Add the comments explaining imports inside functions.

python · serhiy-storchaka · Sep 25, 2017 · Apr 24, 2017 · Apr 26, 2017 · Apr 26, 2017
commit d8a622c6cf4d0f52d257052152a3a20485cd1d25
diff --git a/Lib/argparse.py b/Lib/argparse.py
@@ -608,6 +608,8 @@ def _iter_indented_subactions(self, action):
 
     def _split_lines(self, text, width):
         text = self._whitespace_matcher.sub(' ', text).strip()
+        # 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)
 
@@ -948,6 +950,9 @@ def __call__(self, parser, namespace, values, option_string=None):
         if items is None:
             items = []
         else:
+            # The copy module is used only in the 'append' and 'append_const'
+            # actions.  Delay its import for speeding up the case when they
+            # are not used.
             import copy
             items = copy.copy(items)
         items.append(values)

diff --git a/Lib/gettext.py b/Lib/gettext.py
@@ -335,6 +335,8 @@ def _get_versions(self, version):
 
     def _parse(self, fp):
         """Override this method to support alternative .mo formats."""
+        # 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
@@ -526,6 +528,8 @@ 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:

diff --git a/Lib/types.py b/Lib/types.py
@@ -244,6 +244,7 @@ def coroutine(func):
     # return generator-like objects (for instance generators
     # compiled with Cython).
 
+    # Delay functools and _collections_abc import for speeding up types import.
     import functools
     import _collections_abc
     @functools.wraps(func)