gh-118761: Optimise import time for shlex

Lib/shlex.py

@@ -7,11 +7,7 @@
 # iterator interface by Gustavo Niemeyer, April 2003.
 # changes to tokenize more like Posix shells by Vinay Sajip, July 2016.
 
-import os
-import re
 import sys
-from collections import deque
-
 from io import StringIO
 
 __all__ = ["shlex", "split", "quote", "join"]
@@ -20,6 +16,8 @@ class shlex:
     "A lexical analyzer class for simple shell-like syntaxes."
     def __init__(self, instream=None, infile=None, posix=False,
                  punctuation_chars=False):
+        from collections import deque  # deferred import for performance
+
         if isinstance(instream, str):
             instream = StringIO(instream)
         if instream is not None:
@@ -278,6 +276,7 @@ def read_token(self):
 
     def sourcehook(self, newfile):
         "Hook called on a filename to be sourced."
+        import os.path
         if newfile[0] == '"':
             newfile = newfile[1:-1]
         # This implements cpp-like semantics for relative-path inclusion.
@@ -318,7 +317,14 @@ def join(split_command):
     return ' '.join(quote(arg) for arg in split_command)
 
 
-_find_unsafe = re.compile(r'[^\w@%+=:,./-]', re.ASCII).search
+def _find_unsafe(s, /):
+    # this function replaces itself with the compiled pattern on execution,
+    # to allow as deferred import of re for performance
+    global _find_unsafe
+    import re
+    _find_unsafe = re.compile(r'[^\w@%+=:,./-]', re.ASCII).search
+    return _find_unsafe(s)
+
 
 def quote(s):
     """Return a shell-escaped version of the string *s*."""

Misc/NEWS.d/next/Library/2025-04-03-00-56-48.gh-issue-118761.Vb0S1B.rst

@@ -0,0 +1,2 @@
+Improve import times by up to 33x for the :mod:`shlex` module. Patch by Adam
+Turner.