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Complete this python program:
def make_system(A, M, x0, b, xtype=None):
assistant
#Here is the Python code you requested.

    """Make a linear system Ax=b
    Parameters
    A : LinearOperator
    sparse or dense matrix (or any valid input to aslinearoperator)
    M : {LinearOperator, Nones}
    preconditioner
    sparse or dense matrix (or any valid input to aslinearoperator)
    x0 : {array_like, None}
    initial guess to iterative method
    b : array_like
    right hand side
    xtype : {\f\, \d\, \F\, \D\, None}, optional
    dtype of the x vector
    Returns
    (A, M, x, b, postprocess)
    A : LinearOperator
    matrix of the linear system
    M : LinearOperator
    preconditioner
    x : rank 1 ndarray
    initial guess
    b : rank 1 ndarray
    right hand side
    postprocess : function
    converts the solution vector to the appropriate
    type and dimensions (e.g. (N,1) matrix)
    """
    A_ = A
    A = aslinearoperator(A)
    if (A.shape[0] != A.shape[1]):
        raise ValueError(('expected    square    matrix,    but    got    shape=%s' % (A.shape,)))
    N = A.shape[0]
    b = asanyarray(b)
    if (not ((b.shape == (N, 1)) or (b.shape == (N,)))):
        raise ValueError('A    and    b    have    incompatible    dimensions')
    if (b.dtype.char not in 'fdFD'):
        b = b.astype('d')
    def postprocess(x):
        if isinstance(b, matrix):
            x = asmatrix(x)
        return x.reshape(b.shape)
    if (xtype is None):
        if hasattr(A, 'dtype'):
            xtype = A.dtype.char
        else:
            xtype = A.matvec(b).dtype.char
        xtype = coerce(xtype, b.dtype.char)
    else:
        warn('Use    of    xtype    argument    is    deprecated.    Use    LinearOperator(    ...    ,    dtype=xtype)    instead.', DeprecationWarning)
        if (xtype == 0):
            xtype = b.dtype.char
        elif (xtype not in 'fdFD'):
            raise ValueError("xtype    must    be    'f',    'd',    'F',    or    'D'")
    b = asarray(b, dtype=xtype)
    b = b.ravel()
    if (x0 is None):
        x = zeros(N, dtype=xtype)
    else:
        x = array(x0, dtype=xtype)
        if (not ((x.shape == (N, 1)) or (x.shape == (N,)))):
            raise ValueError('A    and    x    have    incompatible    dimensions')
        x = x.ravel()
    if (M is None):
        if hasattr(A_, 'psolve'):
            psolve = A_.psolve
        else:
            psolve = id
        if hasattr(A_, 'rpsolve'):
            rpsolve = A_.rpsolve
        else:
            rpsolve = id
        if ((psolve is id) and (rpsolve is id)):
            M = IdentityOperator(shape=A.shape, dtype=A.dtype)
        else:
            M = LinearOperator(A.shape, matvec=psolve, rmatvec=rpsolve, dtype=A.dtype)
    else:
        M = aslinearoperator(M)
        if (A.shape != M.shape):
            raise ValueError('matrix    and    preconditioner    have    different    shapes')
    return (A, M, x, b, postprocess)