Use uv and derive as much as possible from the environment, if available by filmor · Pull Request #2652 · pythonnet/pythonnet · GitHub
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Use uv and derive as much as possible from the environment, if available #2652

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Merged
filmor merged 3 commits into from
Oct 25, 2025
Merged

Use uv and derive as much as possible from the environment, if available #2652

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8d8bf26
Use uv
filmor Nov 25, 2024
9e6ffba
Derive program name from venv if possible
filmor Oct 25, 2025
3a3abb9
Implement venv derivation
filmor Oct 25, 2025
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31 changes: 5 additions & 26 deletions .github/workflows/main.yml
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2 changes: 1 addition & 1 deletion src/runtime/Python.Runtime.csproj
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
<PropertyGroup>
<TargetFrameworks>netstandard2.0</TargetFrameworks>
<Platforms>AnyCPU</Platforms>
<LangVersion>10.0</LangVersion>
<LangVersion>10</LangVersion>
<RootNamespace>Python.Runtime</RootNamespace>
<AssemblyName>Python.Runtime</AssemblyName>
<Nullable>enable</Nullable>
Expand Down
43 changes: 19 additions & 24 deletions src/runtime/Runtime.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
using System.Text;
using System.Threading;
using System.Collections.Generic;
using System.IO;
using Python.Runtime.Native;
using System.Linq;
using static System.FormattableString;
Expand All @@ -18,40 +19,20 @@ namespace Python.Runtime
/// </summary>
public unsafe partial class Runtime
{
internal static PythonEnvironment PythonEnvironment = PythonEnvironment.FromEnv();

public static string? PythonDLL
{
get => _PythonDll;
set
{
if (_isInitialized)
throw new InvalidOperationException("This property must be set before runtime is initialized");
_PythonDll = value;
PythonEnvironment.LibPython = value;
}
}

static string? _PythonDll = GetDefaultDllName();
private static string? GetDefaultDllName()
{
string dll = Environment.GetEnvironmentVariable("PYTHONNET_PYDLL");
if (dll is not null) return dll;

string verString = Environment.GetEnvironmentVariable("PYTHONNET_PYVER");
if (!Version.TryParse(verString, out var version)) return null;

return GetDefaultDllName(version);
}

private static string GetDefaultDllName(Version version)
{
string prefix = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "" : "lib";
string suffix = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
? Invariant($"{version.Major}{version.Minor}")
: Invariant($"{version.Major}.{version.Minor}");
string ext = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? ".dll"
: RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ? ".dylib"
: ".so";
return prefix + "python" + suffix + ext;
}
static string? _PythonDll => PythonEnvironment.LibPython;

private static bool _isInitialized = false;
internal static bool IsInitialized => _isInitialized;
Expand Down Expand Up @@ -96,6 +77,18 @@ internal static int GetRun()
return runNumber;
}

static void EnsureProgramName()
{
if (!string.IsNullOrEmpty(PythonEngine.ProgramName))
return;

if (PythonEnvironment.IsValid)
{
PythonEngine.ProgramName = PythonEnvironment.ProgramName!;
return;
}
}

internal static bool HostedInPython;
internal static bool ProcessIsTerminating;

Expand All @@ -117,6 +110,8 @@ internal static void Initialize(bool initSigs = false)
);
if (!interpreterAlreadyInitialized)
{
EnsureProgramName();

Py_InitializeEx(initSigs ? 1 : 0);

NewRun();
Expand Down
188 changes: 188 additions & 0 deletions src/runtime/Util/PythonEnvironment.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,188 @@
using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using static System.FormattableString;

namespace Python.Runtime;


internal class PythonEnvironment
{
readonly static string PYDLL_ENV_VAR = "PYTHONNET_PYDLL";
readonly static string PYEXE_ENV_VAR = "PYTHONNET_PYEXE";
readonly static string PYNET_VENV_ENV_VAR = "PYTHONNET_VENV";
readonly static string VENV_ENV_VAR = "VIRTUAL_ENV";

public string? VenvPath { get; private set; }
public string? Home { get; private set; }
public Version? Version { get; private set; }
public string? ProgramName { get; set; }
public string? LibPython { get; set; }

public bool IsValid =>
!string.IsNullOrEmpty(ProgramName) && !string.IsNullOrEmpty(LibPython);


// TODO: Move the lib-guessing step to separate function, use together with
// PYTHONNET_PYEXE or a path lookup as last resort

// Initialize PythonEnvironment instance from environment variables.
//
// If PYTHONNET_PYEXE and PYTHONNET_PYDLL are set, these always have precedence.
// If PYTHONNET_VENV or VIRTUAL_ENV is set, we interpret the environment as a venv
// and set the ProgramName/LibPython accordingly. PYTHONNET_VENV takes precedence.
public static PythonEnvironment FromEnv()
{
var pydll = Environment.GetEnvironmentVariable(PYDLL_ENV_VAR);
var pydllSet = !string.IsNullOrEmpty(pydll);
var pyexe = Environment.GetEnvironmentVariable(PYEXE_ENV_VAR);
var pyexeSet = !string.IsNullOrEmpty(pyexe);
var pynetVenv = Environment.GetEnvironmentVariable(PYNET_VENV_ENV_VAR);
var pynetVenvSet = !string.IsNullOrEmpty(pynetVenv);
var venv = Environment.GetEnvironmentVariable(VENV_ENV_VAR);
var venvSet = !string.IsNullOrEmpty(venv);

PythonEnvironment? res = new();

if (pynetVenvSet)
res = FromVenv(pynetVenv) ?? res;
else if (venvSet)
res = FromVenv(venv) ?? res;

if (pyexeSet)
res.ProgramName = pyexe;

if (pydllSet)
res.LibPython = pydll;

return res;
}

public static PythonEnvironment? FromVenv(string path)
{
var env = new PythonEnvironment
{
VenvPath = path
};

string venvCfg = Path.Combine(path, "pyvenv.cfg");

if (!File.Exists(venvCfg))
return null;

var settings = TryParse(venvCfg);

if (!settings.ContainsKey("home"))
return null;

env.Home = settings["home"];
var pname = ProgramNameFromPath(path);
if (File.Exists(pname))
env.ProgramName = pname;

if (settings.TryGetValue("version", out string versionStr))
{
_ = Version.TryParse(versionStr, out Version versionObj);
env.Version = versionObj;
}
else if (settings.TryGetValue("version_info", out versionStr))
{
_ = Version.TryParse(versionStr, out Version versionObj);
env.Version = versionObj;
}

env.LibPython = FindLibPython(env.Home, env.Version);

return env;
}

private static Dictionary<string, string> TryParse(string venvCfg)
{
var settings = new Dictionary<string, string>();

string[] lines = File.ReadAllLines(venvCfg);

// The actually used format is really primitive: "<key> = <value>"
foreach (string line in lines)
{
var split = line.Split(new[] { '=' }, 2);

if (split.Length != 2)
continue;

settings[split[0].Trim()] = split[1].Trim();
}

return settings;
}

private static string? FindLibPython(string home, Version? maybeVersion)
{
// TODO: Check whether there is a .dll/.so/.dylib next to the executable

if (maybeVersion is Version version)
{
return FindLibPythonInHome(home, version);
}

return null;
}

private static string? FindLibPythonInHome(string home, Version version)
{
var libPythonName = GetDefaultDllName(version);

List<string> pathsToCheck = new();
if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
{
var arch = RuntimeInformation.ProcessArchitecture;
if (arch == Architecture.X64 || arch == Architecture.Arm64)
{
// multilib systems
pathsToCheck.Add("../lib64");
}
pathsToCheck.Add("../lib");
}
else if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
{
pathsToCheck.Add(".");
}
else
{
pathsToCheck.Add("../lib");
}

return pathsToCheck
.Select(path => Path.Combine(home, path, libPythonName))
.FirstOrDefault(File.Exists);
}

private static string ProgramNameFromPath(string path)
{
if (Runtime.IsWindows)
{
return Path.Combine(path, "Scripts", "python.exe");
}
else
{
return Path.Combine(path, "bin", "python");
}
}

internal static string GetDefaultDllName(Version version)
{
string prefix = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "" : "lib";

string suffix = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
? Invariant($"{version.Major}{version.Minor}")
: Invariant($"{version.Major}.{version.Minor}");

string ext = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? ".dll"
: RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ? ".dylib"
: ".so";

return prefix + "python" + suffix + ext;
}
}
7 changes: 4 additions & 3 deletions tools/geninterop/geninterop.py
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