Virtual environments and pip

import sys
from pathlib import Path


def in_venv() -> bool:
    """True when this interpreter runs from a virtual environment."""
    # Compare the two prefixes the venv docs name.
    return False


def env_python(env: Path, platform: str = sys.platform) -> Path:
    """The interpreter inside the virtual environment env, for this platform."""
    # Windows ("win32") keeps it somewhere else.
    return env / "bin" / "python"


if __name__ == "__main__":
    print("in a venv:", in_venv())
    print("interpreter:", env_python(Path(".venv")))

import sys
from pathlib import Path
from unittest.mock import patch

import main


def test_in_venv_true():
    """in_venv() is True when sys.prefix differs from sys.base_prefix"""
    with patch.object(sys, "prefix", "/project/.venv"), patch.object(sys, "base_prefix", "/usr/local"):
        assert main.in_venv() is True, "the prefixes differ, so this is a virtual environment"


def test_in_venv_false():
    """in_venv() is False when both prefixes are the same"""
    with patch.object(sys, "prefix", "/usr/local"), patch.object(sys, "base_prefix", "/usr/local"):
        assert main.in_venv() is False, "the prefixes are equal, so this is not a virtual environment"


def test_posix_path():
    """On Linux and macOS the interpreter is bin/python"""
    for platform in ("linux", "darwin"):
        got = main.env_python(Path(".venv"), platform)
        assert got == Path(".venv", "bin", "python"), f"{platform}: got {got}"


def test_windows_path():
    """On Windows the interpreter is Scripts/python.exe"""
    got = main.env_python(Path(".venv"), "win32")
    assert got == Path(".venv", "Scripts", "python.exe"), f"win32: got {got}"

import sys
import venv
from pathlib import Path


def make_env(path: Path) -> Path:
    """Create a virtual environment at path and return its interpreter."""
    # Create the environment first, without pip, then return its interpreter.
    if sys.platform == "win32":
        return path / "Scripts" / "python.exe"
    return path / "bin" / "python"


if __name__ == "__main__":
    python = make_env(Path(".venv"))
    print("created:", python.exists())
    print("run it with:", python)

import subprocess
import tempfile
from pathlib import Path

import main


def test_creates_environment():
    """make_env writes pyvenv.cfg into the new folder"""
    with tempfile.TemporaryDirectory() as tmp:
        env = Path(tmp) / ".venv"
        main.make_env(env)
        assert (env / "pyvenv.cfg").exists(), "no pyvenv.cfg: call venv.create(path, with_pip=False)"


def test_returns_interpreter():
    """make_env returns the path of the new interpreter, and it exists"""
    with tempfile.TemporaryDirectory() as tmp:
        python = main.make_env(Path(tmp) / ".venv")
        assert python.exists(), f"{python} does not exist"


def test_interpreter_is_in_the_venv():
    """The returned interpreter reports that it runs in a virtual environment"""
    with tempfile.TemporaryDirectory() as tmp:
        python = main.make_env(Path(tmp) / ".venv")
        check = subprocess.run(
            [str(python), "-c", "import sys; print(sys.prefix != sys.base_prefix)"],
            capture_output=True,
            text=True,
        )
        assert check.stdout.strip() == "True", f"{python} printed {check.stdout.strip()!r}{check.stderr}"