add comment on exercise about matrix implementation

add 2nd implementation with very tiny comparison between
the 2 implementations

source/Modules_and_Packages.rst

@@ -13,8 +13,12 @@ Exercise
 
 Implement a matrix and functions to handle it.
 choose the data structure of your choice.
-The API (**A**\ pplication **P**\ rogramming **I**\ nterface) to implemet is the following:
+The API (**A**\ pplication **P**\ rogramming **I**\ nterface) to implement is the following:
 
+We propose 2 implementations. These 2 implementations work with a list of lists as matrix modelling.
+But it is possible to implement it with a single list or a dict of list, ...
+
+The first implementation follow the api used explicit name for inner variables and good documentation. 
          
 .. literalinclude:: _static/code/matrix.py
    :linenos:
@@ -22,6 +26,27 @@ The API (**A**\ pplication **P**\ rogramming **I**\ nterface) to implemet is the
 
 :download:`matrix.py <_static/code/matrix.py>` .  
 
+But the problem with this implementation is, if we decide to change the inner model for a dixt of list for instance.
+We must reimplements most of the functions.
+
+In the following implementation we have only 4 functions that handle directly the lists. All other functions
+manipulate the matrix through these 4 functions. So if we change the inner model we will have to modifiy 
+only these functions. This implementation will be more maintainable.
+
+
+But this implementation use one letter names for inner variables and is poorly documented which not help
+to maintain or develop with this.
+
+The Best solution should be the second implementation but with the name of variables and documentation as in the firsr 
+implementation.
+
+.. literalinclude:: _static/code/matrix2.py
+   :linenos:
+   :language: python
+
+:download:`matrix2.py <_static/code/matrix2.py>` .
+
+
 Exercise
 --------
 

source/Scripting.rst

-.. _Scripting:
-
-
-*********
-Scripting
-*********

source/Variables.rst

-.. _Variables:
-
-************************************
-Variables, Expression and statements
-************************************
-
-
-Exercises
-=========
-
-Exercise
---------
-blabla
\ No newline at end of file

source/_static/code/matrix2.py

+# matrix is implemented by list of list
+def matrix_maker(ligne, col, val=None):
+	m = []
+	for i in range(ligne):
+		c = [val]*col
+		m.append(c)
+	return m
+
+#---- functions that depends on the matrix srtructure 
+
+def matrix_size(m):
+	return len(m), len(m[0])
+
+def matrix_get(matrix, i, j):
+	_check_matindex(matrix,i,j)
+	return matrix[i][j]
+
+def matrix_set(matrix, i, j, val):
+	_check_matindex(matrix,i,j)
+	matrix[i][j] = val
+
+def matrix_print(m):
+	im, jm = matrix_size(m) 
+	for i in range(im):
+		print m[i]
+
+
+
+#---- independant regarding matrix structure  
+def _check_matindex(matrix,i,j):
+	imax, jmax = matrix_size(matrix)
+	if (i < 0 or i >= imax) or (j < 0 or j>= jmax):
+		raise IndexError, "matrix index out of range"
+
+
+
+def matrix_get_line(matrix, i):
+	_check_matindex(matrix,i,0)
+	im, jm = matrix_size(matrix)
+	line = []
+	for n in range(jm):
+		line.append(matrix_get(matrix, i, n))
+	return line
+	
+def matrix_set_line(matrix, i, val):
+	_check_matindex(matrix,i,0)
+	im, jm = matrix_size(matrix)
+	for n in range(jm):
+		matrix_set(matrix, i, n, val)
+
+
+def matrix_get_col(matrix, j):
+	_check_matindex(matrix,0,j)
+	im, jm = matrix_size(matrix)
+	col = []
+	for n in range(im):
+		col.append(matrix_get(matrix, n, j))
+	return col
+	
+def matrix_set_col(matrix, j, val):
+	_check_matindex(matrix,0,j)
+	im, jm = matrix_size(matrix)
+	for n in range(im):
+		matrix_set(matrix, n, j, val)
+	
+	
+	
+if __name__ == '__main__':
+	m = matrix_maker(5, 3)
+	matrix_set(m,0, 0, 1)
+	matrix_set(m,0, 2, 2)
+	matrix_set(m,4, 0, 12)
+	matrix_set(m,4, 2, 15)
+	matrix_print(m)
+	print "get line 0",  matrix_get_line(m, 0)
+	print "get col 0", matrix_get_col(m, 0)
+