Python os operation

os.py

# For searching the file which name contains specific string in folder and sub folder
def search(s,t,mainpath):
    rootdir = mainpath
    searchpath = np.zeros(0)
    for parent, dirnames, filenames in os.walk(rootdir):
        for filename in filenames:
            if filename.find(s) != -1 and filename.find(t) != -1:
                searchpath = np.append(searchpath, 
                        os.path.abspath(os.path.join(parent,filename)))
    return searchpath