On windows, the venv module does not copy the correct python exe if the current running exe (eg sys.executable) has been renamed (eg, named python3.exe)

venv will only make copies of python.exe, pythonw.exe, python_d.exe or pythonw_d.exe.

If for example the python executable has been renamed from python.exe to python3.exe (eg, to co-exist in a system where multiple pythons are on PATH) then this can fail with errors like:

Error: [WinError 2] The system cannot find the file specified

When venv tries to run pip in the new environment.

If the running python executable is a differently named copy then errors like the one described in https://bugs.python.org/issue40588 are seen.

This may also cause https://bugs.python.org/issue35644

I just encountered the same behavior. Steps to reproduce:

* Install Python 3 (I used 3.9.5) on Windows
* Use the Admin console to create a python3.exe link, e.g.

    cd "c:/Users/niklas/AppData/Local/Programs/Python/Python39"
    mklink python3.exe python.exe

* Use python3.exe to create a venv, e.g.

    python3 -m venv

The environment is created up until the point _setup_pip() is called in venv, which causes the following error to be printed:

    Error: [WinError 2] The system cannot find the file specified

Running venv from the interpreter gives the full stack trace.

    $ python3 -c 'import venv; venv.main([".venv"])'
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\venv\__init__.py", line 491, in main
        builder.create(d)
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\venv\__init__.py", line 75, in create
        self._setup_pip(context)
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\venv\__init__.py", line 299, in _setup_pip
        subprocess.check_output(cmd, stderr=subprocess.STDOUT)
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\subprocess.py", line 424, in check_output
        return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\subprocess.py", line 505, in run
        with Popen(*popenargs, **kwargs) as process:
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\subprocess.py", line 951, in __init__
        self._execute_child(args, executable, preexec_fn, close_fds,
      File "C:\Users\niklas\AppData\Local\Programs\Python\Python39\lib\subprocess.py", line 1420, in _execute_child
        hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
    FileNotFoundError: [WinError 2] The system cannot find the file specified

To complete my previous comment, patching the function to see the command that is invoked, you can see it tries to invoke 'python3.exe' (seemingly derived from sys.executable) in the venv but the venv only contains 'python.exe'.

['C:\\Users\\niklas\\dotfiles\\.venv\\Scripts\\python3.exe', '-Im', 'ensurepip', '--upgrade', '--default-pip']

Hey, can I request a backport of this change? For my use case, 3.9+ would be great, but going back to 3.7 should be viable? I trust your judgement :)

I'll happily create the PRs for the backport, but it looks like the bug has to be indicated as "needs backport to X.Y" by Python maintainers first (https://devguide.python.org/gitbootcamp/?highlight=backport#backporting-merged-changes)

3.10 and 3.9 - OK, but 3. is security fixes only, I'm afraid.

*3.8, I meant.

That's great, thanks!

New changeset bb8d645f3a09645686cf8f66bd46dcfa4efac713 by Miss Islington (bot) in branch '3.10':
[3.10] bpo-43749: Ensure current exe is copied when using venv on windows (GH-25216) (GH-30034)
https://github.com/python/cpython/commit/bb8d645f3a09645686cf8f66bd46dcfa4efac713

New changeset bad16f0cf71a6b11ef62f86be6b3d3567cd70a16 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-43749: Ensure current exe is copied when using venv on windows (GH-25216) (GH-30033)
https://github.com/python/cpython/commit/bad16f0cf71a6b11ef62f86be6b3d3567cd70a16

The Windows implementation of symlink_or_copy() actually copies "python.exe" and "pythonw.exe" launchers from "Lib/venv/scripts/nt". One cannot simply copy the "python3.exe" executable because the required DLLs aren't copied. If this seemed to work when testing, it was only because the installation directory was in PATH. The solution that actually works is to copy the launcher as "python3.exe".

We'd also need to update the launcher to launch the executable with its name, which it currently doesn't do. I was looking at this recently for some other reason.

The code to copy a file could be rewritten to use a regex match. For example:

            # Copy src to dst. If src is a base executable, copy a launcher.
            dirname, filename = os.path.split(src)
            m = re.match(r'(pythonw?)[0-9._]*((?:_d)?(?:\.exe|\.pdb))$',
                    filename.lower())
            if m is not None:
                src = os.path.join(os.path.dirname(__file__),
                        'scripts', 'nt', m.group(1) + m.group(2))
                # If the base environment is a Python source build, use
                # the launcher in the build directory instead of
                # "Lib/venv/scripts/nt".
                if sysconfig.is_python_build(True) or not os.path.isfile(src):
                    basename = ('venvlauncher' if m.group(1) == 'python' else
                                'venvwlauncher')
                    src = os.path.join(dirname, basename + m.group(2))