I use [this](https://stackoverflow.com/questions/31898964/how-to-write-the-resulting-rdd-to-a-csv-file-in-spark-python) method to write csv file. But it will generate a file with multiple part files. That is not what I want; I need it in one file. And I also found [another post](https://dzone.com/articles/spark-write-csv-file) using scala to force everything to be calculated on one partition, then get one file. 

**First question: how to achieve this in Python?** 

In the second post, it is also said a `Hadoop function` could merge multiple files into one. 

**Second question: is it possible merge two file in Spark?**