[Tutor] Matrix class problems

[Prahlad Vaidyanathan]

Hi,

    I have recently got back to exploring python, and, being a Maths
student, I decided to test my skills on a simple Matrix class. Now, I
came across some questions which I hope you will help clear.

    Firstly, I would like to know what exactly repr() does. I read the
docs, and this is what I got :

"""
>>> help(repr)
Help on built-in function repr:

repr(...)
repr(object) -> string

Return the canonical string representation of the object.
For most object types, eval(repr(object)) == object.
"""

What does this mean and how is this different from str() ?

Also, I wrote a __mul__() function, which looks like so :

"""
    def __mul__ (self, other) :
        if type(other) == type(0) :
            return self._scalar_multiply(other)
        else :
            return self._matrix_multiply(other)
"""

Now, this works, but like this :

"""
>>> import matrix
>>> m = matrix.Matrix([[1,0,0],[0,1,0],[0,0,1]])
>>> print (m*2)
[ 2, 0, 0 ]
[ 0, 2, 0 ]
[ 0, 0, 2 ]
>>> print (2*m)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: unsupported operand type(s) for *: 'int' and 'instance'

"""

    I understand that, in the first case, I am calling the function I
wrote, but in the second case I am calling the equivalent __mul__
function of an 'int' object. My question is, how do I make the latter
point to the former ? Although this is not a major issue, it bugs me
because I tend to write the number first, and the matrix later by habit.

    I hope I have been clear enough.

pv.

ps. For those of you who study Maths, I have been racking my brains as
to how to get the determinant of a Matrix, and have been unsuccessful.

How do I find the minor matrix ? Aaaarggghhh !!

-- 
Prahlad Vaidyanathan  <http://www.symonds.net/~prahladv/>

When things go well, expect something to explode, erode, collapse or
just disappear.