gh-118761: Improve import time by lazy import of traceback

Lib/_pyrepl/_threading_handler.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 from dataclasses import dataclass, field
-import traceback
 
 
 TYPE_CHECKING = False
@@ -55,6 +54,7 @@ def add(self, s: str) -> None:
                 self.messages.append(s)
 
         def exception(self, args: ExceptHookArgs) -> None:
+            import traceback
             lines = traceback.format_exception(
                 args.exc_type,
                 args.exc_value,

Lib/code.py

@@ -7,7 +7,6 @@
 
 import builtins
 import sys
-import traceback
 from codeop import CommandCompiler, compile_command
 
 __all__ = ["InteractiveInterpreter", "InteractiveConsole", "interact",
@@ -161,6 +160,7 @@ def _showtraceback(self, typ, value, tb, source):
     def _excepthook(self, typ, value, tb):
         # This method is being overwritten in
         # _pyrepl.console.InteractiveColoredConsole
+        import traceback
         lines = traceback.format_exception(typ, value, tb)
         self.write(''.join(lines))
 

Lib/doctest.py

@@ -100,7 +100,6 @@ def _test():
 import pdb
 import re
 import sys
-import traceback
 import unittest
 from io import StringIO, IncrementalNewlineDecoder
 from collections import namedtuple
@@ -273,6 +272,7 @@ def _exception_traceback(exc_info):
     # Get a traceback message.
     excout = StringIO()
     exc_type, exc_val, exc_tb = exc_info
+    import traceback
     traceback.print_exception(exc_type, exc_val, exc_tb, file=excout)
     return excout.getvalue()
 
@@ -1414,6 +1414,7 @@ def __run(self, test, compileflags, out):
 
             # The example raised an exception:  check if it was expected.
             else:
+                import traceback
                 formatted_ex = traceback.format_exception_only(*exception[:2])
                 if issubclass(exception[0], SyntaxError):
                     # SyntaxError / IndentationError is special:

Lib/logging/config.py

@@ -34,7 +34,6 @@
 import re
 import struct
 import threading
-import traceback
 
 from socketserver import ThreadingTCPServer, StreamRequestHandler
 
@@ -994,6 +993,7 @@ def handle(self):
                             try:
                                 fileConfig(file)
                             except Exception:
+                                import traceback
                                 traceback.print_exc()
                     if self.server.ready:
                         self.server.ready.set()

Lib/pdb.py

@@ -83,7 +83,6 @@
 import textwrap
 import tokenize
 import itertools
-import traceback
 import linecache
 import _colorize
 
@@ -219,6 +218,7 @@ def __init__(self, target):
             print(f"ImportError: {e}")
             sys.exit(1)
         except Exception:
+            import traceback
             traceback.print_exc()
             sys.exit(1)
 
@@ -257,6 +257,7 @@ def __init__(self, target):
             print(f"ImportError: {e}")
             sys.exit(1)
         except Exception:
+            import traceback
             traceback.print_exc()
             sys.exit(1)
 
@@ -2262,6 +2263,7 @@ def _run(self, target: _ExecutableTarget):
         self.run(target.code)
 
     def _format_exc(self, exc: BaseException):
+        import traceback
         return traceback.format_exception_only(exc)[-1].strip()
 
     def _compile_error_message(self, expr):
@@ -2531,6 +2533,7 @@ def main():
             print("The program exited via sys.exit(). Exit status:", end=' ')
             print(e)
         except BaseException as e:
+            import traceback
             traceback.print_exception(e, colorize=_colorize.can_colorize())
             print("Uncaught exception. Entering post mortem debugging")
             print("Running 'cont' or 'step' will restart the program")

Lib/py_compile.py

@@ -10,7 +10,6 @@
 import os
 import os.path
 import sys
-import traceback
 
 __all__ = ["compile", "main", "PyCompileError", "PycInvalidationMode"]
 
@@ -46,6 +45,7 @@ class PyCompileError(Exception):
     def __init__(self, exc_type, exc_value, file, msg=''):
         exc_type_name = exc_type.__name__
         if exc_type is SyntaxError:
+            import traceback
             tbtext = ''.join(traceback.format_exception_only(
                 exc_type, exc_value))
             errmsg = tbtext.replace('File "<string>"', 'File "%s"' % file)

Lib/pydoc.py

@@ -75,7 +75,6 @@ class or function within a module or module in a package.  If the
 from annotationlib import Format
 from collections import deque
 from reprlib import Repr
-from traceback import format_exception_only
 
 from _pyrepl.pager import (get_pager, pipe_pager,
                            plain_pager, tempfile_pager, tty_pager)
@@ -2628,6 +2627,7 @@ def html_getobj(url):
         return title, content
 
     def html_error(url, exc):
+        from traceback import format_exception_only
         heading = html.heading(
             '<strong class="title">Error</strong>',
         )

Lib/unittest/case.py

@@ -8,7 +8,6 @@
 import warnings
 import collections
 import contextlib
-import traceback
 import time
 import types
 
@@ -262,6 +261,7 @@ def __exit__(self, exc_type, exc_value, tb):
             else:
                 self._raiseFailure("{} not raised".format(exc_name))
         else:
+            import traceback
             traceback.clear_frames(tb)
         if not issubclass(exc_type, self.expected):
             # let unexpected exceptions pass through

Lib/unittest/loader.py

@@ -3,7 +3,6 @@
 import os
 import re
 import sys
-import traceback
 import types
 import functools
 
@@ -35,11 +34,13 @@ def testFailure():
 
 
 def _make_failed_import_test(name, suiteClass):
+    import traceback
     message = 'Failed to import test module: %s\n%s' % (
         name, traceback.format_exc())
     return _make_failed_test(name, ImportError(message), suiteClass, message)
 
 def _make_failed_load_tests(name, exception, suiteClass):
+    import traceback
     message = 'Failed to call load_tests:\n%s' % (traceback.format_exc(),)
     return _make_failed_test(
         name, exception, suiteClass, message)
@@ -163,6 +164,7 @@ def loadTestsFromName(self, name, module=None):
                     return error_case
                 else:
                     # Otherwise, we signal that an AttributeError has occurred.
+                    import traceback
                     error_case, error_message = _make_failed_test(
                         part, e, self.suiteClass,
                         'Failed to access attribute:\n%s' % (

Lib/unittest/result.py

@@ -2,7 +2,6 @@
 
 import io
 import sys
-import traceback
 
 from . import util
 from functools import wraps
@@ -186,6 +185,7 @@ def _exc_info_to_string(self, err, test):
         """Converts a sys.exc_info()-style tuple of values into a string."""
         exctype, value, tb = err
         tb = self._clean_tracebacks(exctype, value, tb, test)
+        import traceback
         tb_e = traceback.TracebackException(
             exctype, value, tb,
             capture_locals=self.tb_locals, compact=True)

Lib/xmlrpc/server.py

@@ -115,11 +115,7 @@ def export_add(self, x, y):
 import os
 import re
 import pydoc
-import traceback
-try:
-    import fcntl
-except ImportError:
-    fcntl = None
+
 
 def resolve_dotted_attribute(obj, attr, allow_dotted_names=True):
     """resolve_dotted_attribute(a, 'b.c.d') => a.b.c.d
@@ -512,6 +508,7 @@ def do_POST(self):
             if hasattr(self.server, '_send_traceback_header') and \
                     self.server._send_traceback_header:
                 self.send_header("X-exception", str(e))
+                import traceback
                 trace = traceback.format_exc()
                 trace = str(trace.encode('ASCII', 'backslashreplace'), 'ASCII')
                 self.send_header("X-traceback", trace)

Misc/NEWS.d/next/Library/2025-02-07-17-04-08.gh-issue-118761.hkNOEA.rst

@@ -0,0 +1,2 @@
+Improve import time of various stdlib modules by lazy import ``traceback``.
+Patch by Semyon Moroz.