diff -r a4515186bf9c Lib/locale.py
--- a/Lib/locale.py	Fri Oct 11 12:09:51 2013 -0400
+++ b/Lib/locale.py	Fri Oct 11 22:10:08 2013 +0200
@@ -14,8 +14,7 @@
 import sys
 import encodings
 import encodings.aliases
-import re
-import collections
+from collections.abc import Mapping
 from builtins import str as _builtin_str
 import functools
 
@@ -178,8 +177,9 @@
         amount -= 1
     return s[lpos:rpos+1]
 
-_percent_re = re.compile(r'%(?:\((?P<key>.*?)\))?'
-                         r'(?P<modifiers>[-#0-9 +*.hlL]*?)[eEfFgGdiouxXcrs%]')
+# Compilation of _percent_re is delayed to reduce startup time.
+_percent_re = (r'%(?:\((?P<key>.*?)\))?'
+               r'(?P<modifiers>[-#0-9 +*.hlL]*?)[eEfFgGdiouxXcrs%]')
 
 def format(percent, value, grouping=False, monetary=False, *additional):
     """Returns the locale-aware substitution of a %? specifier
@@ -187,6 +187,10 @@
 
     additional is for format strings which contain one or more
     '*' modifiers."""
+    global _percent_re
+    if isinstance(_percent_re, str):
+        import re
+        _percent_re = re.compile(_percent_re)
     # this is only for one-percent-specifier strings and this should be checked
     match = _percent_re.match(percent)
     if not match or len(match.group())!= len(percent):
@@ -222,10 +226,14 @@
     """Formats a string in the same way that the % formatting would use,
     but takes the current locale into account.
     Grouping is applied if the third parameter is true."""
+    global _percent_re
+    if isinstance(_percent_re, str):
+        import re
+        _percent_re = re.compile(_percent_re)
     percents = list(_percent_re.finditer(f))
     new_f = _percent_re.sub('%s', f)
 
-    if isinstance(val, collections.Mapping):
+    if isinstance(val, Mapping):
         new_val = []
         for perc in percents:
             if perc.group()[-1]=='%':
diff -r a4515186bf9c Lib/site.py
--- a/Lib/site.py	Fri Oct 11 12:09:51 2013 -0400
+++ b/Lib/site.py	Fri Oct 11 22:10:08 2013 +0200
@@ -70,7 +70,6 @@
 
 import sys
 import os
-import re
 import builtins
 import _sitebuiltins
 
@@ -436,11 +435,10 @@
                 encodings._cache[enc] = encodings._unknown
                 encodings.aliases.aliases[enc] = 'mbcs'
 
-
-CONFIG_LINE = re.compile(r'^(?P<key>(\w|[-_])+)\s*=\s*(?P<value>.*)\s*$')
+CONFIG_LINE = None
 
 def venv(known_paths):
-    global PREFIXES, ENABLE_USER_SITE
+    global PREFIXES, ENABLE_USER_SITE, CONFIG_LINE
 
     env = os.environ
     if sys.platform == 'darwin' and '__PYVENV_LAUNCHER__' in env:
@@ -460,6 +458,10 @@
         ]
 
     if candidate_confs:
+        if CONFIG_LINE is None:
+            import re
+            CONFIG_LINE = re.compile(r'^(?P<key>(\w|[-_])+)\s*'
+                                     r'=\s*(?P<value>.*)\s*$')
         virtual_conf = candidate_confs[0]
         system_site = "true"
         with open(virtual_conf) as f:
diff -r a4515186bf9c Lib/sysconfig.py
--- a/Lib/sysconfig.py	Fri Oct 11 12:09:51 2013 -0400
+++ b/Lib/sysconfig.py	Fri Oct 11 22:10:08 2013 +0200
@@ -1,7 +1,6 @@
 """Access to Python's configuration information."""
 
 import os
-import re
 import sys
 from os.path import pardir, realpath
 
@@ -222,6 +221,7 @@
     """
     # Regexes needed for parsing Makefile (and similar syntaxes,
     # like old-style Setup files).
+    import re
     _variable_rx = re.compile("([a-zA-Z][a-zA-Z0-9_]+)\s*=\s*(.*)")
     _findvar1_rx = re.compile(r"\$\(([A-Za-z][A-Za-z0-9_]*)\)")
     _findvar2_rx = re.compile(r"\${([A-Za-z][A-Za-z0-9_]*)}")
@@ -435,6 +435,7 @@
     """
     if vars is None:
         vars = {}
+    import re
     define_rx = re.compile("#define ([A-Z][A-Za-z0-9_]+) (.*)\n")
     undef_rx = re.compile("/[*] #undef ([A-Z][A-Za-z0-9_]+) [*]/\n")
 
@@ -658,6 +659,7 @@
         return "%s-%s.%s" % (osname, version, release)
     elif osname[:6] == "cygwin":
         osname = "cygwin"
+        import re
         rel_re = re.compile(r'[\d.]+')
         m = rel_re.match(release)
         if m:
diff -r a4515186bf9c Lib/test/test_site.py
--- a/Lib/test/test_site.py	Fri Oct 11 12:09:51 2013 -0400
+++ b/Lib/test/test_site.py	Fri Oct 11 22:10:08 2013 +0200
@@ -18,6 +18,7 @@
 import subprocess
 import sysconfig
 from copy import copy
+import ast
 
 # Need to make sure to not import 'site' if someone specified ``-S`` at the
 # command-line.  Detect this by just making sure 'site' has not been imported
@@ -420,5 +421,19 @@
         self.assertEqual(code, 200, msg="Can't find " + url)
 
 
+class StartupImportTests(unittest.TestCase):
+
+    def test_startup_imports(self):
+        # This tests checks which modules are loaded by Python when it
+        # initially starts upon startup.
+        args = [sys.executable, '-I', '-c',
+                'import sys; print(sorted(sys.modules))']
+        stdout = subprocess.check_output(args).decode('utf-8')
+        modules = set(ast.literal_eval(stdout))
+
+        re_mods = {'re', '_sre', 'sre_compile', 'sre_constants', 'sre_parse'}
+        self.assertFalse(modules.intersection(re_mods))
+
+
 if __name__ == "__main__":
     unittest.main()