bpo-30152: Reduce the number of imports for argparse.

Lib/argparse.py

@@ -84,15 +84,12 @@
 
 
 import collections as _collections
-import copy as _copy
 import os as _os
 import re as _re
 import sys as _sys
-import textwrap as _textwrap
 
 from gettext import gettext as _, ngettext
 
-
 SUPPRESS = '==SUPPRESS=='
 
 OPTIONAL = '?'
@@ -137,10 +134,16 @@ def _get_args(self):
  return []
 
 
-def _ensure_value(namespace, name, value):
- if getattr(namespace, name, None) is None:
- setattr(namespace, name, value)
- return getattr(namespace, name)
+def _copy_items(items):
+ if items is None:
+ return []
+ # The copy module is used only in the 'append' and 'append_const'
+ # actions, and it is needed only when the default value isn't a list.
+ # Delay its import for speeding up the common case.
+ if type(items) is list:
+ return items[:]
+ import copy
+ return copy.copy(items)
 
 
 # ===============
@@ -619,12 +622,17 @@ def _iter_indented_subactions(self, action):
 
  def _split_lines(self, text, width):
  text = self._whitespace_matcher.sub(' ', text).strip()
- return _textwrap.wrap(text, width)
+ # The textwrap module is used only for formatting help.
+ # Delay its import for speeding up the common usage of argparse.
+ import textwrap
+ return textwrap.wrap(text, width)
 
  def _fill_text(self, text, width, indent):
  text = self._whitespace_matcher.sub(' ', text).strip()
- return _textwrap.fill(text, width, initial_indent=indent,
- subsequent_indent=indent)
+ import textwrap
+ return textwrap.fill(text, width,
+ initial_indent=indent,
+ subsequent_indent=indent)
 
  def _get_help_string(self, action):
  return action.help
@@ -952,7 +960,8 @@ def __init__(self,
  metavar=metavar)
 
  def __call__(self, parser, namespace, values, option_string=None):
- items = _copy.copy(_ensure_value(namespace, self.dest, []))
+ items = getattr(namespace, self.dest, None)
+ items = _copy_items(items)
  items.append(values)
  setattr(namespace, self.dest, items)
 
@@ -978,7 +987,8 @@ def __init__(self,
  metavar=metavar)
 
  def __call__(self, parser, namespace, values, option_string=None):
- items = _copy.copy(_ensure_value(namespace, self.dest, []))
+ items = getattr(namespace, self.dest, None)
+ items = _copy_items(items)
  items.append(self.const)
  setattr(namespace, self.dest, items)
 
@@ -1000,8 +1010,10 @@ def __init__(self,
  help=help)
 
  def __call__(self, parser, namespace, values, option_string=None):
- new_count = _ensure_value(namespace, self.dest, 0) + 1
- setattr(namespace, self.dest, new_count)
+ count = getattr(namespace, self.dest, None)
+ if count is None:
+ count = 0
+ setattr(namespace, self.dest, count + 1)
 
 
 class _HelpAction(Action):

Lib/enum.py

@@ -1,7 +1,5 @@
 import sys
 from types import MappingProxyType, DynamicClassAttribute
-from functools import reduce
-from operator import or_ as _or_
 
 # try _collections first to reduce startup cost
 try:
@@ -744,11 +742,10 @@ def __xor__(self, other):
 
  def __invert__(self):
  members, uncovered = _decompose(self.__class__, self._value_)
- inverted_members = [
- m for m in self.__class__
- if m not in members and not m._value_ & self._value_
- ]
- inverted = reduce(_or_, inverted_members, self.__class__(0))
+ inverted = self.__class__(0)
+ for m in self.__class__:
+ if m not in members and not (m._value_ & self._value_):
+ inverted = inverted | m
  return self.__class__(inverted)
 
 

Lib/gettext.py

@@ -46,13 +46,10 @@
 # find this format documented anywhere.
 
 
-import copy
 import locale
 import os
 import re
-import struct
 import sys
-from errno import ENOENT
 
 
 __all__ = ['NullTranslations', 'GNUTranslations', 'Catalog',
@@ -342,7 +339,9 @@ def _get_versions(self, version):
 
  def _parse(self, fp):
  """Override this method to support alternative .mo formats."""
- unpack = struct.unpack
+ # Delay struct import for speeding up gettext import when .mo files
+ # are not used.
+ from struct import unpack
  filename = getattr(fp, 'name', '')
  # Parse the .mo file header, which consists of 5 little endian 32
  # bit words.
@@ -520,7 +519,9 @@ def translation(domain, localedir=None, languages=None,
  if not mofiles:
  if fallback:
  return NullTranslations()
- raise OSError(ENOENT, 'No translation file found for domain', domain)
+ from errno import ENOENT
+ raise FileNotFoundError(ENOENT,
+ 'No translation file found for domain', domain)
  # Avoid opening, reading, and parsing the .mo file after it's been done
  # once.
  result = None
@@ -533,6 +534,9 @@ def translation(domain, localedir=None, languages=None,
  # Copy the translation object to allow setting fallbacks and
  # output charset. All other instance data is shared with the
  # cached object.
+ # Delay copy import for speeding up gettext import when .mo files
+ # are not used.
+ import copy
  t = copy.copy(t)
  if codeset:
  t.set_output_charset(codeset)

Lib/locale.py

@@ -14,10 +14,9 @@
 import encodings
 import encodings.aliases
 import re
-import collections.abc
+import _collections_abc
 from builtins import str as _builtin_str
 import functools
-import warnings
 
 # Try importing the _locale module.
 #
@@ -215,7 +214,7 @@ def format_string(f, val, grouping=False, monetary=False):
  percents = list(_percent_re.finditer(f))
  new_f = _percent_re.sub('%s', f)
 
- if isinstance(val, collections.abc.Mapping):
+ if isinstance(val, _collections_abc.Mapping):
  new_val = []
  for perc in percents:
  if perc.group()[-1]=='%':
@@ -244,6 +243,7 @@ def format_string(f, val, grouping=False, monetary=False):
 
 def format(percent, value, grouping=False, monetary=False, *additional):
  """Deprecated, use format_string instead."""
+ import warnings
  warnings.warn(
  "This method will be removed in a future version of Python. "
  "Use 'locale.format_string()' instead.",

Lib/os.py

@@ -23,7 +23,7 @@
 
 #'
 import abc
-import sys, errno
+import sys
 import stat as st
 
 _names = sys.builtin_module_names
@@ -590,12 +590,10 @@ def _execvpe(file, args, env=None):
  argrest = (args,)
  env = environ
 
- head, tail = path.split(file)
- if head:
+ if path.dirname(file):
  exec_func(file, *argrest)
  return
- last_exc = saved_exc = None
- saved_tb = None
+ saved_exc = None
  path_list = get_exec_path(env)
  if name != 'nt':
  file = fsencode(file)
@@ -604,16 +602,15 @@ def _execvpe(file, args, env=None):
  fullname = path.join(dir, file)
  try:
  exec_func(fullname, *argrest)
+ except (FileNotFoundError, NotADirectoryError) as e:
+ last_exc = e
  except OSError as e:
  last_exc = e
- tb = sys.exc_info()[2]
- if (e.errno != errno.ENOENT and e.errno != errno.ENOTDIR
- and saved_exc is None):
+ if saved_exc is None:
  saved_exc = e
- saved_tb = tb
- if saved_exc:
- raise saved_exc.with_traceback(saved_tb)
- raise last_exc.with_traceback(tb)
+ if saved_exc is not None:
+ raise saved_exc
+ raise last_exc
 
 
 def get_exec_path(env=None):

Lib/pathlib.py

@@ -6,7 +6,7 @@
 import posixpath
 import re
 import sys
-from collections.abc import Sequence
+from _collections_abc import Sequence
 from errno import EINVAL, ENOENT, ENOTDIR
 from operator import attrgetter
 from stat import S_ISDIR, S_ISLNK, S_ISREG, S_ISSOCK, S_ISBLK, S_ISCHR, S_ISFIFO

Lib/types.py

@@ -172,9 +172,6 @@ def deleter(self, fdel):
  return result
 
 
-import functools as _functools
-import collections.abc as _collections_abc
-
 class _GeneratorWrapper:
  # TODO: Implement this in C.
  def __init__(self, gen):
@@ -247,7 +244,10 @@ def coroutine(func):
  # return generator-like objects (for instance generators
  # compiled with Cython).
 
- @_functools.wraps(func)
+ # Delay functools and _collections_abc import for speeding up types import.
+ import functools
+ import _collections_abc
+ @functools.wraps(func)
  def wrapped(*args, **kwargs):
  coro = func(*args, **kwargs)
  if (coro.__class__ is CoroutineType or

Lib/weakref.py

@@ -21,7 +21,7 @@
 
 from _weakrefset import WeakSet, _IterationGuard
 
-import collections.abc # Import after _weakref to avoid circular import.
+import _collections_abc # Import after _weakref to avoid circular import.
 import sys
 import itertools
 
@@ -87,7 +87,7 @@ def __ne__(self, other):
  __hash__ = ref.__hash__
 
 
-class WeakValueDictionary(collections.abc.MutableMapping):
+class WeakValueDictionary(_collections_abc.MutableMapping):
  """Mapping class that references values weakly.
 
  Entries in the dictionary will be discarded when no strong
@@ -340,7 +340,7 @@ def __init__(self, ob, callback, key):
  super().__init__(ob, callback)
 
 
-class WeakKeyDictionary(collections.abc.MutableMapping):
+class WeakKeyDictionary(_collections_abc.MutableMapping):
  """ Mapping class that references keys weakly.
 
  Entries in the dictionary will be discarded when there is no