Fix handling of Python versions compatibility

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Fixed installation of Poetry git dependencies with a build system.
 - Fixed possible errors when resolving dependencies for specific packages.
+- Fixed handling of Python versions compatibility.
 
 
 ## [0.12.4] - 2018-10-21

poetry/console/commands/env_command.py

@@ -8,10 +8,27 @@ class EnvCommand(Command):
         super(EnvCommand, self).__init__()
 
     def initialize(self, i, o):
+        from poetry.semver import parse_constraint
         from poetry.utils.env import Env
 
         super(EnvCommand, self).initialize(i, o)
 
+        # Checking compatibility of the current environment with
+        # the python dependency specified in pyproject.toml
+        current_env = Env.get()
+        supported_python = self.poetry.package.python_constraint
+        current_python = parse_constraint(
+            ".".join(str(v) for v in current_env.version_info[:3])
+        )
+
+        if not supported_python.allows(current_python):
+            raise RuntimeError(
+                "The current Python version ({}) is not supported by the project ({})\n"
+                "Please activate a compatible Python version.".format(
+                    current_python, self.poetry.package.python_versions
+                )
+            )
+
         self._env = Env.create_venv(
             o, self.poetry.package.name, cwd=self.poetry.file.parent
         )

poetry/console/commands/init.py

@@ -37,6 +37,7 @@ The <info>init</info> command creates a basic <comment>pyproject.toml</> file in
     def handle(self):
         from poetry.layouts import layout
         from poetry.utils._compat import Path
+        from poetry.utils.env import Env
         from poetry.vcs.git import GitConfig
 
         if (Path.cwd() / "pyproject.toml").exists():
@@ -101,7 +102,16 @@ The <info>init</info> command creates a basic <comment>pyproject.toml</> file in
         question.validator = self._validate_license
         license = self.ask(question)
 
-        question = self.create_question("Compatible Python versions [*]: ", default="*")
+        current_env = Env.get()
+        default_python = "^{}".format(
+            ".".join(str(v) for v in current_env.version_info[:2])
+        )
+        question = self.create_question(
+            "Compatible Python versions [<comment>{}</comment>]: ".format(
+                default_python
+            ),
+            default=default_python,
+        )
         python = self.ask(question)
 
         self.line("")

poetry/console/commands/new.py

@@ -14,6 +14,7 @@ class NewCommand(Command):
     def handle(self):
         from poetry.layouts import layout
         from poetry.utils._compat import Path
+        from poetry.utils.env import Env
         from poetry.vcs.git import GitConfig
 
         if self.option("src"):
@@ -44,7 +45,17 @@ class NewCommand(Command):
             if author_email:
                 author += " <{}>".format(author_email)
 
-        layout_ = layout_(name, "0.1.0", author=author, readme_format=readme_format)
+        current_env = Env.get()
+        default_python = "^{}".format(
+            ".".join(str(v) for v in current_env.version_info[:2])
+        )
+        layout_ = layout_(
+            name,
+            "0.1.0",
+            author=author,
+            readme_format=readme_format,
+            python=default_python,
+        )
         layout_.create(path)
 
         self.line(

poetry/utils/env.py

@@ -516,3 +516,19 @@ class NullEnv(SystemEnv):
 
     def _bin(self, bin):
         return bin
+
+
+class MockEnv(NullEnv):
+    def __init__(self, version_info=(3, 7, 0), python_implementation="cpython"):
+        super(MockEnv, self).__init__()
+
+        self._version_info = version_info
+        self._python_implementation = python_implementation
+
+    @property
+    def version_info(self):  # type: () -> Tuple[int]
+        return self._version_info
+
+    @property
+    def python_implementation(self):  # type: () -> str
+        return self._python_implementation

tests/console/commands/test_init.py

@@ -148,7 +148,7 @@ description = ""
 authors = ["Your Name <you@example.com>"]
 
 [tool.poetry.dependencies]
-python = "*"
+python = "^3.7"
 
 [tool.poetry.dev-dependencies]
 """

tests/console/conftest.py

@@ -17,6 +17,8 @@ from poetry.packages import Locker as BaseLocker
 from poetry.repositories import Pool
 from poetry.repositories import Repository
 from poetry.utils._compat import Path
+from poetry.utils.env import Env
+from poetry.utils.env import MockEnv
 from poetry.utils.toml_file import TomlFile
 
 
@@ -48,6 +50,8 @@ def installed():
 
 @pytest.fixture(autouse=True)
 def setup(mocker, installer, installed):
+    Env._env = MockEnv()
+
     # Set Installer's installer
     p = mocker.patch("poetry.installation.installer.Installer._get_installer")
     p.return_value = installer
@@ -74,6 +78,7 @@ def setup(mocker, installer, installed):
 
     os.environ.clear()
     os.environ.update(environ)
+    Env._env = None
 
 
 class Application(BaseApplication):