__Add__ matrices method in python 2.7
I am new to Python, so I need your help. The program must add and subtract random matrices.
import random
class Matrix:
def __init__(self):
self.mat = [[]]
def gen_ran_numb(self,row=5,col=5):
self.mat=[[random.randint(0,10) for z in xrange(col)] for z in xrange(row)]
def print_matrix(self):
print self.mat
def __add__(self,b):
mat=[]
for j in range(len(self.mat)):
temp=[]
for k in range(len(self.mat[0])):
x=self.mat[j][k] + b.mat[j][k]
temp.append(x)
mat.append(temp)
rez=mat
return rez
def __sub__(self,b):
mat=[]
for j in range(len(self.mat)):
temp=[]
for k in range(len(self.mat)):
x=self.mat[j][k] - b.mat[j][k]
temp.append(x)
mat.append(temp)
return mat
a=Matrix()
b=Matrix()
c=Matrix()
a.print_matrix()
a.gen_ran_numb(5,5)
b.gen_ran_numb(5,5)
c.gen_ran_numb(5,5)
a.print_matrix()
b.print_matrix()
c.print_matrix()
print b+a
print b+a+c
If I add 2 matrices it works fine, but if I add 3 or 4 matrices I took this error:
Traceback (most recent call last):
File "C:/Users//Documents/Python/task.py", line 40, in <module>
print b+a+c
TypeError: can only concatenate list (not "instance") to list
I don't understand what I am doing wrong. Please help me. Thank!
source to share
The problem is that you are not returning an object Matrix
, but an actual matrix, i.e. list of lists. So when you are concatenating 2 objects that is fine, but when you are doing it with 3 objects you are actually trying to concatenate the list object with the object Matrix
.
In other words, just change the function to return a new instance, like this:
def __add__(self, b):
res = Matrix()
res.mat = [] #to avoid an unwanted empty list at the beginning of new matrix
for j in range(len(self.mat)):
temp = []
for k in range(len(self.mat[j])):
x = self.mat[j][k] + b.mat[j][k]
temp.append(x)
res.mat.append(temp)
return res
You will probably want to change too __sub__
.
source to share