diff --git a/contrib/perf.py b/contrib/perf.py
--- a/contrib/perf.py
+++ b/contrib/perf.py
@@ -40,6 +40,7 @@
     util,
 )
 
+
 # for "historical portability":
 # try to import modules separately (in dict order), and ignore
 # failure, because these aren't available with early Mercurial
@@ -64,6 +65,12 @@
     from mercurial import scmutil # since 1.9 (or 8b252e826c68)
 except ImportError:
     pass
+try:
+    from mercurial import pycompat
+    getargspec = pycompat.getargspec  # added to module after 4.5
+except (ImportError, AttributeError):
+    import inspect
+    getargspec = inspect.getargspec
 
 # for "historical portability":
 # define util.safehasattr forcibly, because util.safehasattr has been
@@ -114,9 +121,8 @@
 if safehasattr(registrar, 'command'):
     command = registrar.command(cmdtable)
 elif safehasattr(cmdutil, 'command'):
-    import inspect
     command = cmdutil.command(cmdtable)
-    if 'norepo' not in inspect.getargspec(command)[0]:
+    if 'norepo' not in getargspec(command).args:
         # for "historical portability":
         # wrap original cmdutil.command, because "norepo" option has
         # been available since 3.1 (or 75a96326cecb)
diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -195,11 +195,7 @@
             try:
                 extsetup(ui)
             except TypeError:
-                # Try to use getfullargspec (Python 3) first, and fall
-                # back to getargspec only if it doesn't exist so as to
-                # avoid warnings.
-                if getattr(inspect, 'getfullargspec',
-                           getattr(inspect, 'getargspec'))(extsetup).args:
+                if pycompat.getargspec(extsetup).args:
                     raise
                 extsetup() # old extsetup with no ui argument
         except Exception as inst:
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -9,7 +9,6 @@
 
 import errno
 import hashlib
-import inspect
 import os
 import random
 import time
@@ -1068,7 +1067,7 @@
                 if not fn:
                     fn = lambda s, c, **kwargs: util.filter(s, c)
                 # Wrap old filters not supporting keyword arguments
-                if not inspect.getargspec(fn)[2]:
+                if not pycompat.getargspec(fn)[2]:
                     oldfn = fn
                     fn = lambda s, c, **kwargs: oldfn(s, c)
                 l.append((mf, fn, params))
diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -11,6 +11,7 @@
 from __future__ import absolute_import
 
 import getopt
+import inspect
 import os
 import shlex
 import sys
@@ -65,6 +66,7 @@
     maplist = lambda *args: list(map(*args))
     ziplist = lambda *args: list(zip(*args))
     rawinput = input
+    getargspec = inspect.getfullargspec
 
     # TODO: .buffer might not exist if std streams were replaced; we'll need
     # a silly wrapper to make a bytes stream backed by a unicode one.
@@ -330,6 +332,8 @@
     maplist = map
     ziplist = zip
     rawinput = raw_input
+    getargspec = inspect.getargspec
+
 
     def emailparser(*args, **kwargs):
         import email.parser