[BUG]write_delta({'custom_metadata':str}) cannot be converted. str to pyDict error (0.18.2_DeltaPython/Windows10)

[starzar]

Bug

0.18.2_DeltaPython/Windows10

• Spark
• [x ] Standalone
• Flink
• Kernel
• Other (fill in here)

Describe the problem

write_deltalake_pyarrow(TypeError: argument 'custom_metadata': 'str' object cannot be converted to 'PyDict'

Steps to reproduce

import polars as pl
import datetime
datetime_cur = datetime.datetime.now()
datetime_cur_str = datetime_cur.strftime("%Y-%m-%d")
data = {
    "timestamp": [datetime_cur, datetime_cur + datetime.timedelta(days=1)],
    "alphabet": ["A", "B"]
}

_df = pl.DataFrame(data)

print(_df)
print('datetime_cur_str')
print(type(datetime_cur_str))
print(datetime_cur_str)
_deltapath = r'Others/Polars/tests'

# error occurs for both engines : 'engine': 'pyarrow'/'rust'
_df.write_delta(target=_deltapath, mode="overwrite", overwrite_schema=False,
                            delta_write_options={'engine': 'pyarrow', 'custom_metadata': datetime_cur_str})

-->

Observed results

Traceback (most recent call last):
  File "C:\Users\User_0\Documents\Code\Python\NseScraping\Others\Polars\tests\deltalake1.py", line 20, in <module>
    _df.write_delta(target=_deltapath, mode="overwrite", overwrite_schema=False,
  File "C:\Users\User_0\AppData\Local\Programs\Python\Python312\Lib\site-packages\polars\dataframe\frame.py", line 3877, in write_delta
    write_deltalake(
  File "C:\Users\User_0\AppData\Local\Programs\Python\Python312\Lib\site-packages\deltalake\writer.py", line 543, in write_deltalake
    write_deltalake_pyarrow(
TypeError: argument 'custom_metadata': 'str' object cannot be converted to 'PyDict'

Expected results

Further details

Environment information

• Delta Lake version:
• Spark version:
• Scala version:

Willingness to contribute

The Delta Lake Community encourages bug fix contributions. Would you or another member of your organization be willing to contribute a fix for this bug to the Delta Lake code base?

• Yes. I can contribute a fix for this bug independently.
• Yes. I would be willing to contribute a fix for this bug with guidance from the Delta Lake community.
• No. I cannot contribute a bug fix at this time.

[MrPowers]

Thanks for opening this! Looks like this is for the delta-rs repo, going to transfer this issue now.

[ion-elgreco]

@starzar this isn't a bug. Custom metadata takes a dict[str,str] as value