Datatype cannot be written to CSV

I want to a write big decimal to a CSV file that looks like this:

'''
pyarrow.decimal128(int precision, int scale=0) -> 
pl.Decimal(scale: int, precision: int | None = None)
'''
df = DataFrame(
    data={'BIG_DECIMAL': [Decimal(216106296082069775206775124.4217024184)]},
    schema={'BIG_DECIMAL': pl.Decimal(10, 38)}
)

df.write_csv('file.csv')

However, when I run it, I get an error that says:

datatype 216106296082069783127785472 cannot be written to csv

What is the problem?

The error you're encountering indicates that the datatype of your big decimal value cannot be directly written to a CSV file using the default CSV writer. The CSV writer in pandas doesn't have built-in support for handling custom datatypes like pyarrow.decimal128.

To overcome this issue, you can convert the big decimal values to a compatible datatype that can be written to a CSV file. One option is to convert the big decimal values to strings before writing them to the CSV file. Here's an updated version of your code that converts the big decimal value to a string:

 import polars as pl


    df = pl.DataFrame({
        'BIG_DECIMAL': [pl.Decimal('216106296082069775206775124.4217024184')]
    })
    
    
    df = df.with_column(df['BIG_DECIMAL'].map(lambda dec: str(dec)))
    
    
    df.write_csv('file.csv')