Why does this padding function work alone but not as a PySpark UDF?

I have the following function:

Why does this padding function work alone but not as a PySpark UDF?

I have the following function:

Why does this padding function work alone but not as a PySpark UDF?

I have the following function:

Why does this padding function work alone but not as a PySpark UDF?

I have the following function:

Why does this padding function work alone but not as a PySpark UDF?

I have the following function:

Why does this padding function work alone but not as a PySpark UDF?

I have the following function: