def transfer_documents(source_client, source_db, source_col, destin_client,
    destin_db, destin_col):
    """
    Transfer all documents from a collection in a MongoDB instance to another collection in another MongoDB instance
    inputs:
        source_client : Source pyMongo client
        source_db : Name of source DB
        source_col : Name of source collection
        destin_client : Destination pyMongo client
        destin_db : Name of destination DB
        destin_col : Name of destination collection
    """
    src_db = source_client[source_db]
    src_col = src_db[source_col]
    dest_db = destin_client[destin_db]
    dest_col = dest_db[destin_col]
    for document in src_col.find():
        dest_col.insert(document)
