def make_source_str(layer_name):
    """
    Create a string value representing a Python list of source layers

    Parameters
    ----------
    layer_name : string
       List of Python layer names

    Returns
    -------
    string
        String representation of list of Python layer names

    """
    source_str = []
    for ii in range(len(layer_name)):
        source_str.append(layer_name[ii])
    return repr(source_str)
