Convert Pandas DataFrame to & from In-Memory Feath

Question

Using the IO tools in pandas it is possible to convert a DataFrame to an in-memory feather buffer:

import pandas as pd  
from io import BytesIO 

df = pd.DataFrame({'a': [1,2], 'b': [3.0,4.0]})  

buf = BytesIO()

df.to_feather(buf)

However, using the same buffer to convert back to a DataFrame

pd.read_feather(buf)

Results in an error:

ArrowInvalid: Not a feather file

How can a DataFrame be convert to an in-memory feather representation and, correspondingly, back to a DataFrame?

Thank you in advance for your consideration and response.

Answer 1

With pandas==0.25.2 this can be accomplished in the following way:

import pandas
import io
df = pandas.DataFrame(data={'a': [1, 2], 'b': [3.0, 4.0]})
buf = io.BytesIO()
df.to_feather(buf)
output = pandas.read_feather(buf)

Then a call to output.head(2) returns:

    a    b
 0  1  3.0
 1  2  4.0

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If you have a DataFrame with multiple indexes, you may see an error like

ValueError: feather does not support serializing for the index; you can .reset_index()to make the index into column(s)

In which case you need to call .reset_index() before to_feather, and call .set_index([...]) after read_feather

---

Last thing I would like to add, is that if you are doing something with the BytesIO, you need to seek back to 0 after writing the feather bytes. For example:

buffer = io.BytesIO()
df.reset_index(drop=False).to_feather(buffer)
buffer.seek(0)
s3_client.put_object(Body=buffer, Bucket='bucket', Key='file')