Windows11安装LangChain遇multidict构建错误：需Visual C++14.0+

问题概述 #

在Windows 11系统、Python 3.12环境下执行pip install langchain安装LangChain，多数依赖包可正常安装，但构建multidict包时失败，抛出subprocess-exited-with-error错误，核心提示为Microsoft Visual C++ 14.0 or greater is required。用户已安装MS Visual Studio C++ 2015 Redistributable，但pip未识别该组件，导致安装中断，完整报错日志如下：

Building wheel for multidict (pyproject.toml) ... error
  error: subprocess-exited-with-error

  × Building wheel for multidict (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [74 lines of output]
      *********************
      * Accelerated build *
      *********************
      running bdist_wheel
      running build
      running build_py
      creating build
      creating build\lib.win-amd64-cpython-312
      creating build\lib.win-amd64-cpython-312\multidict
      copying multidict\_abc.py -> build\lib.win-amd64-cpython-312\multidict
      copying multidict\_compat.py -> build\lib.win-amd64-cpython-312\multidict
      copying multidict\_multidict_base.py -> build\lib.win-amd64-cpython-312\multidict
      copying multidict\_multidict_py.py -> build\lib.win-amd64-cpython-312\multidict
      copying multidict\__init__.py -> build\lib.win-amd64-cpython-312\multidict
      running egg_info
      writing multidict.egg-info\PKG-INFO
      writing dependency_links to multidict.egg-info\dependency_links.txt
      writing top-level names to multidict.egg-info\top_level.txt
      reading manifest file 'multidict.egg-info\SOURCES.txt'
      reading manifest template 'MANIFEST.in'
      warning: no previously-included files matching '*.pyc' found anywhere in distribution
      warning: no previously-included files found matching 'multidict\_multidict.html'
      warning: no previously-included files found matching 'multidict\*.so'
      warning: no previously-included files found matching 'multidict\*.pyd'
      warning: no previously-included files found matching 'multidict\*.pyd'
      no previously-included directories found matching 'docs\_build'
      adding license file 'LICENSE'
      writing manifest file 'multidict.egg-info\SOURCES.txt'
      C:\Users\demotextxxx\AppData\Local\Temp\pip-build-env-b2hbx2bu\overlay\Lib\site-packages\setuptools\command\build_py.py:207: _Warning: Package 'multidict._multilib' is absent from the `packages` configuration.
      !!

              ********************************************************************************
              ############################
              # Package would be ignored #
              ############################
              Python recognizes 'multidict._multilib' as an importable package[^1],
              but it is absent from setuptools' `packages` configuration.

              This leads to an ambiguous overall configuration. If you want to distribute this
              package, please make sure that 'multidict._multilib' is explicitly added
              to the `packages` configuration field.

              Alternatively, you can also rely on setuptools' discovery methods
              (for example by using `find_namespace_packages(...)`/`find_namespace:`
              instead of `find_packages(...)`/`find:`).

              You can read more about "package discovery" on setuptools documentation page:

              - https://setuptools.pypa.io/en/latest/userguide/package_discovery.html

              If you don't want 'multidict._multilib' to be distributed and are
              already explicitly excluding 'multidict._multilib' via
              `find_namespace_packages(...)/find_namespace` or `find_packages(...)/find`,
              you can try to use `exclude_package_data`, or `include-package-data=False` in
              combination with a more fine grained `package-data` configuration.

              You can read more about "package data files" on setuptools documentation page:

              - https://setuptools.pypa.io/en/latest/userguide/datafiles.html


              [^1]: For Python, any directory (with suitable naming) can be imported,
                    even if it does not contain any `.py` files.
                    On the other hand, currently there is no concept of package data
                    directory, all directories are treated like packages.
              ********************************************************************************

      !!
        check.warn(importable)
      copying multidict\__init__.pyi -> build\lib.win-amd64-cpython-312\multidict
      copying multidict\py.typed -> build\lib.win-amd64-cpython-312\multidict
      running build_ext
      building 'multidict._multidict' extension
      error: Microsoft Visual C++ 14.0 or greater is required. Get it with "Microsoft C++ Build Tools": https://visualstudio.microsoft.com/visual-cpp-build-tools/
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
  ERROR: Failed building wheel for multidict
Failed to build multidict
ERROR: Could not build wheels for multidict, which is required to install pyproject.toml-based projects

解决办法 #

• 安装完整的Microsoft C++ Build Tools
  Visual C++ Redistributable仅为运行时库，无法满足编译扩展包的需求。需下载并安装Microsoft C++ Build Tools，安装时务必勾选「Desktop development with C++」组件，确保包含MSVC v142及以上版本的工具集、对应的Windows SDK等核心编译组件。安装完成后重启终端，重新执行pip install langchain。

• 直接安装预编译的multidict wheel包
  若不想安装构建工具，可直接使用预编译的二进制包：

  pip install --force-reinstall multidict --only-binary :all:
  

  完成后再次执行pip install langchain即可。

• 验证环境变量配置
  安装构建工具后，检查系统环境变量是否包含MSVC的路径（通常为C:\Program Files (x86)\Microsoft Visual Studio\<版本>\BuildTools\VC\Tools\MSVC\<版本号>\bin\Hostx64\x64），若未添加则手动加入，重启终端后重试安装。

内容的提问来源于stack exchange，提问作者Chandan