gh-143409: Use dict and set comprehensions when possible

.gitignore

@@ -159,6 +159,8 @@ Tools/msi/obj
 Tools/ssl/amd64
 Tools/ssl/win32
 Tools/freeze/test/outdir
+/.project
+/.pydevproject
 
 # The frozen modules are always generated by the build so we don't
 # keep them in the repo.  Also see Tools/build/freeze_modules.py.

Lib/_compat_pickle.py

@@ -161,9 +161,9 @@
     NAME_MAPPING[("multiprocessing", excname)] = ("multiprocessing.context", excname)
 
 # Same, but for 3.x to 2.x
-REVERSE_IMPORT_MAPPING = dict((v, k) for (k, v) in IMPORT_MAPPING.items())
+REVERSE_IMPORT_MAPPING = {v: k for (k, v) in IMPORT_MAPPING.items()}
 assert len(REVERSE_IMPORT_MAPPING) == len(IMPORT_MAPPING)
-REVERSE_NAME_MAPPING = dict((v, k) for (k, v) in NAME_MAPPING.items())
+REVERSE_NAME_MAPPING = {v: k for (k, v) in NAME_MAPPING.items()}
 assert len(REVERSE_NAME_MAPPING) == len(NAME_MAPPING)
 
 # Non-mutual mappings.

Lib/_pydecimal.py

@@ -3891,14 +3891,14 @@ def __init__(self, prec=None, rounding=None, Emin=None, Emax=None,
         if traps is None:
             self.traps = dc.traps.copy()
         elif not isinstance(traps, dict):
-            self.traps = dict((s, int(s in traps)) for s in _signals + traps)
+            self.traps = {s: int(s in traps) for s in _signals + traps}
         else:
             self.traps = traps
 
         if flags is None:
             self.flags = dict.fromkeys(_signals, 0)
         elif not isinstance(flags, dict):
-            self.flags = dict((s, int(s in flags)) for s in _signals + flags)
+            self.flags = {s: int(s in flags) for s in _signals + flags}
         else:
             self.flags = flags
 

Lib/cmd.py

@@ -295,8 +295,8 @@ def get_names(self):
 
     def complete_help(self, *args):
         commands = set(self.completenames(*args))
-        topics = set(a[5:] for a in self.get_names()
-                     if a.startswith('help_' + args[0]))
+        topics = {a[5:] for a in self.get_names()
+                  if a.startswith('help_' + args[0])}
         return list(commands | topics)
 
     def do_help(self, arg):

Lib/enum.py

@@ -1985,7 +1985,7 @@ def __call__(self, enumeration):
                     raise ValueError('aliases found in %r: %s' %
                             (enumeration, alias_details))
             elif check is CONTINUOUS:
-                values = set(e.value for e in enumeration)
+                values = {e.value for e in enumeration}
                 if len(values) < 2:
                     continue
                 low, high = min(values), max(values)

Lib/logging/__init__.py

@@ -1809,9 +1809,9 @@ def _hierlevel(logger):
             # exclude PlaceHolders - the last check is to ensure that lower-level
             # descendants aren't returned - if there are placeholders, a logger's
             # parent field might point to a grandparent or ancestor thereof.
-            return set(item for item in d.values()
+            return {item for item in d.values()
                        if isinstance(item, Logger) and item.parent is self and
-                       _hierlevel(item) == 1 + _hierlevel(item.parent))
+                       _hierlevel(item) == 1 + _hierlevel(item.parent)}
 
     def __repr__(self):
         level = getLevelName(self.getEffectiveLevel())

Lib/signal.py

@@ -69,7 +69,7 @@ def getsignal(signalnum):
     @_wraps(_signal.pthread_sigmask)
     def pthread_sigmask(how, mask):
         sigs_set = _signal.pthread_sigmask(how, mask)
-        return set(_int_to_enum(x, Signals) for x in sigs_set)
+        return {_int_to_enum(x, Signals) for x in sigs_set}
 
 
 if 'sigpending' in _globals:

Misc/ACKS

@@ -1931,6 +1931,7 @@ James Tocknell
 Bennett Todd
 R Lindsay Todd
 Eugene Toder
+Heikki Toivonen
 Erik Tollerud
 Stephen Tonkin
 Matias Torchinsky

Misc/NEWS.d/next/Library/2026-01-03-20-49-09.gh-issue-143409.vAsfk2.rst

@@ -0,0 +1 @@
+Use dict and set comprehensions when possible