Python function to build a block matrix

Sometimes it is useful to build a matrix from matrices forming blocks of the former one.

As I understand, neither numpy nor scipy implement this functionality. Scipy has the scipy.linalg.special_matrices.block_diag function, but it only admits blocks along the diagonal. The following function builds a matrix from the elements of the input list a, as long as their dimension is compatible.

 def blockmat(a):  
   n=size(a,0)  
   N=size(a[0],1)  
   sqn=sqrt(n)  
   ind=0  
   rows=[]  
   cols=[]  
   for i in range(0,n):  
     A=a[i]  
     M=size(A,0)  
     #if (M != N):  
     #  return -1   
     if ((i>0) & (i%int(sqn) == 0)):  
       rows.append(numpy.concatenate(cols,axis=0))  
       cols=[]     
     cols.append(A)  
   rows.append(numpy.concatenate(cols,axis=0))  
   return numpy.concatenate(rows,axis=1)