help with addition of dictionary values

[cLoque]

hi,

i would like to add my two matrices, using __add__

class m:

    def __init__(self, mtx={}, m=0, n=0):
        self.matrix = {}
        self.matrix.update(mtx)
        self.row = m
        self.col = n

    def __getitem__(self, ij):
        return self.matrix.get(ij,0)

    def __setitem__(self, ij, val):
        self.matrix[i,j] = val

    def __add__(self, other):
        result = m()
        for i in other:
            self.result[i] = self.matrix.get(i, 0) + other[i]
        return result

but i always get an error.

Hope you can help me

[bartonc]

Use the dictionary method, items(). Like this:[CODE=python]
>>> dd_1 = {'a':1, 'b':2, 'c':3}
>>> dd_2 = {'a':3, 'b':4}
>>> dd_res = {}
>>> for key, value in dd_1.items():
... dd_res[key] = dd_2.get(key, 0) + value
...
>>> dd_res
{'a': 4, 'c': 3, 'b': 6}
>>> [/CODE]

[cLoque]

Use the dictionary method, items. Like this:[CODE=python]
>>> dd_1 = {'a':1, 'b':2, 'c':3}
>>> dd_2 = {'a':3, 'b':4}
>>> dd_res = {}
>>> for key, value in dd_1.items():
... dd_res[key] = dd_2.get(key, 0) + value
...
>>> dd_res
{'a': 4, 'c': 3, 'b': 6}
>>> [/CODE]

for this loop what does value means here? how can i use the one that i have set in __setitem__? does get(key, 0) gives me the value that i have set in __setitem__?

sorry if i sound confusing, but honestly i'm confused with the passing of tuples, i want to know exactly where does each value goes after using the method. am already fine with __init__ method, i'm just confused what happens to the values after setting them

for key, value in dd_1.items():
... dd_res[key] = dd_2.get(key, 0) + value

[bartonc]

for this loop what does value means here? how can i use the one that i have set in __setitem__? does get(key, 0) gives me the value that i have set in __setitem__?

sorry if i sound confusing, but honestly i'm confused with the passing of tuples, i want to know exactly where does each value goes after using the method. am already fine with __init__ method, i'm just confused what happens to the values after setting them

for key, value in dd_1.items():
... dd_res[key] = dd_2.get(key, 0) + value

OK. Your class is coming along nicely. The on-line help can probably explain these things better that I can (more succinctly, anyway):[CODE=python]
>>> help(dd_1.get)
Help on built-in function get:

get(...)
D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None.

>>> help(dd_1.items )
Help on built-in function items:

items(...)
D.items() -> list of D's (key, value) pairs, as 2-tuples[/CODE]But probably the best way to learn what a chunk of code (your own or someone else's) is like this:[CODE=python]
>>> for key, value in dd_1.items():
... print key, value
... dd_res[key] = dd_2.get(key, 0) + value[/CODE]

[bartonc]

If the assignment doesn't allow using a subclass, you'll have to use the tricks below to take this apart and create your own class:[CODE=python]
...
>>> class sm(dict):
... def __add__(self, other):
... res = sm()
... for key, value in other.items():
... mine = self.get(key, 0)
... res[key] = mine + value
... return res
...
>>> sm_1 = sm({(0,0):5, (0,1):2})
>>> sm_2 = sm({(0,0):7, (0,1):1})
>>> sm_1 + sm_2
{(0, 1): 3, (0, 0): 12}
>>> [/CODE]You'll also need to add some additional logic to account for keys in sm_1 that don't exist in sm_2.

[cLoque]

hi,

before i start asking questions again, i really would like to thank this forum, slowly I was able to form my program, (especially bartonc and bvdet for wasting their time reading my pathetic questions lol), im really glad that someone is helping me...

back to my questions...

i tried to use the items() but i have error saying:

line 17, in __add__
    for key, value in self.items():
AttributeError: GeneralSparse instance has no attribute 'items'

items() is another function right? but can't i just utilize my __setitem__ and __getitem__, because my __setitem__ already sets the value of my matrix (please correct me if i'm wrong), so because i have set

self.matrix[ij] = val

on my __setitem__ the value know of my self.matrix is equal to val...

i tried to look back on my __str__ method, and tried to pattern some idea then end up with this:

    def __add__(self, other):
        matrix = m() //i wrote it like this because it will implement my m class
        for i in range(self.row):// i like my code to check the row one by one 
            for j in range(self.col)://before jumping to the next row it has to check first each column that my row has and get the value of it
                self.matrix[i,j] = self[(i,j),0] + other[i,j]

this one didn't give me any error but it also didn't give me anythng, the output is like this:

[0  0  0  0  0  0  0  
 0  0  0  0  0  0  0  
 0  5  0  0  0  0  0  
 0  0  4  0  0  0  0  
 0  0  0  0  0  0  0  
 0  0  0  0  0  0  0  
 0  0  0  0  0  0  0  ]

[0  0  0  0  0  0  0  
 0  0  0  0  0  0  0  
 0  8  0  0  0  0  0  
 0  0  1  0  0  0  0  
 0  0  0  0  0  0  0  
 0  0  0  0  0  0  0  
 0  0  0  0  0  0  0  ]

None

i don't understand why it is giving me "NONE"

then i tried this one also:

self.matrix[i,j] = self[.get(i,j),0] + other[i,j]

python gave me this error:

line 19, in __add__
    self.matrix[i,j] = self.get[(i,j),0] + other[i,j]
AttributeError: GeneralSparse instance has no attribute 'get'

i don't know how to interpret the errors python's throwing me..hope you can help me how to figure it out

[bartonc]

hi,

i would like to add my two matrices, using __add__

class m:

    def __init__(self, mtx={}, m=0, n=0):
        self.matrix = {}
        self.matrix.update(mtx)
        self.row = m
        self.col = n

    def __getitem__(self, ij):
        return self.matrix.get(ij,0)

    def __setitem__(self, ij, val):
        self.matrix[i,j] = val

    def __add__(self, other):
        result = m()
        for i in other:
            self.result[i] = self.matrix.get(i, 0) + other[i]
        return result

but i always get an error.

Hope you can help me

[CODE=python]# don't forget that you may want to use print statements with your object
def __repr__(self):
return str(self.matrix )

def __getitem__(sel f, ij): # this is the syntax for calling with a tuple
return self.matrix.get (ij, 0)

def __setitem__(sel f, ij, val):
self.matrix[ij] = val # your version lacked consistance

sm_1 = sm({(0,0):5, (0,1):2})
sm_1[(0,2)] = 8
print sm_1
print sm_1[(0,2)][/CODE]

[cLoque]

[CODE=python]# don't forget that you may want to use print statements with your object
def __repr__(self):
return str(self.matrix )

def __getitem__(sel f, ij): # this is the syntax for calling with a tuple
return self.matrix.get (ij, 0)

def __setitem__(sel f, ij, val):
self.matrix[ij] = val # your version lacked consistance

sm_1 = sm({(0,0):5, (0,1):2})
sm_1[(0,2)] = 8
print sm_1
print sm_1[(0,2)][/CODE]

[CODE=python] def __getitem__(sel f, ij): # this is the syntax for calling with a tuple
return self.matrix.get (ij, 0)

def __setitem__(sel f, ij, val):
self.matrix[ij] = val # your version lacked consistance[/CODE]

what do you mean my version lacked consistence? do i need to add something? because what i understand about getitem and setitem is:

1. __getitem__ will get the index, if the dictionary that have been passed has no tuple it will assign 0 value but if it has then it will get the index or call the tuple

2. __setitem__ will take the index that __getitem__ got and assigned the value that the tuples has.

**please correct me if I am wrong**

[CODE=python]# don't forget that you may want to use print statements with your object[/CODE]

this is my __str__()


[CODE=python] def __str__(self):
s = "["
if self.row > 0:
for i in range(self.row) :
for j in range(self.col) :
s += str(self[i,j])
s += " "
if i < self.row-1:
s += "\n "
s += "]\n"
return s[/CODE]

isn't it that __str__() does the job in printing my code? because, for this program all we have to do is to complete the methods (__init__, __getitem__, __setitem__, __add__, __mul__, __str__)

thanks

[bartonc]

isn't it that __str__() does the job in printing my code?

Yes. That's correct. If there is not __str__(), then __repr__() gets called, though. It means "representation ".

[bartonc]

what do you mean my version lacked consistence?

Yours had a comma between i & j. There is no comma in mine (which I tested).

[bartonc]

this is my __str__()

Very nice .

[cLoque]

this is my whole program

class GeneralSparse:

    def __init__(self, mtx={}, m=0, n=0):
        self.matrix = {}
        self.matrix.update(mtx)
        self.row = m
        self.col = n

    def __getitem__(self, ij):
        return self.matrix.get(ij,0)

    def __setitem__(self, ij, val):
        self.matrix[ij] = val

    def __add__(self, other):
        matrix = GeneralSparse()
        for i in range(self.row):
            for j in range(self.col):
                self.matrix[i,j] = self[(i,j),0] + other[i,j]     

    def __str__(self):
        s = "["
        if self.row > 0:
            for i in range(self.row):
                for j in range(self.col):
                    s += str(self[i,j])
                    s += "  "
                if i < self.row-1:
                    s += "\n "
            s += "]\n"
            return s


if __name__=="__main__":
    x = GeneralSparse({(3,2):4, (2,1):5}, 7, 7)
    y = GeneralSparse({(3,2):1, (2,1):8}, 7, 7)
    print x
    print y
    a = x + y
    print a

so far everything works pretty fine. it displays my two matrices but doesn't add them up, and gives me "NONE"

i can't still seem to figure out what's wrong or missing in my __add__(). and why it doesn't work

[

[bartonc]

this is my whole program

class GeneralSparse:

    def __init__(self, mtx={}, m=0, n=0):
        self.matrix = {}
        self.matrix.update(mtx)
        self.row = m
        self.col = n

    def __getitem__(self, ij):
        return self.matrix.get(ij,0)

    def __setitem__(self, ij, val):
        self.matrix[ij] = val

    def __add__(self, other):
        matrix = GeneralSparse()
        for i in range(self.row):
            for j in range(self.col):
                self.matrix[i,j] = self[(i,j),0] + other[i,j]     

    def __str__(self):
        s = "["
        if self.row > 0:
            for i in range(self.row):
                for j in range(self.col):
                    s += str(self[i,j])
                    s += "  "
                if i < self.row-1:
                    s += "\n "
            s += "]\n"
            return s


if __name__=="__main__":
    x = GeneralSparse({(3,2):4, (2,1):5}, 7, 7)
    y = GeneralSparse({(3,2):1, (2,1):8}, 7, 7)
    print x
    print y
    a = x + y
    print a

so far everything works pretty fine. it displays my two matrices but doesn't add them up, and gives me "NONE"

i can't still seem to figure out what's wrong or missing in my __add__(). and why it doesn't work

[

You get None because you don't return a result. I've crafted an __add__() that may do more than you need, but you may learn a lot from these techniques:[CODE=python]#.....
def __add__(self, other):
res = sm({}, self.row, self.col)
for i in range(self.row) :
for j in range(self.col) :
try: # does the left hand matrix have this element?
mine = self.matrix[(i, j)]
# Yes. try to get() from other or use zero
res.matrix[(i, j)] = mine + other.matrix.ge t((i, j), 0)
except KeyError: # No, does the right hand one?
try:
# yes. add it to the resulting matrix
res.matrix[(i, j)] = other.matrix[(i, j)]
except KeyError: # No
pass # do nothing
return res

sm_1 = sm({(3,2):4, (2,1):5}, 7, 7)
sm_2 = sm({(3,2):1, (2,1):8}, 7, 7)
smSum = sm_1 + sm_2
print smSum
# this is from my repr() method
{(3, 2): 5, (2, 1): 13}[/CODE]Not that =python only go in the opening CODE tag. Thanks for paying attention to the post that you have seen in this regard.

[bartonc]

You get None because you don't return a result. I've crafted an __add__() that may do more than you need, but you may learn a lot from these techniques:[CODE=python]#.....
def __add__(self, other):
res = sm({}, self.row, self.col)
for i in range(self.row) :
for j in range(self.col) :
try: # does the left hand matrix have this element?
mine = self.matrix[(i, j)]
# Yes. try to get() from other or use zero
res.matrix[(i, j)] = mine + other.matrix.ge t((i, j), 0)
except KeyError: # No, does the right hand one?
try:
# yes. add it to the resulting matrix
res.matrix[(i, j)] = other.matrix[(i, j)]
except KeyError: # No
pass # do nothing
return res

sm_1 = sm({(3,2):4, (2,1):5}, 7, 7)
sm_2 = sm({(3,2):1, (2,1):8}, 7, 7)
smSum = sm_1 + sm_2
print smSum
# this is from my repr() method
{(3, 2): 5, (2, 1): 13}[/CODE]Not that =python only go in the opening CODE tag. Thanks for paying attention to the post that you have seen in this regard.

Here are some mods:[CODE=python]
#
def __getitem__(sel f, ij):
# Use self.matrix.get () if you really want zero for non-existent elements
return self.matrix[ij]
# If you don't use self.matrix.get () then you can eliminate matrix below (mostly)
# as shown here:

def __add__(self, other):
res = sm({}, self.row, self.col)
for i in range(self.row) :
for j in range(self.col) :
try: # does the left hand matrix have this element?
mine = self[(i, j)]
# Yes. try to get() from other or use zero
res[(i, j)] = mine + other.matrix.ge t((i, j), 0) # using a subclass avoids the .matrix
except KeyError: # No, does the right hand one?
try:
# yes. add it to the resulting matrix
res[(i, j)] = other[(i, j)]
except KeyError: # No
pass # do nothing
return res[/CODE]

[bartonc]

Here are some mods:[CODE=python]
#
def __getitem__(sel f, ij):
# Use self.matrix.get () if you really want zero for non-existent elements
return self.matrix[ij]
# If you don't use self.matrix.get () then you can eliminate matrix below (mostly)
# as shown here:

def __add__(self, other):
res = sm({}, self.row, self.col)
for i in range(self.row) :
for j in range(self.col) :
try: # does the left hand matrix have this element?
mine = self[(i, j)]
# Yes. try to get() from other or use zero
res[(i, j)] = mine + other.matrix.ge t((i, j), 0) # using a subclass avoids the .matrix
except KeyError: # No, does the right hand one?
try:
# yes. add it to the resulting matrix
res[(i, j)] = other[(i, j)]
except KeyError: # No
pass # do nothing
return res[/CODE]

And here it is as a subclass of built-in.dict using if and elif instead of nested try blocks:[CODE=python]
class smd(dict): # a dictionary like object
def __init__(self, mtx={}, m=0, n=0):
self.update(mtx )
self.row = m
self.col = n

def __add__(self, other):
res = smd({}, self.row, self.col)
for i in range(self.row) :
for j in range(self.col) :
if (i, j) in self: # does the left hand matrix have this element?
mine = self[(i, j)]
# Yes. try to get() from other or use zero
res[(i, j)] = mine + other.get((i, j), 0)
elif (i, j) in other: # No, does the right hand one?
# yes. add it to the resulting matrix
res[(i, j)] = other[(i, j)]
return res


sm_1 = smd({(3,2):4, (2,1):5, (2,2):6}, 7, 7)
sm_2 = smd({(3,2):1, (2,1):8, (4,4):6}, 7, 7)
smSum = sm_1 + sm_2
print smSum
# from dict.__str_()
{(3, 2): 5, (4, 4): 6, (2, 1): 13, (2, 2): 6}[/CODE]