[python-package] Cannot import lightgbm after installation on windows with `uv`, lib_lightgbm.dll not found

[diego-pm]

Description

Cannot import lightgbm after installing it with uv. I am aware uv might not be supported, but I also tried to install it with pip inside the virtual environment, and get the same error.

The error I get when trying to import the package is the following:

FileNotFoundError                         Traceback (most recent call last)
Cell In[2], line 9
      6 
      7 
----> 9 import lightgbm as lgb
     10 
     11 

File c:\Users\project\.venv\Lib\site-packages\lightgbm\__init__.py:11
      7 from pathlib import Path
      9 # .basic is intentionally loaded as early as possible, to dlopen() lib_lightgbm.{dll,dylib,so}
     10 # and its dependencies as early as possible
---> 11 from .basic import Booster, Dataset, Sequence, register_logger
     12 from .callback import EarlyStopException, early_stopping, log_evaluation, record_evaluation, reset_parameter
     13 from .engine import CVBooster, cv, train

File c:\Users\project\.venv\Lib\site-packages\lightgbm\basic.py:9
      2 """Wrapper for C API of LightGBM."""
      4 # This import causes lib_lightgbm.{dll,dylib,so} to be loaded.
      5 # It's intentionally done here, as early as possible, to avoid issues like
      6 # "libgomp.so.1: cannot allocate memory in static TLS block" on aarch64 Linux.
      7 #
      8 # For details, see the "cannot allocate memory in static TLS block" entry in docs/FAQ.rst.
----> 9 from .libpath import _LIB  # isort: skip
     11 import abc
     12 import ctypes

File c:\Users\project\.venv\Lib\site-packages\lightgbm\libpath.py:49
     47     _LIB = Mock(ctypes.CDLL)  # type: ignore
     48 else:
---> 49     _LIB = ctypes.cdll.LoadLibrary(_find_lib_path()[0])

File ~\AppData\Roaming\uv\python\cpython-3.13.2-windows-x86_64-none\Lib\ctypes\__init__.py:471, in LibraryLoader.LoadLibrary(self, name)
    470 def LoadLibrary(self, name):
--> 471     return self._dlltype(name)

File ~\AppData\Roaming\uv\python\cpython-3.13.2-windows-x86_64-none\Lib\ctypes\__init__.py:390, in CDLL.__init__(self, name, mode, handle, use_errno, use_last_error, winmode)
    387 self._FuncPtr = _FuncPtr
    389 if handle is None:
--> 390     self._handle = _dlopen(self._name, mode)
    391 else:
    392     self._handle = handle

FileNotFoundError: Could not find module 'c:\Users\project\.venv\Lib\site-packages\lightgbm\bin\lib_lightgbm.dll' (or one of its dependencies). Try using the full path with constructor syntax.

Reproducible example

uv add lightgbm

import lightgbm

Environment info

LightGBM version or commit hash: 4.6.0

Command(s) you used to install LightGBM

uv add lightgbm
# alternatively
python -m pip install lightgbm==4.6.0

Windows 10
Powershell 5.1

Additional Comments

Found related issues: #6079, #5335, #5261, stack overflow question

But I haven't been able to fix this, these issues seem to give solutions for building the library from source.

[diego-pm]

I think I fixed the problem, sorry for opening the issue. It works now after installing Microsoft C++ Build Tools.

[jameslamb]

Thanks for using LightGBM and for taking the time to report this.

I'm glad that building from source worked for you, but that really should not be necessary. I'd like to understand why uv didn't choose to install the pre-built wheels we publish for Windows.

lightgbm-4.6.0-py3-none-win_amd64.whl

ref: https://pypi.org/project/lightgbm/#files

What does this Python code print for you?

import platform
import sys
print(platform.platform())
print(platform.win32_ver())
print(sys.version)

Could you share the logs from running python -m pip install lightgbm==4.6.0 and/org uv add lightgbm?

[diego-pm]

I forgot to mention that the binary lib_lightgbm.dll did exist in the path specified by the error message, but I still got the error. And by installing Microsoft C++ build tools, the error disappeared without having to build the package from source (I think).

What does this Python code print for you?

import platform
import sys
print(platform.platform())
print(platform.win32_ver())
print(sys.version)

Windows-10-10.0.19045-SP0
('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
3.13.2 (main, Feb 12 2025, 14:49:53) [MSC v.1942 64 bit (AMD64)]

Could you share the logs from running python -m pip install lightgbm==4.6.0 and/org uv add lightgbm?

after running python -m pip install lightgbm==4.6.0, I get:

Collecting lightgbm==4.6.0
  Using cached lightgbm-4.6.0-py3-none-win_amd64.whl.metadata (17 kB)
Requirement already satisfied: numpy>=1.17.0 in c:\users\project\.venv\lib\site-packages (from lightgbm==4.6.0) (2.2.6)
Requirement already satisfied: scipy in c:\users\project\.venv\lib\site-packages (from lightgbm==4.6.0) (1.15.3)
Using cached lightgbm-4.6.0-py3-none-win_amd64.whl (1.5 MB)
Installing collected packages: lightgbm
Successfully installed lightgbm-4.6.0

after running uv add -v lightgbm I get:

uv : DEBUG uv 0.7.12 (dc3fd4647 2025-06-06) At line:1 char:1 + uv add -v lightgbm > logs.txt 2>&1 + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : NotSpecified: (DEBUG uv 0.7.12 (dc3fd4647 2025-06-06):String) [], RemoteException + FullyQualifiedErrorId : NativeCommandError

DEBUG Found project root: C:\Users\project
DEBUG No workspace root found, using project root
DEBUG Acquired lock for C:\Users\project
DEBUG Reading Python requests from version file at C:\Users\project\.python-version
DEBUG Using Python request 3.13 from version file at .python-version
DEBUG Checking for Python environment at .venv
DEBUG The project environment's Python version satisfies the request: Python 3.13
DEBUG Released lock at C:\Users\user\AppData\Local\Temp\uv-c3da7c6a15b50a0d.lock
DEBUG Acquired lock for .venv
DEBUG Using request timeout of 30s
DEBUG Found static pyproject.toml for: project @ file:///C:/Users/project
DEBUG No workspace root found, using project root
DEBUG Ignoring existing lockfile due to mismatched requirements for: project==0.1.0
Requested: {Requirement { name: PackageName("lightgbm"), extras: [], groups: [], marker: true, source: Registry { specifier: VersionSpecifiers([]), index: None, conflict: None }, origin: None }}
Existing: {}
DEBUG Solving with installed Python version: 3.13.2
DEBUG Solving with target Python version: >=3.13
DEBUG Adding direct dependency: project*
DEBUG Adding direct dependency: project:dev*
DEBUG Searching for a compatible version of project @ file:///C:/Users/project ()
DEBUG Adding direct dependency: lightgbm
DEBUG Searching for a compatible version of project @ file:///C:/Users/project ()
DEBUG Adding direct dependency: project:dev==0.1.0
DEBUG Searching for a compatible version of project @ file:///C:/Users/project (==0.1.0)
DEBUG Acquired lock for C:\Users\user\.uv_cache\simple-v16\pypi\lightgbm.lock
DEBUG No cache entry for: https://pypi.org/simple/lightgbm/
DEBUG Released lock at C:\Users\user\.uv_cache\simple-v16\pypi\lightgbm.lock
DEBUG Searching for a compatible version of lightgbm ()
DEBUG Selecting: lightgbm==4.6.0 [compatible] (lightgbm-4.6.0-py3-none-macosx_10_15_x86_64.whl)
DEBUG Acquired lock for C:\Users\user\.uv_cache\wheels-v5\pypi\lightgbm\lightgbm-4.6.0-py3-none-macosx_10_15_x86_64.lock
DEBUG No cache entry for: https://files.pythonhosted.org/packages/f2/75/cffc9962cca296bc5536896b7e65b4a7cdeb8db208e71b9c0133c08f8f7e/lightgbm-4.6.0-py3-none-macosx_10_15_x86_64.whl.metadata
DEBUG Released lock at C:\Users\user\.uv_cache\wheels-v5\pypi\lightgbm\lightgbm-4.6.0-py3-none-macosx_10_15_x86_64.lock
DEBUG Adding transitive dependency for lightgbm==4.6.0: numpy>=1.17.0
DEBUG Adding transitive dependency for lightgbm==4.6.0: scipy*
DEBUG Acquired lock for C:\Users\user\.uv_cache\simple-v16\pypi\numpy.lock
DEBUG Acquired lock for C:\Users\user\.uv_cache\simple-v16\pypi\scipy.lock
DEBUG No cache entry for: https://pypi.org/simple/numpy/
DEBUG No cache entry for: https://pypi.org/simple/scipy/
DEBUG Released lock at C:\Users\user\.uv_cache\simple-v16\pypi\scipy.lock
DEBUG Acquired lock for C:\Users\user\.uv_cache\wheels-v5\pypi\scipy\scipy-1.15.3-cp313-cp313-macosx_10_13_x86_64.lock
DEBUG No cache entry for: https://files.pythonhosted.org/packages/73/18/ec27848c9baae6e0d6573eda6e01a602e5649ee72c27c3a8aad673ebecfd/scipy-1.15.3-cp313-cp313-macosx_10_13_x86_64.whl.metadata
WARN Skipping file for numpy: numpy-1.0.1.dev3460.win32-py2.4.exe
WARN Skipping file for numpy: numpy-1.3.0.win32-py2.5.exe
WARN Skipping file for numpy: numpy-1.5.0.win32-py2.6.exe
WARN Skipping file for numpy: numpy-1.5.1.win32-py2.5-nosse.exe
WARN Skipping file for numpy: numpy-1.5.1.win32-py2.6-nosse.exe
WARN Skipping file for numpy: numpy-1.5.1.win32-py2.7-nosse.exe
WARN Skipping file for numpy: numpy-1.5.1.win32-py3.1-nosse.exe
WARN Skipping file for numpy: numpy-1.6.0.win32-py2.5.exe
WARN Skipping file for numpy: numpy-1.6.0.win32-py2.6.exe
WARN Skipping file for numpy: numpy-1.6.0.win32-py2.7.exe
WARN Skipping file for numpy: numpy-1.6.0.win32-py3.1.exe
WARN Skipping file for numpy: numpy-1.6.0.win32-py3.2.exe
WARN Skipping file for numpy: numpy-1.6.1.win32-py2.5.exe
WARN Skipping file for numpy: numpy-1.6.1.win32-py2.6.exe
WARN Skipping file for numpy: numpy-1.6.1.win32-py2.7.exe
WARN Skipping file for numpy: numpy-1.6.1.win32-py3.1.exe
WARN Skipping file for numpy: numpy-1.6.1.win32-py3.2.exe
WARN Skipping file for numpy: numpy-1.6.2.win32-py2.5.exe
WARN Skipping file for numpy: numpy-1.6.2.win32-py2.6.exe
WARN Skipping file for numpy: numpy-1.6.2.win32-py2.7.exe
WARN Skipping file for numpy: numpy-1.6.2.win32-py3.1.exe
WARN Skipping file for numpy: numpy-1.6.2.win32-py3.2.exe
WARN Skipping file for numpy: numpy-1.7.0.win32-py2.5.exe
WARN Skipping file for numpy: numpy-1.7.0.win32-py2.6.exe
WARN Skipping file for numpy: numpy-1.7.0.win32-py2.7.exe
WARN Skipping file for numpy: numpy-1.7.0.win32-py3.1.exe
WARN Skipping file for numpy: numpy-1.7.0.win32-py3.2.exe
WARN Skipping file for numpy: numpy-1.7.0.win32-py3.3.exe
WARN Skipping file for numpy: numpy-1.7.1.win32-py2.5.exe
WARN Skipping file for numpy: numpy-1.7.1.win32-py2.6.exe
WARN Skipping file for numpy: numpy-1.7.1.win32-py2.7.exe
WARN Skipping file for numpy: numpy-1.7.1.win32-py3.1.exe
WARN Skipping file for numpy: numpy-1.7.1.win32-py3.2.exe
WARN Skipping file for numpy: numpy-1.7.1.win32-py3.3.exe
DEBUG Released lock at C:\Users\user\.uv_cache\simple-v16\pypi\numpy.lock
DEBUG Searching for a compatible version of numpy (>=1.17.0)
DEBUG Selecting: numpy==2.3.0 [compatible] (numpy-2.3.0-cp313-cp313-macosx_10_13_x86_64.whl)
DEBUG Acquired lock for C:\Users\user\.uv_cache\wheels-v5\pypi\numpy\numpy-2.3.0-cp313-cp313-macosx_10_13_x86_64.lock
DEBUG No cache entry for: https://files.pythonhosted.org/packages/73/fc/1d67f751fd4dbafc5780244fe699bc4084268bad44b7c5deb0492473127b/numpy-2.3.0-cp313-cp313-macosx_10_13_x86_64.whl.metadata
DEBUG Released lock at C:\Users\user\.uv_cache\wheels-v5\pypi\scipy\scipy-1.15.3-cp313-cp313-macosx_10_13_x86_64.lock
DEBUG Released lock at C:\Users\user\.uv_cache\wheels-v5\pypi\numpy\numpy-2.3.0-cp313-cp313-macosx_10_13_x86_64.lock
DEBUG Searching for a compatible version of scipy ()
DEBUG Selecting: scipy==1.15.3 [compatible] (scipy-1.15.3-cp313-cp313-macosx_10_13_x86_64.whl)
DEBUG Adding transitive dependency for scipy==1.15.3: numpy>=1.23.5, <2.5
DEBUG Tried 4 versions: project 1, lightgbm 1, numpy 1, scipy 1
DEBUG all marker environments resolution took 0.431s
Resolved 4 packages in 443ms
DEBUG Using request timeout of 30s
DEBUG Found static pyproject.toml for: project @ file:///C:/Users/project
DEBUG No workspace root found, using project root
DEBUG Ignoring existing lockfile due to mismatched requirements for: project==0.1.0
Requested: {Requirement { name: PackageName("lightgbm"), extras: [], groups: [], marker: true, source: Registry { specifier: VersionSpecifiers([VersionSpecifier { operator: GreaterThanEqual, version: "4.6.0" }]),
index: None, conflict: None }, origin: None }}
Existing: {Requirement { name: PackageName("lightgbm"), extras: [], groups: [], marker: true, source: Registry { specifier: VersionSpecifiers([]), index: None, conflict: None }, origin: None }}
DEBUG Solving with installed Python version: 3.13.2
DEBUG Solving with target Python version: >=3.13
DEBUG Adding direct dependency: project
DEBUG Adding direct dependency: project:dev*
DEBUG Searching for a compatible version of project @ file:///C:/Users/project ()
DEBUG Adding direct dependency: lightgbm>=4.6.0
DEBUG Searching for a compatible version of project @ file:///C:/Users/project ()
DEBUG Adding direct dependency: project:dev==0.1.0
DEBUG Searching for a compatible version of project @ file:///C:/Users/project (==0.1.0)
DEBUG Searching for a compatible version of lightgbm (>=4.6.0)
DEBUG Selecting: lightgbm==4.6.0 [preference] (lightgbm-4.6.0-py3-none-macosx_10_15_x86_64.whl)
DEBUG Adding transitive dependency for lightgbm==4.6.0: numpy>=1.17.0
DEBUG Adding transitive dependency for lightgbm==4.6.0: scipy*
DEBUG Searching for a compatible version of numpy (>=1.17.0)
DEBUG Selecting: numpy==2.3.0 [preference] (numpy-2.3.0-cp313-cp313-macosx_10_13_x86_64.whl)
DEBUG Searching for a compatible version of scipy (*)
DEBUG Selecting: scipy==1.15.3 [preference] (scipy-1.15.3-cp313-cp313-macosx_10_13_x86_64.whl)
DEBUG Adding transitive dependency for scipy==1.15.3: numpy>=1.23.5, <2.5
DEBUG Tried 4 versions: project 1, lightgbm 1, numpy 1, scipy 1
DEBUG all marker environments resolution took 0.001s
DEBUG Using request timeout of 30s
DEBUG Identified uncached distribution: lightgbm==4.6.0
DEBUG Identified uncached distribution: numpy==2.3.0
DEBUG Identified uncached distribution: scipy==1.15.3
DEBUG Acquired lock for C:\Users\user\.uv_cache\wheels-v5\pypi\scipy\scipy-1.15.3-cp313-cp313-win_amd64.lock
DEBUG Acquired lock for C:\Users\user\.uv_cache\wheels-v5\pypi\numpy\numpy-2.3.0-cp313-cp313-win_amd64.lock
DEBUG Acquired lock for C:\Users\user\.uv_cache\wheels-v5\pypi\lightgbm\lightgbm-4.6.0-py3-none-win_amd64.lock
DEBUG No cache entry for: https://files.pythonhosted.org/packages/5e/23/f8b28ca248bb629b9e08f877dd2965d1994e1674a03d67cd10c5246da248/lightgbm-4.6.0-py3-none-win_amd64.whl
DEBUG No cache entry for: https://files.pythonhosted.org/packages/08/60/61d60cf0dfc0bf15381eaef46366ebc0c1a787856d1db0c80b006092af84/numpy-2.3.0-cp313-cp313-win_amd64.whl
DEBUG No cache entry for: https://files.pythonhosted.org/packages/87/2e/892ad2862ba54f084ffe8cc4a22667eaf9c2bcec6d2bff1d15713c6c0703/scipy-1.15.3-cp313-cp313-win_amd64.whl
Downloading lightgbm (1.4MiB)
Downloading scipy (39.1MiB)
Downloading numpy (12.1MiB)
Downloading lightgbm
DEBUG Released lock at C:\Users\user\.uv_cache\wheels-v5\pypi\lightgbm\lightgbm-4.6.0-py3-none-win_amd64.lock
Downloading numpy
DEBUG Released lock at C:\Users\user\.uv_cache\wheels-v5\pypi\numpy\numpy-2.3.0-cp313-cp313-win_amd64.lock
Downloading scipy
DEBUG Released lock at C:\Users\user\.uv_cache\wheels-v5\pypi\scipy\scipy-1.15.3-cp313-cp313-win_amd64.lock
Prepared 3 packages in 3.90s
Installed 3 packages in 827ms

• lightgbm==4.6.0
• numpy==2.3.0
• scipy==1.15.3
  DEBUG Released lock at C:\Users\project\.venv\.lock

[jameslamb]

I forgot to mention that the binary lib_lightgbm.dll did exist in the path specified by the error message, but I still got the error. And by installing Microsoft C++ build tools, the error disappeared

Oh that is VERY interesting!

From the logs you shared, it does look like you got a wheel as expected and nothing was built from source.

Given these two things, now I think it's more like "some DLL required by lib_lightgbm.dll wasn't present on your system, and installing the Microsoft C++ build tools provided it".

Since you've now installed those tools, you should have dumpbin installed (docs).

Could you try something like this, and share the outputs here?

dumpbin /dependents "c:\Users\project\.venv\Lib\site-packages\lightgbm\bin\lib_lightgbm.dll"

I found that tool helpful before (#4464 (comment)).

I can also try to reproduce this on a Windows system I have access to, when time permits.

Thank you for helping us to make this better for other Windows users, and very sorry for the inconvenience!

[diego-pm]

Thanks for your help!

Could you try something like this, and share the outputs here?

dumpbin /dependents "c:\Users\project.venv\Lib\site-packages\lightgbm\bin\lib_lightgbm.dll"

Microsoft (R) COFF/PE Dumper Version 14.44.35209.0
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file c:\Users\project\.venv\Lib\site-packages\lightgbm\bin\lib_lightgbm.dll

File Type: DLL

  Image has the following dependencies:

    CFGMGR32.dll
    api-ms-win-core-winrt-string-l1-1-0.dll
    api-ms-win-core-winrt-l1-1-0.dll
    KERNEL32.dll
    ole32.dll
    ADVAPI32.dll
    MSVCP140.dll
    VCOMP140.DLL
    WS2_32.dll
    IPHLPAPI.DLL
    VCRUNTIME140.dll
    VCRUNTIME140_1.dll
    api-ms-win-crt-runtime-l1-1-0.dll
    api-ms-win-crt-math-l1-1-0.dll
    api-ms-win-crt-heap-l1-1-0.dll
    api-ms-win-crt-stdio-l1-1-0.dll
    api-ms-win-crt-filesystem-l1-1-0.dll
    api-ms-win-crt-convert-l1-1-0.dll
    api-ms-win-crt-locale-l1-1-0.dll
    api-ms-win-crt-environment-l1-1-0.dll
    api-ms-win-crt-string-l1-1-0.dll

  Summary

       1B000 .data
       1C000 .pdata
       92000 .rdata
        4000 .reloc
        1000 .rsrc
      315000 .text