Problems with append to output in PySpark

Question

Have a problem with output file. Everytime I start my program, it needs to write down an answer to the dataframe in a new row in string format. (Output example: 1,5,14,45,99.) My task needs to be automatically checked by program like

PYSPARK_PYTHON=/opt/conda/envs/dsenv/bin/python spark-submit \
    --master yarn \
    --name checker \
    projects/3/shortest_path.py 12 34 /datasets/twitter/twitter.tsv hw3_output

This program returns output file with only one row. But on my local notebook it works even with several runs. Here is a part of my program that works with output

output = sys.argv(4)
d = [[answer]]
df_out = spark.createDataFrame(data=d)
df_out.write.format("csv").options(delimiter='\n').mode('append').save(output)

Can you please suggest a way to modify my program or make suggestions what goes wrong?

Tried to change options of .save in dozens of combinations.