Make imports lazier (#3938)

This change speeds up poetry command start time by 50ms compared to
current master and around 250ms compared to 1.1.5.

Relates-to: #3502

poetry/console/commands/check.py

 from pathlib import Path
 
-from poetry.core.pyproject.toml import PyProjectTOML
-from poetry.factory import Factory
-
 from .command import Command
 
 
@@ -12,6 +9,9 @@ class CheckCommand(Command):
     description = "Checks the validity of the <comment>pyproject.toml</comment> file."
 
     def handle(self) -> int:
+        from poetry.core.pyproject.toml import PyProjectTOML
+        from poetry.factory import Factory
+
         # Load poetry config and display errors, if any
         poetry_file = Factory.locate(Path.cwd())
         config = PyProjectTOML(poetry_file).poetry_config

poetry/console/commands/remove.py

@@ -5,7 +5,7 @@ from typing import List
 from cleo.helpers import argument
 from cleo.helpers import option
 
-from .installer_command import InstallerCommand
+from poetry.console.commands.installer_command import InstallerCommand
 
 
 class RemoveCommand(InstallerCommand):

poetry/console/commands/source/add.py

@@ -10,8 +10,6 @@ from tomlkit.items import Table
 
 from poetry.config.source import Source
 from poetry.console.commands.command import Command
-from poetry.factory import Factory
-from poetry.repositories import Pool
 
 
 class SourceAddCommand(Command):
@@ -39,7 +37,7 @@ class SourceAddCommand(Command):
     ]
 
     @staticmethod
-    def source_to_table(source: Source) -> Table:
+    def source_to_table(source: "Source") -> Table:
         source_table: Table = table()
         for key, value in source.to_dict().items():
             source_table.add(key, value)
@@ -47,6 +45,9 @@ class SourceAddCommand(Command):
         return source_table
 
     def handle(self) -> Optional[int]:
+        from poetry.factory import Factory
+        from poetry.repositories import Pool
+
         name = self.argument("name")
         url = self.argument("url")
         is_default = self.option("default")

poetry/factory.py

@@ -16,7 +16,6 @@ from poetry.packages.locker import Locker
 from poetry.packages.project_package import ProjectPackage
 from poetry.plugins.plugin_manager import PluginManager
 from poetry.poetry import Poetry
-from poetry.repositories.pypi_repository import PyPiRepository
 
 
 if TYPE_CHECKING:
@@ -156,6 +155,8 @@ class Factory(BaseFactory):
             if io.is_debug():
                 io.write_line("Deactivating the PyPI repository")
         else:
+            from poetry.repositories.pypi_repository import PyPiRepository
+
             default = not poetry.pool.has_primary_repositories()
             poetry.pool.add_repository(PyPiRepository(), default, not default)
 

poetry/installation/chooser.py

 import re
 
+from typing import TYPE_CHECKING
 from typing import List
 from typing import Optional
 from typing import Tuple
@@ -8,11 +9,14 @@ from packaging.tags import Tag
 
 from poetry.core.packages.package import Package
 from poetry.core.packages.utils.link import Link
-from poetry.repositories.pool import Pool
 from poetry.utils.env import Env
 from poetry.utils.patterns import wheel_file_re
 
 
+if TYPE_CHECKING:
+    from poetry.repositories.pool import Pool
+
+
 class InvalidWheelName(Exception):
     pass
 
@@ -49,7 +53,7 @@ class Chooser:
     A Chooser chooses an appropriate release archive for packages.
     """
 
-    def __init__(self, pool: Pool, env: Env) -> None:
+    def __init__(self, pool: "Pool", env: Env) -> None:
         self._pool = pool
         self._env = env
 

poetry/installation/pip_installer.py

@@ -12,7 +12,6 @@ from cleo.io.io import IO
 
 from poetry.core.pyproject.toml import PyProjectTOML
 from poetry.installation.base_installer import BaseInstaller
-from poetry.repositories.pool import Pool
 from poetry.utils._compat import encode
 from poetry.utils.env import Env
 from poetry.utils.helpers import safe_rmtree
@@ -22,10 +21,11 @@ from poetry.utils.pip import pip_install
 
 if TYPE_CHECKING:
     from poetry.core.packages.package import Package
+    from poetry.repositories.pool import Pool
 
 
 class PipInstaller(BaseInstaller):
-    def __init__(self, env: Env, io: IO, pool: Pool) -> None:
+    def __init__(self, env: Env, io: IO, pool: "Pool") -> None:
         self._env = env
         self._io = io
         self._pool = pool

poetry/packages/locker.py

@@ -24,8 +24,6 @@ from tomlkit import item
 from tomlkit import table
 from tomlkit.exceptions import TOMLKitError
 
-import poetry.repositories
-
 from poetry.core.packages.dependency import Dependency
 from poetry.core.packages.package import Package
 from poetry.core.semver.helpers import parse_constraint
@@ -40,6 +38,8 @@ from poetry.utils.extras import get_extra_package_names
 if TYPE_CHECKING:
     from tomlkit.toml_document import TOMLDocument
 
+    from poetry.repositories import Repository
+
 logger = logging.getLogger(__name__)
 
 
@@ -87,19 +87,18 @@ class Locker:
 
         return False
 
-    def locked_repository(
-        self, with_dev_reqs: bool = False
-    ) -> poetry.repositories.Repository:
+    def locked_repository(self, with_dev_reqs: bool = False) -> "Repository":
         """
         Searches and returns a repository of locked packages.
         """
         from poetry.factory import Factory
+        from poetry.repositories import Repository
 
         if not self.is_locked():
-            return poetry.repositories.Repository()
+            return Repository()
 
         lock_data = self.lock_data
-        packages = poetry.repositories.Repository()
+        packages = Repository()
 
         if with_dev_reqs:
             locked_packages = lock_data["package"]

poetry/utils/helpers.py

@@ -6,6 +6,7 @@ import tempfile
 
 from contextlib import contextmanager
 from pathlib import Path
+from typing import TYPE_CHECKING
 from typing import Any
 from typing import Callable
 from typing import Dict
@@ -13,10 +14,7 @@ from typing import Iterator
 from typing import List
 from typing import Optional
 
-import requests
-
 from poetry.config.config import Config
-from poetry.core.packages.package import Package
 
 
 try:
@@ -25,6 +23,12 @@ except ImportError:
     from collections import Mapping
 
 
+if TYPE_CHECKING:
+    from requests import Session
+
+    from poetry.core.packages.package import Package
+
+
 _canonicalize_regex = re.compile("[-_]+")
 
 
@@ -92,9 +96,11 @@ def merge_dicts(d1: Dict, d2: Dict) -> None:
 def download_file(
     url: str,
     dest: str,
-    session: Optional[requests.Session] = None,
+    session: Optional["Session"] = None,
     chunk_size: int = 1024,
 ) -> None:
+    import requests
+
     get = requests.get if not session else session.get
 
     with get(url, stream=True) as response:
@@ -107,7 +113,7 @@ def download_file(
 
 
 def get_package_version_display_string(
-    package: Package, root: Optional[Path] = None
+    package: "Package", root: Optional[Path] = None
 ) -> str:
     if package.source_type in ["file", "directory"] and root:
         return "{} {}".format(