overload __add__

[TMS]

OK, I'm building this reactor software (an assignment) that takes particles and shows a chain reaction.

Here is the code I have so far:

class Particle:
	def __init__(self, symbol, charge, number):
		self.symbol = symbol
		self.charge = charge
		self.number = number
	def __repr__(self):
		return self.symbol
class Nucleus(Particle):
	def __repr__(self):
		return "(%d)%s" % (self.number, self.symbol)
class UnbalancedCharge:
	pass #worry about this later
class UnbalancedNumber:
	pass #worry about this later
 
class Reaction: # this is the class I'm having trouble with
	def __init__(symbol, charge, number):
		lhs = number, symbol
		rhs = number, symbol
		print lhs # just a test
	#def __repr__(lhs, rhs): //this is what I'll return later, when I get lhs and rhs to access correct information
		#return lhs, rhs
 
if __name__ == '__main__':
	em = Particle("e-", -1, 0)
	ep = Particle("e+", 1, 0)
	p = Particle("p", 1, 1)
	n = Particle("n", 0, 1)
	neutrino = Particle("nu_e", 0, 0)
	gamma = Particle("gamma", 0, 0)			 
	print em, ep, p, n, neutrino, gamma
	d = Nucleus("H", 1, 2)
	li6 = Nucleus("li", 3, 6)
	he4 = Nucleus("He", 2, 4)
	print d
	print li6
	print he4
	print Reaction((li6, d), (he4, he4))

The problem is in the Reaction class. It should print out like this:

(6)Li + (2)H -> (4)He + (4)He

Right now its only giving me the following:

e- e+ p n nu_e gamma
(2)H
(6)li
(4)He
(((4)He, (4)He), <__main__.React ion instance at 0x00C42670>) (((4)He, (4)He), <__main__.React ion instance at 0x00C42670>)
<__main__.React ion instance at 0x00C42670>
>>>

The final one starting with (((4)He, (4)He), is the part I don't want and should look like the example I gave.

So, I think I'm going the right direction but its printing the second particles twice, and not using the first particles at all. Plus its giving me the address in memory, and I most definitely don't want that. At first I thought it was inheritance, but I can see now that it isn't. The Nucleus prints the correct format for one particle, so I need to reuse that to make this class print out what I need. Can someone give me a nudge in the right direction, please?

Thanks

[bvdet]

You are mismatching your arguments:

class Reaction:
	def __init__(self, lhs, rhs):
		self.lhs = lhs
		self.rhs = rhs

Now self.lhs and self.rhs are tuples. To print the elements:

self.lhs[0], self.lhs[1], self.rhs[0], self.rhs[1]

[TMS]

I'm getting an error message with that. Here is what I did (I had already figured out the self.lhs = lhs and I got it to print... but not right).

class Reaction:
	def __init__(self, lhs, rhs):
		self.lhs = lhs
		self.rhs = rhs
	def __repr__ (self): 
		return self.lhs[0], "+", self.lhs[1], "->", self.rhs[0], "+", self.rhs[1]

Here is the error:
Traceback (most recent call last):
File "C:\Python25\pa rt.py", line 44, in <module>
print Reaction((li6, d), (he4, he4))
TypeError: __str__ returned non-string (type tuple)

But when I print from __init__ I get this:

((6)li, (2)h) ((4)he, (4)he)

So, I am accessing it, its returning a tuple and I don't know how to fix it.

:(

[ghostdog74]

I'm getting an error message with that. Here is what I did (I had already figured out the self.lhs = lhs and I got it to print... but not right).

class Reaction:
	def __init__(self, lhs, rhs):
		self.lhs = lhs
		self.rhs = rhs
	def __repr__ (self): 
		return self.lhs[0], "+", self.lhs[1], "->", self.rhs[0], "+", self.rhs[1]

Here is the error:
Traceback (most recent call last):
File "C:\Python25\pa rt.py", line 44, in <module>
print Reaction((li6, d), (he4, he4))
TypeError: __str__ returned non-string (type tuple)

But when I print from __init__ I get this:

((6)li, (2)h) ((4)he, (4)he)

So, I am accessing it, its returning a tuple and I don't know how to fix it.

:(

how about this

....
def __repr__ (self): 	
	s = "%s+%s->%s+%s" %(self.lhs[0],self.lhs[1],self.rhs[0],self.rhs[1])
	return s

[TMS]

ah... thank you

[TMS]

ok, new problem on this assignment.

For me, this is rather complicated, so I will try to make it as simple as possible. I've gotten the reactor to take in an element, then add 2 elements 2 different ways. Now I need to get it to add 3 different elements. (not really add, just look as if it is adding). Here is my code:

"""
Assignment: Homework #6
Create a class called Reaction, will have a left hand side and right hand side, specified by tuples
containing one or more particles (including Nucleuses). The reaction taking place transofrms
the particles on the left-hand side to the particles on the right hand side.
"""
class Particle:
	def __init__(self, symbol, charge, number):
		self.symbol = symbol
		self.charge = charge
		self.number = number
 
	def __add__(left, right):
		"""
		#2. Extend the Particle class to have the "+" operator acting on two particles
		result in a tuple containing them, so that print Reaction(li6+d, he4 + he4) is
		equivalent to print Reaction((li6, d), (he4, he4)), this uses class Reaction to print out
		the correct format.
		"""
		return left, right
	def __repr__(self):
		return self.symbol
 
class Nucleus(Particle):
	def __repr__(self):
		return "(%d)%s" % (self.number, self.symbol)
class UnbalancedCharge:
	pass #worry about this later
class UnbalancedNumber:
	pass #worry about this later
class Reaction:
	def __init__(self, lhs, rhs):
		"""
		Initialize the left hand side and right hand side so that print Reaction(li6, d)(he4, he4)
		will produce (6)LI + (2)H -> (4)He + (4)He
		"""
		self.lhs = lhs
		self.rhs = rhs
	def __repr__ (self):
		s = "%s+%s->%s+%s" % (self.lhs[0], self.lhs[1], self.rhs[0], self.rhs[1])
		return s
class chainReaction(Reaction):
	def __init__(self, name):
		self.name = name
	def chain(self, lhsNet, rhsNet):
		pass #combine
	def __repr__ (self):
		return "%s %s" % (self.name, "chain:" )
 
if __name__ == '__main__':
	em = Particle("e-", -1, 0)
	ep = Particle("e+", 1, 0)
	p = Particle("p", 1, 1)
	n = Particle("n", 0, 1)
	neutrino = Particle("nu_e", 0, 0)
	gamma = Particle("gamma", 0, 0)			 
	print em, ep, p, n, neutrino, gamma
	d = Nucleus("h", 1, 2)
	li6 = Nucleus("li", 3, 6)
	he4 = Nucleus("he", 2, 4)
	print d
	print li6
	print he4
	print Reaction((li6, d), (he4, he4))
	print Reaction(li6 + d, he4 + he4)
	he3 = Nucleus("he", 2, 3)
	chnPP = chainReaction("proton-proton (branch I)")
	print chnPP
	print Reaction(li6 + d + he4) #this one gives me trouble

The last print request is the one I can't seem to figure out. I've tried re-writing the function that is called when I add 2 by adding middle, but it doesn't work. I mean, like this:

 
def __addMore__(left, right, middle):
	return left, right, middle

because it works so well for the one that 'adds' two, but it doesn't work. I need this because eventually I have to write a net reaction that combines reactions on the left side, then 'points' to the reactions on the right hand side. One of the reactions for the sun looks like this:

Reaction(p + p, d + ep + neutrino, chnPP)

which has a part with 2 elements, then 3, then the name of the reaction which I defined in a different class. I will do that later, for now I simply need to get the program to add three as the test shows on my code.

Any ideas?

[bartonc]

ok, new problem on this assignment.

For me, this is rather complicated, so I will try to make it as simple as possible. I've gotten the reactor to take in an element, then add 2 elements 2 different ways. Now I need to get it to add 3 different elements. (not really add, just look as if it is adding). Here is my code:

"""
Assignment: Homework #6
Create a class called Reaction, will have a left hand side and right hand side, specified by tuples
containing one or more particles (including Nucleuses). The reaction taking place transofrms
the particles on the left-hand side to the particles on the right hand side.
"""
class Particle:
	def __init__(self, symbol, charge, number):
		self.symbol = symbol
		self.charge = charge
		self.number = number
 
	def __add__(left, right):
		"""
		#2. Extend the Particle class to have the "+" operator acting on two particles
		result in a tuple containing them, so that print Reaction(li6+d, he4 + he4) is
		equivalent to print Reaction((li6, d), (he4, he4)), this uses class Reaction to print out
		the correct format.
		"""
		return left, right
	def __repr__(self):
		return self.symbol
 
class Nucleus(Particle):
	def __repr__(self):
		return "(%d)%s" % (self.number, self.symbol)
class UnbalancedCharge:
	pass #worry about this later
class UnbalancedNumber:
	pass #worry about this later
class Reaction:
	def __init__(self, lhs, rhs):
		"""
		Initialize the left hand side and right hand side so that print Reaction(li6, d)(he4, he4)
		will produce (6)LI + (2)H -> (4)He + (4)He
		"""
		self.lhs = lhs
		self.rhs = rhs
	def __repr__ (self):
		s = "%s+%s->%s+%s" % (self.lhs[0], self.lhs[1], self.rhs[0], self.rhs[1])
		return s
class chainReaction(Reaction):
	def __init__(self, name):
		self.name = name
	def chain(self, lhsNet, rhsNet):
		pass #combine
	def __repr__ (self):
		return "%s %s" % (self.name, "chain:" )
 
if __name__ == '__main__':
	em = Particle("e-", -1, 0)
	ep = Particle("e+", 1, 0)
	p = Particle("p", 1, 1)
	n = Particle("n", 0, 1)
	neutrino = Particle("nu_e", 0, 0)
	gamma = Particle("gamma", 0, 0)			 
	print em, ep, p, n, neutrino, gamma
	d = Nucleus("h", 1, 2)
	li6 = Nucleus("li", 3, 6)
	he4 = Nucleus("he", 2, 4)
	print d
	print li6
	print he4
	print Reaction((li6, d), (he4, he4))
	print Reaction(li6 + d, he4 + he4)
	he3 = Nucleus("he", 2, 3)
	chnPP = chainReaction("proton-proton (branch I)")
	print chnPP
	print Reaction(li6 + d + he4) #this one gives me trouble

The last print request is the one I can't seem to figure out. I've tried re-writing the function that is called when I add 2 by adding middle, but it doesn't work. I mean, like this:

 
def __addMore__(left, right, middle):
	return left, right, middle

because it works so well for the one that 'adds' two, but it doesn't work. I need this because eventually I have to write a net reaction that combines reactions on the left side, then 'points' to the reactions on the right hand side. One of the reactions for the sun looks like this:

Reaction(p + p, d + ep + neutrino, chnPP)

which has a part with 2 elements, then 3, then the name of the reaction which I defined in a different class. I will do that later, for now I simply need to get the program to add three as the test shows on my code.

Any ideas?

__add__() and all others with those names are internal to python and are called operator overloads (they let your code resond to operators ("+" in this case)). You don't get to addMore of them to the language. If your __add__() is working correctly, python will do the work: first evaluate d+ep, then add neutrino to the result.

[TMS]

so maybe adding an if statement to the __add__ function? Because sometimes it takes two elements and sometimes 3. If so, I'll have to think for a bit how to logically make that work.

tms

[bvdet]

so maybe adding an if statement to the __add__ function? Because sometimes it takes two elements and sometimes 3. If so, I'll have to think for a bit how to logically make that work.

tms

Yep!

	def __add__(self, p2):
		"""
		#2. Extend the Particle class to have the "+" operator acting on two particles
		result in a tuple containing them, so that print Reaction(li6+d, he4 + he4) is
		equivalent to print Reaction((li6, d), (he4, he4)), this uses class Reaction to print out
		the correct format.
		"""
		if isinstance(p2, tuple):
			return (self,) + p2
		else:
			return self, p2

You will need to use parentheses such that you are adding two instances or one instance and one tuple.

	print li6+d
	print li6+(d+he4)
	print he4+(he4+(he4+(he4+(he4+he4))))
# Yields:
>>> ((6)Li, (2)H)
((6)Li, (2)H, (4)He)
((4)He, (4)He, (4)He, (4)He, (4)He, (4)He)
>>>

Not ideal but seems to work.

[bvdet]

so maybe adding an if statement to the __add__ function? Because sometimes it takes two elements and sometimes 3. If so, I'll have to think for a bit how to logically make that work.

tms

Now you need to get a Reaction() instance to display properly. It only expects two elements on each side, so you need to build the return string allowing for the variable length of tuples on each side. Insead of me posting code, I think you can do it.

[TMS]

:)

I was also toying with __radd__ but couldn't really get that to work. I think I can figure it out from here. Thank you!

[bartonc]

Ok guys, it's time for me to rename this thread. Either of you have a preference?

[TMS]

yes, I was thinking it would be appropriate to rename it also. How about

overload __add__

or something similar?

[bartonc]

yes, I was thinking it would be appropriate to rename it also. How about

overload __add__

or something similar?

You got it! Thanks.