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Added the new system to the Iceberg connection only to keep this smaller. The idea is to add the decorator to all other connectors, happy to do it here or in a follow up PR.

@datapythonista datapythonista requested a review from noatamir as a code owner June 12, 2025 21:58
@datapythonista datapythonista added IO Data IO issues that don't fit into a more specific label API Design labels Jun 12, 2025
method on it with the arguments provided by the user (except the ``engine`` parameter).

To avoid conflicts in the names of engines, we keep an "IO engines" section in our
[Ecosystem page](https://pandas.pydata.org/community/ecosystem.html#io-engines).
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This will need different formatting since rst hyperlink syntax is different from md

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True, thanks for the heads up. I updated it.

@@ -52,6 +56,10 @@ def read_iceberg(
scan_properties : dict of {str: obj}, optional
Additional Table properties as a dictionary of string key value pairs to use
for this scan.
engine : str, optional
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Should the read_* and to_* signatures also have an engine_kwargs: dict[str, Any] | None argument to allow specific engine arguments to be passes per implementation?

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Very good point. In read_parquet we already have a **kwargs for engine specific arguments. In map, apply... it's a normal engine_kwargs since **kwargs is used in some cases for the udf keyword arguments. I think for IO readers/writers **kwargs as read_parquet does is fine.

I didn't want to add the engine to all connectors in this PR to keep it simpler, but I'm planning to follow up with another PR that adds it, and adds **kwargs for connectors where it's not there already. Surely happy to add both things here if you prefer, just thought it would make reviewing simpler to keep the implementation separate from all the changes to parameters.

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if engine-specific kwargs are needed, isn't that a good reason to use engine.read_whatever(path, **kwargs) instead of pd.read_[...]?

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This is a good point. Thinking about readers we don't care about I think what you propose is the best choice. And this PR doesn't really prevent that from happening anyway. But for readers we cared enough to include in pandas, I think this new interface offers an advantage. For example, there was some discussion on whether we should move the fastparquet engine out of pandas, Patrick suggested it. I think this interface allows moving the fastparquet engine to the fastparquet package, users with fastparquet installed will still have it available in the same way as it is now, but we can forget about it.

Of course discussions about moving readers out of pandas will have to happen later. But this interface seems quite useful and it's very simple, so in my opinion it's a good deal.

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/preview

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Website preview of this PR available at: https://pandas.pydata.org/preview/pandas-dev/pandas/61642/

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@mroeschke I addressed your comments and I think this should be ready when you've got time. Thanks!

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Overall I think this is a good idea. Might be good to get another opinion to vet the idea.

I think still having a **kwargs like argument so users can pass engine specific arguments without manually expanding the pandas signatures would be good. But since this is for the new IO method iceberg, it's not as critical now.

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Fully agree, I just didn't want to make this PR too big by allowing the engines and adding**kwargs everywhere here. I'll do it in a follow up.

@pandas-dev/pandas-core any opinion or comment before merging this?

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WillAyd commented Jun 26, 2025

Thanks for the ping. I haven't been involved enough to really block, but I'm curious what the advantage of this is over leveraging the Arrow PyCapsule interface for data exchange; I feel like the latter would be a better thing to build against, given it is a rather well adopted standard in the ecosystem

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Good point, thanks for the feedback. I think this is a higher interface that still allows for using the Arrow pycapsule internally. Surely an option would be to get rid of I/O in pandas, and have an ecosystem of readers that can be used via a single pd.read(engine) or something similar. But I think it's better to use the current API, allow third party engines as implemented here, and let the engines decide how the data is exchanged. Or what is your idea?

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WillAyd commented Jun 26, 2025

It would depend on a resolution to #59631, but for demo purposes let's assume we decide to implement a new DataFrame.from_pycapsule class method.

So instead of an I/O method like:

df = pd.read_iceberg(..., kwargs)

You could construct a dataframe like:

df = pd.DataFrame.from_pycapsule(
    # whatever the iceberg API is here to create a table
    pyiceberg.table(..., kwargs)
)

The main downside is verbosity, but the upsides are:

  1. Generic approach to read any datasource
  2. pandas itself has to do very little development (third parties are responsible for integration)
  3. polars, cudf, etc... all benefit in kind

So yea this could be extended to say even Delta if they decided to implement the PyCapsule interface (whether they do currently or not, I don't know):

df = pd.DataFrame.from_pycapsule(
    # whatever the delta API is here to create a table
    DeltaLake.table(..., kwargs)
)

and if polars decided on the same API you could create that dataframe as well:

df = pl.DataFrame.from_pycapsule(
    # whatever the delta API is here to create a table
    DeltaLake.table(..., kwargs)
)

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WillAyd commented Jun 26, 2025

As I said though, I haven't been involved enough to really block, so if this PR has some support happy to roll with it and can clean up later if it comes to it. Thanks for giving it consideration @datapythonista

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i don't know anything about pycapsules. is that effectively a pd.from_arrow_table method that isn't pyarrow-specific?

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WillAyd commented Jun 26, 2025

Yea kind of. In a generic sense, a PyCapsule is just a Python construct that can wrap generic memory. The Arrow PyCapsule interface further defines lifetime semantics for passing Arrow data across a PyCapsule:

https://arrow.apache.org/docs/format/CDataInterface/PyCapsuleInterface.html

Somewhat separately there is the question of how you would read and write the data in a capsule. For pandas that is pyarrow, but other libraries may choose a tool like nanoarrow for a smaller dependency

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@WillAyd what you propose seems reasonable, but I guess we aren't planning to remove all pandas IO anytime soon. And if we keep our readers and writers with multiengine support, I think this interface is going to be useful, even if long term we move into the pyarrow capsule reader you propose. Also, since pandas is not arrow based yet, this PR could be used to move the xarray connectors to the xarray package, while using pycapsule wouldn't be ideal for pandas/xarray interchange, as they are numpy based.

Dr-Irv
Dr-Irv previously requested changes Jun 26, 2025
Comment on lines +531 to +536
it. This is done in ``pyproject.toml``:

```toml
[project.entry-points."pandas.io_engine"]
empty = empty_data:EmptyDataEngine
```
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I'm not 100% sure if this can happen, but what if the project isn't using pyproject.toml for some reason. Is there another way to do the configuration or is using pyproject.toml required?

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Entry points existed before pyproject.toml, and can also be added to setup.py. it makes no difference how the package defines them, pip or conda will add the entry point to the environment registry, and pandas will be able to find them regardless of how the project created them.

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The language here suggests that the only way to add the entry point is via pyproject.toml. If this is the recommended way, we can say that. Or if other ways are supported, we should show that too.

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pyproject.toml is the way to do it, setup.py is how it was done in the past. I'm sure people reading this will be able to figure out how this was done in the past if their code is still using setup.py

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Would having the entry point being a module variable like in the UDF engine PR address some of the concerns about using pyproject.toml ?

@@ -90,6 +90,7 @@ Other enhancements
- Support passing a :class:`Iterable[Hashable]` input to :meth:`DataFrame.drop_duplicates` (:issue:`59237`)
- Support reading Stata 102-format (Stata 1) dta files (:issue:`58978`)
- Support reading Stata 110-format (Stata 7) dta files (:issue:`47176`)
- Third-party packages can now register engines that can be used in pandas I/O operations :func:`read_iceberg` and :meth:`DataFrame.to_iceberg` (:issue:`61584`)
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This sentence makes it seem that it only applies to read_iceberg . But doesn't the engine comment apply to ANY of the current IO routines that have an engine argument?

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Good point. This PR creates the new system for third party engines in a generic way, and the idea is to use it everywhere, but the PR only applies it to iceberg for now. The reason is to make reviewing easier, as adding the engine keyword to mamy connectors will make the PR significantly bigger.

My idea is to add the whatsnew note for what's delivered in this PR, and in the follow up PR update it to what you suggest.

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Actually, since read_iceberg() and to_iceberg() are new for 3.0 anyway, I don't think you need a whatsnew item for this PR, because, as you say, it is just functionality that applies to iceberg right now. Then, if it is accepted, you can add a whatsnew to point to all the readers/writers that support it, if you add support for those readers/writers.

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I think it's a good practice to make PRs atomic, and don't assume things about other PRs. If we were going to release just after this commit, things would be correct. As said, the follow up PR will update the whatsnew.

Comment on lines +1342 to +1349
package_name = entry_point.dist.metadata["Name"]
else:
package_name = None
if entry_point.name in _io_engines:
_io_engines[entry_point.name]._packages.append(package_name)
else:
_io_engines[entry_point.name] = entry_point.load()
_io_engines[entry_point.name]._packages = [package_name]
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I have to wonder if it is better to just get the entry points here but NOT load them., and then load them on demand. So the dict would just have EntryPoint objects, or a tuple of EntryPoint and package names.

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Sounds like a good idea, I didn't think about it before. I think it'll make the code slightly more complex, but not loading the code of unused connectors would be nice, in case a package takes a long time to run.

I won't be updating this PR, as I don't think it's likely that it'll be merged, so not worth the effort. But I'd be happy to implement it in a follow up.

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And if we keep our readers and writers with multiengine support

ATM that's just csv and parquet? And the parquet one plausibly is not needed?

AFAICT this adds a bunch of new tests/code/docs, complicates the import with entrypoints, and lets 3rd parties hijack our namespace. All when there's a perfectly good option of using their own namespace.

Also if we ever did change defaults like #61618 or PDEP16, that would Break The World for any 3rd party readers that we are implicitly committed to supporting.

-1.

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WillAyd commented Jun 26, 2025

Also, since pandas is not arrow based yet, this PR could be used to move the xarray connectors to the xarray package, while using pycapsule wouldn't be ideal for pandas/xarray interchange, as they are numpy based.

Definitely not an expert, but I want to point out that DLPack also offers a PyCapsule for data exchange. See https://dmlc.github.io/dlpack/latest/python_spec.html

So depending on how generic we want things to be, PyCapsule support doesn't just mean consuming Arrow data, but could mean dlpack data as well (which I assume xarray can do, if it doesn't already)

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ATM that's just csv and parquet? And the parquet one plausibly is not needed?

Any reader could have an engine option, this would allow having xarray, sas... as other packages.

AFAICT this adds a bunch of new tests/code/docs, complicates the import with entrypoints, and lets 3rd parties hijack our namespace. All when there's a perfectly good option of using their own namespace.

This adds minimal tests, code or docs, any other PR adds as many as this. We already allow entrypoints in pandas, and 3rd parties can not use this to change the namespace directly, just to allow engine="foo".

Also if we ever did change defaults like #61618 or PDEP16, that would Break The World for any 3rd party readers that we are implicitly committed to supporting.

We could add the value of the flag setting the types to use to the interface, so third parties can transition in the same way as us.

-1.

Being honest I think you'll block anything that is Bodo related. I think it was best to be -1 to accept their money when they offered it. In any case, I'll close this, and I'll open a separate issue to discuss returning the remaining funds, as I think it can make sense at this point.

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Dr-Irv commented Jun 28, 2025

FWIW I'm pretty comfortable being the "that doesn't need a full PDEP" guy.

As the person usually asking for a PDEP, I don't think one is needed here.

But @jbrockmendel brings up some valid concerns, and I leave it to others to determine whether those concerns mean we don't accept this addition to pandas.

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Thanks @jbrockmendel, this is helpful, I understand better your concerns, and I actually agree in two of your point.

While I think this is actually a very small change, it wouldn't be worth if the goal was to allow Bodo (or others) to write a reader. We got rid of read_gbq long ago, because maintenance of just the wrapper was annoying, and also not an open source format, but a paid infra. They implemented pandas_gbq.read_gbq, and no big deal. That was a whole format, not an engine, but we could do the same with anything.

I just find this has some advantages:

  • For writers, what you propose doesn't support method chaining
  • With your proposal, if I want to get rid of the xarray IO code in pandas, it's a breaking change. With this proposal I can move the wrapper to xarray, add the entrypoint, and users with xarray installed won't see a difference. Users without xarray may see a different error message if using xarray. And our CI wouldn't need to test for xarray, and more important, our environment wouldn't have xarray. If we can do this with few engines, I'll probably won't have to continue spending countless hours fighting with the problems of the conda solver.
  • If our CSV readers (or Excel readers) were moved out to other packages, with your proposal their signatures would become independent. And changing from one engine to another would require changing the module, possibly the function name, and the parameters. With this PR it'd be just the engine name, and parameters only if engine specific parameters exist. For context, I'd like to have pandas CSV engines for Polars and DuckDB, and I'd like that the code lives in those projects. This PR (and the needed follow up to support all formats) would allow it from the pandas side.

Second point I agree is that users may not immediately underatand that the engines don't live in pandas. I don't have a solution, but two things to consider.

  • For most connectors the code already lives in an external package, we just maintain a thin wrapper. So, in a way, we already take responsibility for other packages code.
  • The docs won't mention external engines, but the API docs can mention external engines are supoorted, as well as the user guide. For new engines, I think users will have to learn them from the other packages docs, or our ecosystem page. So, except for the users that read code written by someone else, I think most users can become familiar with the idea that enginea are not part of pandas.

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For writers, what you propose doesn't support method chaining

A user who is heroin-level obsessed with method chaining can use .pipe(bodo.to_iceberg)

if I want to get rid of the xarray IO code in pandas

If that is the real goal here, please just make an issue for that. In that scenario, I would also say that the relevant reader/writer belongs in its own namespace.

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@twoertwein we discussed supporting what you mention in PDEP-9. And if people aren't convinced to have this for engines only, I don't think there can be consensus for supporring aebitrary formats in the pandas namespace.

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If that is the real goal here, please just make an issue for that.

I wouldn't say it's the real goal, but surely one of the main reasons. I wrote PDEP-9 to go into the details on why I think pandas IO should work as Python modules.

I think the main reason why people use Python is because code is readable, and it's batteries included via pip/conda. I'd say people use pandas because it's a Swiss knife, also with everything included. If a user in Python is asked to implement code in a C extension, is like telling them it's not possible, because they are used to pip install + import. In a similar way (in my opinion), telling users to import another module to read, and pipe to write, is telling them the reader is not supported by pandas. Surely the difficulty is not comparable to writing a C extension, but the feeling that is not supported and that a hack is needed are probably the same.

The real goal here is to reduce the gap between a pandas core IO connector, and an external IO connector. To the same as a standard library package and a cheeseshop package. And one of the main motivations is that moving IO connectors into and out of pandas would become trivial, both technically and in terms of backward compatibility. PDEP-9 tried that fully, this is just for engines of pandas supported formats. But same idea, just that this PR is trivial, both in code and conceptually, and PDEP-9 came with problems of naming conflicts, pollution of the pandas namespace.

But I personally don't think discussing again PDEP-9 is needed. I think it's mostly whether the advantages here are worth the added complexity. To me that's an absolute yes. I guess you don't see the advantages as significant as you think it's fine to just use pandas modules and pipe. I disagree with that, but it's surely a valid point of view. In practice we won't move any IO connector out of pandas with this PR. But it's surely not clear if that was going to happen anyway, so not an immediate advantage.

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@Dr-Irv you are still blocking this PR. Is it that you want it to be blocked, or that you forgot to remove the requested change flag? From your last comment I can't tell which of Brock's comments you share, amd if they are a blocker. But if you just didn't forgot to remove the flag, I don't think it's very nice to block someone's work without being clear what change is expected, or why this shouldn't be merged in any form.

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is telling them the reader is not supported by pandas

Correct. It's implemented and maintained by a 3rd party. That is the correct message to send.

To the same as a standard library package and a cheeseshop package

Using a 3rd party engine via their own namespace is literally using a cheeseshop package.

or why this shouldn't be merged in any form

Regardless of whether Irv removes the block, please do not self-merge.

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Dr-Irv commented Jun 30, 2025

@Dr-Irv you are still blocking this PR. Is it that you want it to be blocked, or that you forgot to remove the requested change flag? From your last comment I can't tell which of Brock's comments you share, amd if they are a blocker. But if you just didn't forgot to remove the flag, I don't think it's very nice to block someone's work without being clear what change is expected, or why this shouldn't be merged in any form.

I have comments above that still should be addressed:

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Thanks @Dr-Irv for your comment, and thanks for reminding me that you'll continue to block other people's work based on zero impact and extremely opinionated details that I'd bet only make sense to you.

I guess my options are letting you blackmail me so your ego is happy, report your behaviours to the CoC or the steering committe you are part ot it. Or stop wasting my time in the toxic environment pandas has become. I think the choice is clear, so take this as a good bye.

Comment on lines +531 to +536
it. This is done in ``pyproject.toml``:

```toml
[project.entry-points."pandas.io_engine"]
empty = empty_data:EmptyDataEngine
```
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pyproject.toml is the way to do it, setup.py is how it was done in the past. I'm sure people reading this will be able to figure out how this was done in the past if their code is still using setup.py

@@ -90,6 +90,7 @@ Other enhancements
- Support passing a :class:`Iterable[Hashable]` input to :meth:`DataFrame.drop_duplicates` (:issue:`59237`)
- Support reading Stata 102-format (Stata 1) dta files (:issue:`58978`)
- Support reading Stata 110-format (Stata 7) dta files (:issue:`47176`)
- Third-party packages can now register engines that can be used in pandas I/O operations :func:`read_iceberg` and :meth:`DataFrame.to_iceberg` (:issue:`61584`)
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I think it's a good practice to make PRs atomic, and don't assume things about other PRs. If we were going to release just after this commit, things would be correct. As said, the follow up PR will update the whatsnew.

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Dr-Irv commented Jun 30, 2025

Thanks @Dr-Irv for your comment, and thanks for reminding me that you'll continue to block other people's work based on zero impact and extremely opinionated details that I'd bet only make sense to you.

I'm sorry that you see my comments in that light. That's certainly not my intent.

I guess my options are letting you blackmail me so your ego is happy, report your behaviours to the CoC or the steering committe you are part ot it. Or stop wasting my time in the toxic environment pandas has become. I think the choice is clear, so take this as a good bye.

I am not trying to blackmail you. I am providing what I believe to be constructive comments to make the work you do understandable by others.

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I wanted to add my perspective on this PR. I work at Bodo, but before that I was a user of Pandas myself.

I think that having the engine argument in Pandas as well as the corresponding docs page offers an easy way for users to solve their problems without researching other packages or workarounds. For example, reading multiple csv files from a directory. A Pandas user might write code that looks like this:

import glob
import pandas as pd

path = "my_dir"
filenames = glob.glob(path + "/*.csv")
dfs = []

for file in glob.glob(path + "/*.csv"):
    dfs.append(pd.read_csv(file))

pd.concat(dfs, ignore_index=True)

But with the engine param and corresponding docs, they could discover changing the engine might simplify this workflow:

import pandas as pd

pd.read_csv("my_dir/*.csv", engine="some_engine")

Of course if they truly were bothered by this they could do some googling or ask AI and find another package that fits their use case a bit better, but I feel like Pandas should lead users in the right direction.

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Dr-Irv commented Jul 2, 2025

I have comments above that still should be addressed:

@datapythonista Just to clarify, I'm not for or against adding this particular feature. The comments that I was hoping you would respond to were about documentation and performance. With respect to the documentation, I think it can be improved (and would be helpful if this were to be reopened and merged in). With respect to performance, you acknowledged that delayed loading is a good idea, but you didn't want to do it because you didn't think the PR would be accepted.

I'm not making the decision of accepting and merging the PR if you were to reopen it. I will leave that to others.

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But with the engine param and corresponding docs, they could discover changing the engine might simplify this workflow:

  1. I don't think we're putting the docs for third party engines in our docs.
  2. A third party engine with behavior significantly different from the pandas API doubly doesn't belong in the pandas namespace.

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Thanks @Dr-Irv for you comment. I think there are two separate things we are talking about.

About the specific feedback, I think loading the engines lazily is great feedback, and I surely want to incorporate it here. As said, I don't think it make sense to spend the time on it just now, since Brock has some other concerns. And I guess nobody else probably spend enough time fixing the CI for read_clipboard or trying to make the conda solver resolve our dependencies fast, to share my excitement about moving some of the IO connectors to third-party packages. There wasn't much interest when I opened PDEP-9, and there hasn't been anyone very positive in this minimal version of it. So, this is not a problem. I think it makes more sense to take care of in a follow up, but if this PR is merged, we'll load the engines lazily, as it's surely better than the current implementation.

Removing the release note here, and adding it in the follow up PR is also fine. Also adding information on how to add an entrypoint for setup.py users. I personally prefer how things are now, and I understand that you have a preference for what you suggest. I don't think there is even one option clearly better than another, just taste, and anything would be fine.

So, the second thing we're talking about, is about blocking other people's PRs. I think blocking PRs is a useful tool we have, and I surely use it when needed. For example, if a PR is going to cause us future trouble, in our CI, with too much technical debt, with a poor experience for the users... I think it's great that we all can block PRs until the concerns are resolved. But for some reason, you seem to be abusing blocking PRs recently (at least in my opinion). If you agree with my comments about this PR above, you are literally not letting this PR be merged until I implement your (in my opinion) very opinionated and not very important comments of removing a release note that as I told you will be updated later. And to add an explanation about how to also add entry points with the legacy setup.py. If you share those as suggestions, I appreciate them, as I think it's good feedback. If other people agree with you, I'll be happy to update the PR with them. But if you block a PR for such trivial topics, it feels like you're making pandas your personal project, and that no work in pandas will be possible unless it follows your personal preferences. If that's the case, and pandas is happy with this sort of behavior, I surely don't want to continue contributing to it.

And this already happened recently in the df.select("col1", "col2"), which I think it's the same exact case.

I don't think we're putting the docs for third party engines in our docs.
A third party engine with behavior significantly different from the pandas API doubly doesn't belong in the pandas namespace.

Agree on not having third party engines in the docs (except for the Ecosystem page in our website).

As opposed to PDEP-9, this PR tries to unify the behavior of readers/writers of the same format. I agree it'd be better for users if third-party connectors have consistency with the file path (accepting urls, compressed files, cloud files...). I'm not too sure if enforcing it is feasible or the best option. Maybe having it recommended in the docs, with info on how to support the standard pandas syntactic sugar is the best approach.

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read_clipboard

ironically i'd be fine with deprecating this (xref #56039)

is about blocking other people's PRs

I don't see why it is relevant whether someone has hit the the "block" button since the informal norm is to not merge until there is consensus. For all their faults, PDEPs have a lower bar to acceptance than the informal system.

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I don't see why it is relevant whether someone has hit the the "block" button since the informal norm is to not merge until there is consensus.

If I start blocking every PR for small details that I would do differently than in the PR, nothing is probably going to be merged again in pandas. And we aren't too far from this situation lately. Any PR that gets enough attention is likely to not move forward.

This is what all this is about to me. If a small PR like this one, with no backward-compatibility issues, small and simple code, and with a huge potential (IMHO) can't be merged because there are different opinions on when to add the release note, I think we are wasting our time.

@jbrockmendel
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jbrockmendel commented Jul 3, 2025

It can’t be merged because I’m strongly against it and you need to get a consensus of the not-me team members to get me to say “oh well”

@datapythonista
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I know, this is a different discussion than what I'm saying about @Dr-Irv blocking PRs.

But clearly an equal impediment to pandas progress. But we already discussed with you, and seems obvious to me that you'll be strongly against anything that is related to Bodo. Including this case where Bodo can benefit from this, but this is clearly independent of any specific use case.

In any case, thanks for not blocking it if everyone else is happy to get this merged.

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The only bodo things I’ve opposed have been engine keywords in places they aren’t needed.

@datapythonista
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The only bodo things I’ve opposed have been engine keywords in places they aren’t needed.

You didn't oppose adding the engine keyword to apply. That was done by Thomas. You opposed making it more generic, so not only numba would benefit from it.

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Good clarification. I opposed there the same thing I oppose here, and for the same correct reasons.

@datapythonista
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Not sure if it makes sense to iterate much longer, but just a last comment on why I'm not convinced about your reasons (stated in this comment #61642 (comment)). And I continue to think being strongly opposed to this is based on other less objective reasons.

No users have asked for this

This is true for lots of things, in particular for work like this one, where one of the main motivations is make our CI easier, by being able to move code tricky to test to separate packages in a transparent way to users.

When a library such as xarray or fastparquet is not install, we silently stop testing the connector. It happened in the past (several years ago) that we spent weeks not testing IO connectors. The way we implement IO in pandas is wrong. Having the IO just outside of pandas is an option as you say. But we aren't removing read_sas, read_spss, read_clipboard, read_xarray from our API. This PR allows a better architecture without having to remove those and cause backward compatibility issues. In particular, this PR, followed up by related work, would reduce the maintenance of pandas, as IO code could live elsewhere. It would avoid the import_or_skip use which can easily lead to stop testing code in a silent way. It would simplify our dependendencies and its resolutions.

And of course, it would also allow to add new IO connectors at literally no cost for pandas. Polars and DuckDB have the fastest CSV readers. Should we add them as engines to pandas? Yes if we thinl about making read_csv faster. But probably not, if we need to add Polars and DuckDB as optional dependencies, maintain the wrappers among them... What's proposed in this PR immediately solves this at a minimal cost.

All downsides, no upsides

Exactly the opposite. I personally think you are repeatedly ignoring the upsides. I know you say that we can do the same without a pandas interface. But for good or for bad this is how pandas is designed. We could get rid of pandas.read_xarray, or pandas.read_clibpboard. You tried with the latter but it's not happening. So, saying we can just have pandas_clipboard.read_clipboard is not realistic.

this complicates the API

I disagree. This was true for PDEP-9, but not here. The API is the same. If users have fastparquet installed they will be able to use the engine, otherwise they won't and will get an error like now.

Users will have to learn that engines require packages to be installed, as it's the case now even if in a subtly different way. But the API is exactly the same.

more docs and more code and more tests increase burdens

The diff here is minimal, if you used this argument consistently, nothing would be ever added to pandas again.

What's more paradoxical is that if you consider this PR in the prespective that it'd allow moving connectors to other packages, then this is exactly the opposite. If we just move the fastparquet connector to their package, the burden already decreases. Or the clipboard, but I guess that would live in a new package and that's a bit trickier since it's not obvious who would maintain it. Not a big deal in my opinion, but that was a concern when PDEP-9 was discussed.

Users what we do and don't maintain

A valid point, but not sure how this PR is different than the status quo. So, if fastparquet is not installed, read_parquet with fastparquet engine won't work. If there is any problem in the data returned or an exception, it's very likely that it's a problem in fastparquet. Do users know it? I think they do in most cases actually. This PR probably helps in communicating, aa the fastparquet engine won't be mentioned in our API docs, but in the ecosystem, making ot clearer that they are using something not in pandas.

The main difference here is that now we do maintain wrappers that map our signature to the engine signature. Do users know that we maintain this tiny wrapper, and do they know when a problem with the connector is because the wrapper we maintain, or the external library? Probably not. So, probably once more this PR is helping solve your concern more than causing it.

You can of course hold any opinion about this you want. And in the case of apply I think some of your feedback was valuable and made the work there better. But I still have the feeling that you want to oppose this just because you don't like the way the agreement with Bodo works. And you are looking for reasons to your opposition, more than opposing this because of the reasons you presented. I can tell not only because the reasons don't seem factual, and don't seem important enough for strongly opposing it. But because of the double standards compared to other PRs. For example, you didn't have any concern when Thomas added engine to apply, then you presented all the concerns you could have there to me when I made what he implemented simpler and more generic. Or you don't have any opposition that I've seen to using entrypoints for acceasors. Which would be by far a better example of using the pandaa namespace for other's code than this engine system.

In any case, I genuinely appreciate your flexibility to be ok with this if there is broad support from other team members. I don't think I'll be able to make you like this, as in my mind your opposition is more ideological or emotional. But that flexibility and team work attitude is what allows the project to move forward. That's why I was more concerned about Irv's block, even if technically the disagreement is way smaller.

@WillAyd
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WillAyd commented Jul 3, 2025

Thanks all for some of the philosophical discussions around PR review. I know frustrating at times, but I think there are some positives in bringing those to light. Improving PR review is something we can as a team continue to work on, but at this point that is probably best to discuss in one of our core or governance team meetings to progress.

For the time being, I've given this PR some more thought and I'd be happy to throw my vote in as a +1. Yes, there are a few things I may not like or be unsure about, but stepping back I have a hard time envisioning this being very problematic. On the flip side, it helps at least one use case for now, and is done in a way that is generic to expand to others. If things really fall apart, it doesn't seem all that difficult to have to deprecate and move on :-)

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Dr-Irv commented Jul 3, 2025

So, the second thing we're talking about, is about blocking other people's PRs. I think blocking PRs is a useful tool we have, and I surely use it when needed. For example, if a PR is going to cause us future trouble, in our CI, with too much technical debt, with a poor experience for the users... I think it's great that we all can block PRs until the concerns are resolved. But for some reason, you seem to be abusing blocking PRs recently (at least in my opinion). If you agree with my comments about this PR above, you are literally not letting this PR be merged until I implement your (in my opinion) very opinionated and not very important comments of removing a release note that as I told you will be updated later. And to add an explanation about how to also add entry points with the legacy setup.py. If you share those as suggestions, I appreciate them, as I think it's good feedback. If other people agree with you, I'll be happy to update the PR with them. But if you block a PR for such trivial topics, it feels like you're making pandas your personal project, and that no work in pandas will be possible unless it follows your personal preferences. If that's the case, and pandas is happy with this sort of behavior, I surely don't want to continue contributing to it.

And this already happened recently in the df.select("col1", "col2"), which I think it's the same exact case.

I'm not sure what happened here to make you think I was "blocking" the PR. I did NOTHING proactively to make the PR blocked except I made some comments that I'd like you to address.

What I think has happened is that GitHub is now blocking PR's until all conversations are resolved. (This is something that I've seen with Gitlab on a customer project). So in this case, there were 3 conversations where I made the last comment - you can respond to those comments, and if I'm fine to move on from them, I can resolve the comments, and I think then the PR will become unblocked. Now I'm not sure what to do if you reopen this PR and others want to move it forward, and I don't resolve those conversations, as I will be disconnected for the next 2 weeks.

In the case of the select() PR, the typing you wanted to do was incorrect. And since the typing gets also reflected in pandas-stubs that I maintain, I think it is appropriate for me to ask you to get the typing declarations to be correct. But again, I did nothing to proactively block the PR. It appears blocked because of how GitHub is doing things.

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[Will] it helps at least one use case for now

Which one is that? I seriously would love to see a single use case where bodo.to_iceberg(df) isn't fully functional, clearer as to what's being called, clearer as to who is responsible for maintaining it, ... Is it really "save a few keystrokes for users who are pathologically addicted to method chaining"?

[Me] No users have asked for this

[Marc] This is true for lots of things, in particular for work like this one, where one of the main motivations is make our CI easier

As long as we're not-believing each other, I don't believe that this is one of the main motivations. If anything, it'll just mean that we'll be asked to add testing the bodo engine to our CI and further complicate things.

As I said before, if you want to move a reader/writer out of pandas, just open an issue about that explicitly.

[Me] this complicates the API

[Marc] I disagre

It adds a keyword to one method and suggests you're going to follow up by adding a keyword to a bunch more methods. And options for that keyword to methods that already have it. Yes, that is API complication.

Polars and DuckDB have the fastest CSV readers. Should we add them as engines to pandas?

I think that merits its own issue, but I don't anticipate having a problem with it as long as we are clear-eyed about the costs of maintaining that support.

The main difference here is that now we do maintain wrappers that map our signature to the engine signature. Do users know that we maintain this tiny wrapper, and do they know when a problem with the connector is because the wrapper we maintain, or the external library? Probably not. So, probably once more this PR is helping solve your concern more than causing it.

They complain to us regardless. When we're the ones who maintain the wrapper, we are actually the correct people to complain to. Even when it turns out to be an upstream issue, by maintaining the wrapper we actively decided to take on that responsibility. This would not be the case for 3rd party engines.

For example, you didn't have any concern when Thomas added engine to apply

IIRC we maintain the wrapper around numba, just like we do for the groupby.apply numba paths (which I paid more attention to). If I'm wrong on that and it'll make you feel better, I'll happily post some comments there about why it should be deprecated in favor of explicitly-3rd-party solution. And FWIW I am consistent about wanting to get rid of the engine keyword xref #53239.

Or you don't have any opposition that I've seen to using entrypoints for acceasors

Honestly not wild about that, but AFAICT 3rd party accessors are mostly used for in-house or personal use cases, as opposed to libraries (maybe geopandas?) so se la vie.

@datapythonista
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Thanks for the comment @Dr-Irv. It's my understanding that the convention is that when you review and set the flag "Requested changes" that's a block. At least to me, I don't think that PR is mergeable, and GitHub will also disable the merge button (it becomes red and you need an extra check box). For things that are not a blocker, I add the comments and review as a "Comment". That would in general also require that the reviewer to have a second look before merging, but at least to me not in the same way, if comments are addressed or answered, in general it's fine. If you don't follow this same procedure, that can be where the misunderstanding comes from, and maybe it'd be worth to make sure we're all in the same page. Maybe it's me who has been doing things differently.

Sorry @jbrockmendel, I guess I misunderstood, and it's just that we have exact opposite views on how pandas should play with other packages. To me pandas is too big and would benefit from "plugins" in many places, and you are more into monorepos, or not sure how to describe wanting to have everything in pandas. If that's the issue, we'll surely have disagreements in most of what I do. From the work on the plotting plugins, to the UDF executors, to third-party IO, most of what I do in pandas that is not maintenance is this sort of divide and conquer work. I guess there is no easy solution for it.

I'm not too bothered of a bodo writer being written as bodo.to_iceberg. As you say, it's functionally the same. I'm bothered that we don't then use pyarrow.read_parquet, xarray.to_pandas... As you suggested, I could open issues for those, and I guess I'd get your support there, but I'm sure there won't be consensus. I'll leave that battle to someone else, the approach I want to see in pandas is the one in this PR or PDEP-9.

And I do agree that adding engine is a change in the API. If done consistently everywhere seems like a small change to me, and users are already familiar with if they used read_csv or read_parquet. But it does introduce a change to the API, you are right with that.

@datapythonista datapythonista reopened this Jul 3, 2025
@WillAyd WillAyd dismissed Dr-Irv’s stale review July 3, 2025 16:10

Dismissing as this feedback is not meant to be a blocker, and the requestor is going on vacation. Confirmed by @Dr-Irv on Slack

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