Add shell command (#201)

* Add shell command

* Make shell command Python2-compatible

* Add provisional Windows support; handle unset SHELL variable

* Reformatted with black

* Handle already activated virtualenvs

* Add comments to shell command code

* Remove splat operator to support Python 2

* Use "1" for POETRY_ACTIVE instead of virtualenv path

* Handle non-existing virtualenv when virtualenvs.create is false

* Handle unexisting virtualenvs in a broader way

* Check if POETRY_ACTIVE is specifically set to a true value

* Use utils.shell to get path to running shell

poetry/console/application.py

@@ -28,6 +28,7 @@ from .commands import RemoveCommand
 from .commands import RunCommand
 from .commands import ScriptCommand
 from .commands import SearchCommand
+from .commands import ShellCommand
 from .commands import ShowCommand
 from .commands import UpdateCommand
 from .commands import VersionCommand
@@ -119,6 +120,7 @@ class Application(BaseApplication):
             RunCommand(),
             ScriptCommand(),
             SearchCommand(),
+            ShellCommand(),
             ShowCommand(),
             UpdateCommand(),
             VersionCommand(),

poetry/console/commands/__init__.py

@@ -13,6 +13,7 @@ from .remove import RemoveCommand
 from .run import RunCommand
 from .script import ScriptCommand
 from .search import SearchCommand
+from .shell import ShellCommand
 from .show import ShowCommand
 from .update import UpdateCommand
 from .version import VersionCommand

poetry/console/commands/shell.py

+from os import environ
+from distutils.util import strtobool
+
+from .venv_command import VenvCommand
+
+
+class ShellCommand(VenvCommand):
+    """
+    Spawns a shell within the virtual environment.
+
+    shell [options]
+    """
+
+    help = """The <info>shell</> command spawns a shell, according to the
+<comment>$SHELL</> environment variable, within the virtual environment.
+If one doesn't exist yet, it will be created.
+"""
+
+    def handle(self):
+        from poetry.utils.shell import Shell
+
+        # Check if it's already activated or doesn't exist and won't be created
+        if strtobool(environ.get("POETRY_ACTIVE", "0")) or not self.venv.is_venv():
+            current_venv = environ.get("VIRTUAL_ENV")
+
+            if current_venv:
+                self.line(
+                    "Virtual environment already activated: "
+                    "<info>{}</>".format(current_venv)
+                )
+
+            else:
+                self.error("Virtual environment wasn't found")
+
+            return
+
+        self.line("Spawning shell within <info>{}</>".format(self.venv.venv))
+
+        # Setting this to avoid spawning unnecessary nested shells
+        environ["POETRY_ACTIVE"] = "1"
+        shell = Shell.get()
+        self.venv.execute(shell.path)
+        environ.pop("POETRY_ACTIVE")