human
Solve the following python programming problem given the following code:
def guvectorize(ftylist, signature, **kws) : 
    'guvectorize(ftylist, signature, target=\'cpu\', identity=None, **kws)

    A decorator to create numpy generialized-ufunc object from Numba compiled
    code.

    Args
    -----
    ftylist: iterable
        An iterable of type signatures, which are either
        function type object or a string describing the
        function type.

    signature: str
        A NumPy generialized-ufunc signature.
        e.g. "(m, n), (n, p)->(m, p)"

    identity: int, str, or None
        The identity (or unit) value for the element-wise function
        being implemented.  Allowed values are None (the default), 0, 1,
        and "reorderable".

    target: str
            A string for code generation target.  Defaults to "cpu".

    Returns
    --------

    A NumPy generialized universal-function

    Example
    -------
        @guvectorize([\'void(int32[:,:], int32[:,:], int32[:,:])\',
                      \'void(float32[:,:], float32[:,:], float32[:,:])\'],
                      \'(x, y),(x, y)->(x, y)\')
        def add_2d_array(a, b):
            for i in range(c.shape[0]):
                for j in range(c.shape[1]):
                    c[i, j] = a[i, j] + b[i, j]

    ' 
    if isinstance (signature, str) : 
        ftylist = [ftylist] 
def wrap(func) : 
        guvec = GUVectorize (func, signature, ** kws) 
        for fty in ftylist : 
            guvec.add (fty) 
return guvec.build_ufunc () 
return wrap 

    
    

    Fix the buggy line: if isinstance (signature, str) :
assistant
#Here is Python program to fix the buggy line: if isinstance (signature, str) :
.

if isinstance (ftylist, str) :