten = ~~CatClass~~('Unnamed kitten', 'male')		kitten = type(self)('Unnamed kitten', 'male')
	return kitten		return kitten

	</pre>		</pre>

WikiSysop at 17:48, 19 March 2026

2026-03-19T17:48:08Z

← Older revision		Revision as of 19:48, 19 March 2026
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	kitten1 = mycat + yourcat		kitten1 = mycat + yourcat
	print(kitten1.name)		print(kitten1.name)

			# Can we mate the cat and the tiger?
			kitten2 = yourcat + tigger
			kitten2.name = "Monstrous Mutant"
			print(kitten2.name)
			kitten2.action('scratch')
			</pre>
			That was unfortunate. We should not be able to breed a cat and a tiger, and if we did anyway, should the result be a cat (the kitten does a cat action)?<br>
			The issue is in the ''__add__'' magic method. All the is required is that the two classes being "added" have a _gender instance variable.
			<pre>
			def __add__(self, other):
			# Taken a short cut and just demanding the genders to be different to breed
			if self._gender == other._gender:
			return NotImplemented
			# Being biased and saying all kittens are male
			kitten = CatClass('Unnamed kitten', 'male')
			return kitten

			# Adding a class check - we must demand that we breed tigers with tigers and cats with cats
			def __add__(self, other):
			if type(self._gender == other._gender:
			return NotImplemented
			# Taken a short cut and just demanding the genders to be different to breed
			if self._gender == other._gender:
			return NotImplemented
			# Being biased and saying all kittens are male
			kitten = CatClass('Unnamed kitten', 'male')
			return kitten

			</pre>