Missing cblas.dll in the Windows pypi wheel

[rozyczko]

Problem

diffpy.pdffit2 installed on windows (any Python) can't be run, since gsl-25.dll requires libcblas.dll to run.

1. create new python environment
2. pip install diffpy.pdffit2
3. run python -c "import diffpy.pdffit2"
4. observe import error

Looking at gsl-25.dll included in the wheel, we see dependency on libcblas.dll

Proposed solution

Add libcblas.dll (and any potential dependencies of it) to the wheel. This can be taken from the conda-forge distribution of libcblas

[sbillinge]

@Tieqiong this seems familiar, but please could you take a look?

[Tieqiong]

@sbillinge Yes will test and fix this.

[stevenhua0320]

@sbillinge Have we fixed this? Since I don't have laptop with Windows at hand, I cannot test it right away.

[sbillinge]

I will check. Please give me a minute

[sbillinge]

I can confirm that everything works when installing from conda-forge, however, when installing directly from pip we are getting this import error:

[stevenhua0320]

I can confirm that everything works when installing from conda-forge, however, when installing directly from pip we are getting this import error:

I'm looking into this and checking where it breaks the import.

[sbillinge]

Thanks. If you need help, please reach out to @Tieqiong

[stevenhua0320]

@Tieqiong could you help to look at why now we cannot import the pdffit2 directly by pip install it?

[sbillinge]

@stevenhua0320 I checked and this is still not working on our latest vesrsion of the code.

Here are steps to fix this per chatgpt:
Here’s the practical, step-by-step way to bundle a C library DLL (e.g., libcblas.dll) inside a Python wheel so users don’t have to install it separately — exactly what the advice you received is referring to.

---

✅ How Python wheels handle DLLs on Windows

Wheels can contain native shared libraries (.dll, .so, .dylib) inside the wheel.
At runtime, Python loads them automatically as long as they are placed in the correct location in the wheel.

For Windows, the correct place is usually:

mypackage/
    ___init__.py
    your_python_modules.py
    libcblas.dll     ← place DLL directly inside your package

Python will automatically search for DLLs located next to your extension modules or package code.

---

✅ How to include libcblas.dll in your wheel

Step 1 — Get libcblas.dll from conda-forge

Install the conda-forge package:

micromamba install -c conda-forge libcblas

Then locate the DLL:

<micromamba env>/Library/bin/libcblas.dll

Copy that file into your Python package directory, e.g.:

yourpackage/
    __init__.py
    ...
    lib/
        libcblas.dll

Or put it at the top level of the package:

yourpackage/libcblas.dll

Both layouts work, but top-level inside the package is simplest.

---

✅ Step 2 — Add the DLL to your wheel using package_data

If you're using pyproject.toml with setuptools, add something like:

[tool.setuptools.package-data]
yourpackage = ["libcblas.dll"]

Or if you put it into a lib/ folder:

[tool.setuptools.package-data]
yourpackage = ["lib/*.dll"]

If you're using setup.py, use package_data:

from setuptools import setup

setup(
    name="yourpackage",
    ...
    package_data={
        "yourpackage": ["libcblas.dll"],   # Or "lib/*.dll"
    },
    include_package_data=True,
)

---

✅ Step 3 — Verify that the wheel contains the DLL

Build your wheel:

python -m build

List the wheel contents:

unzip -l dist/yourpackage-*.whl

You should see:

yourpackage/libcblas.dll

---

✅ Step 4 — Ensure Python can load the DLL

Put this in your __init__.py or in your module that loads C code:

import os
import sys

# Add package directory to PATH so Windows can find the DLL
this_dir = os.path.dirname(__file__)
os.add_dll_directory(this_dir)

Python 3.8+ needs this on Windows because DLL loading rules changed.

If your DLL is in a subfolder:

os.add_dll_directory(os.path.join(this_dir, "lib"))

---

⭐ Extra Notes

1. Bundling dependencies of dependencies

libcblas.dll may depend on:

• libgfortran
• libgcc
• msvcp???.dll
• etc.

You can discover dependencies using:

objdump -p libcblas.dll  # On Linux

or:

dumpbin /DEPENDENTS libcblas.dll

Most conda-forge DLLs depend on other conda-forge DLLs — you will need to include those as well unless they are Windows system DLLs.

---

[stevenhua0320]

@sbillinge I have checked that libcblas file would have different file format. For MacOS (since I'm in Mac), the file ends with .dylib, which is not the file with format dll. I think dll file is supported on windows only. So, to get the file I think I need to manually download the dll file from conda-forge?
From my point, it is safer to do it for a person with a windows system as it can directly download from conda-forge with correct dll format and can build the package locally to see whether there's something wrong in the build of the package.

[sbillinge]

Sounds good. Please work directly with someone who has windows.

[ycexiao]

libcblas.dll from conda-forge doesn't work, and libgslcblas-0.dll from mingw64 suggested by ChatGPT also doesn't work. I'm not sure why, but I tried to use the file downloaded from mingw64, renaming it to libcblas.dll, and it worked.

1. Install mingw64, run pacman -Syu, pacman -S mingw-w64-x86_64-gsl
2. Copy libgslcbls-0.dll into diffpy.pdffit2/src/diffpy/pdffit2
3. Rename libgslcbls-0.dll to libcbls.dll.
4. Modify setup.py, add libgslcbls.dll as package_data

setup_args = dict(
    ext_modules=[],
    cmdclass={"build_ext": CustomBuildExt},
    package_data={"diffpy.pdffit2": ["libcblas.dll"]},  # added
)

5. Run python -m build

6. pip install the whl in test-pdffit

7. run python -c "import diffpy.pdffit2; print(diffpy.pdffit2.__version__)"

I think it is working now. @stevenhua0320, do you need the whl file I built in my local machine?

[stevenhua0320]

Thanks @ycexiao ! could you create a PR for the edits you created and also send the wheel file to both me and @sbillinge so that we can test it out?

[ycexiao]

I think the edits I made only make sense for windows. Should these be included in our source code?