First stab at reducing startup time

src/pip/_internal/__init__.py

@@ -37,14 +37,13 @@
         else:
             securetransport.inject_into_urllib3()
 
-from pip._internal.cli.autocompletion import autocomplete
 from pip._internal.cli.main_parser import parse_command
 from pip._internal.commands import commands_dict
 from pip._internal.exceptions import PipError
 from pip._internal.utils import deprecation
+
 from pip._internal.vcs import git, mercurial, subversion, bazaar  # noqa
 from pip._vendor.urllib3.exceptions import InsecureRequestWarning
-
 logger = logging.getLogger(__name__)
 
 # Hide the InsecureRequestWarning from urllib3
@@ -58,7 +57,10 @@ def main(args=None):
     # Configure our deprecation warnings to be sent through loggers
     deprecation.install_warning_logger()
 
-    autocomplete()
+    if 'PIP_AUTO_COMPLETE' in os.environ:
+        from pip._internal.cli.autocompletion import autocomplete
+        autocomplete()
+        return 1
 
     try:
         cmd_name, cmd_args = parse_command(args)

src/pip/_internal/cli/autocompletion.py

@@ -98,7 +98,6 @@ def autocomplete():
                 subcommands = auto_complete_paths(current, completion_type)
 
         print(' '.join([x for x in subcommands if x.startswith(current)]))
-    sys.exit(1)
 
 
 def get_path_completion_type(cwords, cword, opts):

src/pip/_internal/cli/base_command.py

@@ -2,38 +2,7 @@
 from __future__ import absolute_import, print_function
 
 import logging
-import logging.config
-import optparse
-import os
-import platform
-import sys
-import traceback
-
-from pip._internal.cli import cmdoptions
-from pip._internal.cli.parser import (
-    ConfigOptionParser, UpdatingDefaultsHelpFormatter,
-)
-from pip._internal.cli.status_codes import (
-    ERROR, PREVIOUS_BUILD_DIR_ERROR, SUCCESS, UNKNOWN_ERROR,
-    VIRTUALENV_NOT_FOUND,
-)
-from pip._internal.download import PipSession
-from pip._internal.exceptions import (
-    BadCommand, CommandError, InstallationError, PreviousBuildDirError,
-    UninstallationError,
-)
-from pip._internal.index import PackageFinder
-from pip._internal.locations import running_under_virtualenv
-from pip._internal.req.constructors import (
-    install_req_from_editable, install_req_from_line,
-)
-from pip._internal.req.req_file import parse_requirements
-from pip._internal.utils.deprecation import deprecated
-from pip._internal.utils.logging import BrokenStdoutLoggingError, setup_logging
-from pip._internal.utils.misc import (
-    get_prog, normalize_path, redact_password_from_url,
-)
-from pip._internal.utils.outdated import pip_version_check
+
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 if MYPY_CHECK_RUNNING:
@@ -54,6 +23,15 @@ class Command(object):
 
     def __init__(self, isolated=False):
         # type: (bool) -> None
+
+        import optparse
+
+        from pip._internal.cli import cmdoptions
+        from pip._internal.cli.parser import (
+            ConfigOptionParser, UpdatingDefaultsHelpFormatter,
+        )
+        from pip._internal.utils.misc_fast_import import get_prog
+
         parser_kw = {
             'usage': self.usage,
             'prog': '%s %s' % (get_prog(), self.name),
@@ -97,6 +75,12 @@ def _get_index_urls(cls, options):
 
     def _build_session(self, options, retries=None, timeout=None):
         # type: (Values, Optional[int], Optional[int]) -> PipSession
+        import os
+
+        from pip._internal.download import PipSession
+        from pip._internal.utils.misc import (
+            normalize_path, )
+
         session = PipSession(
             cache=(
                 normalize_path(os.path.join(options.cache_dir, "http"))
@@ -140,6 +124,25 @@ def parse_args(self, args):
 
     def main(self, args):
         # type: (List[str]) -> int
+        import logging.config
+        import os
+        import platform
+        import sys
+        import traceback
+
+        from pip._internal.cli.status_codes import (
+            ERROR, PREVIOUS_BUILD_DIR_ERROR, SUCCESS, UNKNOWN_ERROR,
+            VIRTUALENV_NOT_FOUND,
+        )
+        from pip._internal.exceptions import (
+            BadCommand, CommandError, InstallationError, PreviousBuildDirError,
+            UninstallationError,
+        )
+        from pip._internal.locations import running_under_virtualenv
+        from pip._internal.utils.deprecation import deprecated
+        from pip._internal.utils.logging import BrokenStdoutLoggingError, setup_logging
+        from pip._internal.utils.outdated import pip_version_check
+
         options, args = self.parse_args(args)
 
         # Set verbosity so that it can be used elsewhere.
@@ -268,6 +271,15 @@ def populate_requirement_set(requirement_set,  # type: RequirementSet
         # NOTE: As a side-effect, options.require_hashes and
         #       requirement_set.require_hashes may be updated
 
+        from pip._internal.download import PipSession
+        from pip._internal.exceptions import (
+            CommandError, )
+        from pip._internal.index import PackageFinder
+        from pip._internal.req.constructors import (
+            install_req_from_editable, install_req_from_line,
+        )
+        from pip._internal.req.req_file import parse_requirements
+
         for filename in options.constraints:
             for req_to_add in parse_requirements(
                     filename,
@@ -329,6 +341,13 @@ def _build_package_finder(
         implementation=None    # type: Optional[str]
     ):
         # type: (...) -> PackageFinder
+
+        from pip._internal.download import PipSession
+        from pip._internal.index import PackageFinder
+        from pip._internal.utils.misc import (
+            redact_password_from_url,
+        )
+
         """
         Create a package finder appropriate to this requirement command.
         """

src/pip/_internal/cli/main_parser.py

@@ -4,18 +4,7 @@
 import os
 import sys
 
-from pip import __version__
-from pip._internal.cli import cmdoptions
-from pip._internal.cli.parser import (
-    ConfigOptionParser, UpdatingDefaultsHelpFormatter,
-)
-from pip._internal.commands import (
-    commands_dict, get_similar_commands, get_summaries,
-)
-from pip._internal.exceptions import CommandError
-from pip._internal.utils.misc import get_prog
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
-
 if MYPY_CHECK_RUNNING:
     from typing import Tuple, List
 
@@ -28,6 +17,16 @@ def create_main_parser():
     """Creates and returns the main parser for pip's CLI
     """
 
+    from pip import __version__
+    from pip._internal.cli import cmdoptions
+    from pip._internal.cli.parser import (
+        ConfigOptionParser, UpdatingDefaultsHelpFormatter,
+    )
+    from pip._internal.commands import (
+        get_summaries,
+    )
+    from pip._internal.utils.misc_fast_import import get_prog
+
     parser_kw = {
         'usage': '\n%prog <command> [options]',
         'add_help_option': False,
@@ -63,6 +62,11 @@ def create_main_parser():
 
 def parse_command(args):
     # type: (List[str]) -> Tuple[str, List[str]]
+    from pip._internal.commands import (
+        commands_dict, get_similar_commands,
+    )
+    from pip._internal.exceptions import CommandError
+
     parser = create_main_parser()
 
     # Note: parser calls disable_interspersed_args(), so the result of this

src/pip/_internal/commands/check.py

@@ -1,9 +1,6 @@
 import logging
 
 from pip._internal.cli.base_command import Command
-from pip._internal.operations.check import (
-    check_package_set, create_package_set_from_installed,
-)
 
 logger = logging.getLogger(__name__)
 
@@ -16,6 +13,9 @@ class CheckCommand(Command):
     summary = 'Verify installed packages have compatible dependencies.'
 
     def run(self, options, args):
+        from pip._internal.operations.check import (
+            check_package_set, create_package_set_from_installed,
+        )
         package_set, parsing_probs = create_package_set_from_installed()
         missing, conflicting = check_package_set(package_set)
 

src/pip/_internal/commands/completion.py

@@ -4,7 +4,8 @@
 import textwrap
 
 from pip._internal.cli.base_command import Command
-from pip._internal.utils.misc import get_prog
+from pip._internal.utils.misc_fast_import import get_prog
+
 
 BASE_COMPLETION = """
 # pip %(shell)s completion start%(script)s# pip %(shell)s completion end

src/pip/_internal/commands/configuration.py

@@ -3,12 +3,7 @@
 import subprocess
 
 from pip._internal.cli.base_command import Command
-from pip._internal.cli.status_codes import ERROR, SUCCESS
-from pip._internal.configuration import Configuration, kinds
-from pip._internal.exceptions import PipError
-from pip._internal.locations import running_under_virtualenv, site_config_file
-from pip._internal.utils.deprecation import deprecated
-from pip._internal.utils.misc import get_prog
+from pip._internal.utils.misc_fast_import import get_prog
 
 logger = logging.getLogger(__name__)
 
@@ -96,6 +91,10 @@ def __init__(self, *args, **kwargs):
         self.parser.insert_option_group(0, self.cmd_opts)
 
     def run(self, options, args):
+        from pip._internal.cli.status_codes import ERROR, SUCCESS
+        from pip._internal.configuration import Configuration
+        from pip._internal.exceptions import PipError
+
         handlers = {
             "list": self.list_values,
             "edit": self.open_in_editor,
@@ -139,6 +138,11 @@ def run(self, options, args):
         return SUCCESS
 
     def _determine_file(self, options, need_value):
+        from pip._internal.configuration import kinds
+        from pip._internal.exceptions import PipError
+        from pip._internal.locations import running_under_virtualenv, site_config_file
+        from pip._internal.utils.deprecation import deprecated
+
         # Convert legacy venv_file option to site_file or error
         if options.venv_file and not options.site_file:
             if running_under_virtualenv():
@@ -201,6 +205,8 @@ def unset_name(self, options, args):
         self._save_configuration()
 
     def open_in_editor(self, options, args):
+        from pip._internal.exceptions import PipError
+
         editor = self._determine_editor(options)
 
         fname = self.configuration.get_file_to_edit()
@@ -218,6 +224,7 @@ def open_in_editor(self, options, args):
     def _get_n_args(self, args, example, n):
         """Helper to make sure the command got the right number of arguments
         """
+        from pip._internal.exceptions import PipError
         if len(args) != n:
             msg = (
                 'Got unexpected number of arguments, expected {}. '
@@ -231,6 +238,7 @@ def _get_n_args(self, args, example, n):
             return args
 
     def _save_configuration(self):
+        from pip._internal.exceptions import PipError
         # We successfully ran a modifying command. Need to save the
         # configuration.
         try:
@@ -243,6 +251,7 @@ def _save_configuration(self):
             raise PipError("Internal Error.")
 
     def _determine_editor(self, options):
+        from pip._internal.exceptions import PipError
         if options.editor is not None:
             return options.editor
         elif "VISUAL" in os.environ:

src/pip/_internal/commands/download.py

@@ -3,15 +3,7 @@
 import logging
 import os
 
-from pip._internal.cli import cmdoptions
 from pip._internal.cli.base_command import RequirementCommand
-from pip._internal.operations.prepare import RequirementPreparer
-from pip._internal.req import RequirementSet
-from pip._internal.req.req_tracker import RequirementTracker
-from pip._internal.resolve import Resolver
-from pip._internal.utils.filesystem import check_path_owner
-from pip._internal.utils.misc import ensure_dir, normalize_path
-from pip._internal.utils.temp_dir import TempDirectory
 
 logger = logging.getLogger(__name__)
 
@@ -42,6 +34,8 @@ class DownloadCommand(RequirementCommand):
     def __init__(self, *args, **kw):
         super(DownloadCommand, self).__init__(*args, **kw)
 
+        from pip._internal.cli import cmdoptions
+
         cmd_opts = self.cmd_opts
 
         cmd_opts.add_option(cmdoptions.constraints())
@@ -83,6 +77,15 @@ def __init__(self, *args, **kw):
         self.parser.insert_option_group(0, cmd_opts)
 
     def run(self, options, args):
+        from pip._internal.cli import cmdoptions
+        from pip._internal.operations.prepare import RequirementPreparer
+        from pip._internal.req import RequirementSet
+        from pip._internal.req.req_tracker import RequirementTracker
+        from pip._internal.resolve import Resolver
+        from pip._internal.utils.filesystem import check_path_owner
+        from pip._internal.utils.misc import ensure_dir, normalize_path
+        from pip._internal.utils.temp_dir import TempDirectory
+
         options.ignore_installed = True
         # editable doesn't really make sense for `pip download`, but the bowels
         # of the RequirementSet code require that property.

src/pip/_internal/commands/freeze.py

@@ -2,11 +2,7 @@
 
 import sys
 
-from pip._internal.cache import WheelCache
 from pip._internal.cli.base_command import Command
-from pip._internal.models.format_control import FormatControl
-from pip._internal.operations.freeze import freeze
-from pip._internal.utils.compat import stdlib_pkgs
 
 DEV_PKGS = {'pip', 'setuptools', 'distribute', 'wheel'}
 
@@ -71,6 +67,11 @@ def __init__(self, *args, **kw):
         self.parser.insert_option_group(0, self.cmd_opts)
 
     def run(self, options, args):
+        from pip._internal.cache import WheelCache
+        from pip._internal.models.format_control import FormatControl
+        from pip._internal.operations.freeze import freeze
+        from pip._internal.utils.compat import stdlib_pkgs
+
         format_control = FormatControl(set(), set())
         wheel_cache = WheelCache(options.cache_dir, format_control)
         skip = set(stdlib_pkgs)