diff --git a/Lib/ldap/asyncsearch.py b/Lib/ldap/asyncsearch.py
index 80b5b2a9..f9874d28 100644
--- a/Lib/ldap/asyncsearch.py
+++ b/Lib/ldap/asyncsearch.py
@@ -51,9 +51,9 @@ def __init__(self,l):
 
   def startSearch(
     self,
-    searchRoot,
-    searchScope,
-    filterStr,
+    searchRoot=None,
+    searchScope=None,
+    filterStr=None,
     attrList=None,
     attrsOnly=0,
     timeout=-1,
diff --git a/Lib/ldap/controls/openldap.py b/Lib/ldap/controls/openldap.py
index 5da2dd3f..58dafee0 100644
--- a/Lib/ldap/controls/openldap.py
+++ b/Lib/ldap/controls/openldap.py
@@ -51,7 +51,7 @@ class SearchNoOpMixIn:
   for easily using the no-op search control.
   """
 
-  def noop_search_st(self,base,scope=ldap.SCOPE_SUBTREE,filterstr='(objectClass=*)',timeout=-1):
+  def noop_search_st(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr='(objectClass=*)',timeout=-1):
     try:
       msg_id = self.search_ext(
         base,
diff --git a/Lib/ldap/functions.py b/Lib/ldap/functions.py
index 6c351eff..afcadd74 100644
--- a/Lib/ldap/functions.py
+++ b/Lib/ldap/functions.py
@@ -65,10 +65,11 @@ def _ldap_function_call(lock,func,*args,**kwargs):
   return result
 
 
-def initialize(uri,trace_level=0,trace_file=sys.stdout,trace_stack_limit=None, bytes_mode=None):
+def initialize(uri=None,trace_level=0,trace_file=sys.stdout,trace_stack_limit=None, bytes_mode=None):
   """
   Return LDAPObject instance by opening LDAP connection to
-  LDAP host specified by LDAP URL
+  LDAP host specified by LDAP URL. If uri is None, use the value
+  from ldap.conf/.ldaprc.
 
   Parameters:
   uri
diff --git a/Lib/ldap/ldapobject.py b/Lib/ldap/ldapobject.py
index 36bf034f..7ba29f6d 100644
--- a/Lib/ldap/ldapobject.py
+++ b/Lib/ldap/ldapobject.py
@@ -92,7 +92,7 @@ class SimpleLDAPObject:
   }
 
   def __init__(
-    self,uri,
+    self,uri=None,
     trace_level=0,trace_file=None,trace_stack_limit=5,bytes_mode=None,
     bytes_strictness=None,
   ):
@@ -769,13 +769,13 @@ def result4(self,msgid=ldap.RES_ANY,all=1,timeout=None,add_ctrls=0,add_intermedi
         resp_data = self._bytesify_results(resp_data, with_ctrls=add_ctrls)
     return resp_type, resp_data, resp_msgid, decoded_resp_ctrls, resp_name, resp_value
 
-  def search_ext(self,base,scope,filterstr=None,attrlist=None,attrsonly=0,serverctrls=None,clientctrls=None,timeout=-1,sizelimit=0):
+  def search_ext(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0,serverctrls=None,clientctrls=None,timeout=-1,sizelimit=0):
     """
-    search(base, scope [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0]]]) -> int
-    search_s(base, scope [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0]]])
-    search_st(base, scope [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0 [,timeout=-1]]]])
-    search_ext(base,scope,[,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0 [,serverctrls=None [,clientctrls=None [,timeout=-1 [,sizelimit=0]]]]]]])
-    search_ext_s(base,scope,[,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0 [,serverctrls=None [,clientctrls=None [,timeout=-1 [,sizelimit=0]]]]]]])
+    search([base=None, [scope=ldap.SCOPE_SUBTREE, [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0]]]]]) -> int
+    search_s([base=None, [scope=ldap.SCOPE_SUBTREE, [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0]]]]])
+    search_st([base=None, [scope=ldap.SCOPE_SUBTREE, [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0 [,timeout=-1]]]]]])
+    search_ext([base=None, [scope=ldap.SCOPE_SUBTREE, [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0 [,serverctrls=None [,clientctrls=None [,timeout=-1 [,sizelimit=0]]]]]]]]])
+    search_ext_s([base=None, [scope=ldap.SCOPE_SUBTREE, [,filterstr='(objectClass=*)' [,attrlist=None [,attrsonly=0 [,serverctrls=None [,clientctrls=None [,timeout=-1 [,sizelimit=0]]]]]]]]])
 
         Perform an LDAP search operation, with base as the DN of
         the entry at which to start the search, scope being one of
@@ -841,17 +841,17 @@ def search_ext(self,base,scope,filterstr=None,attrlist=None,attrsonly=0,serverct
       timeout,sizelimit,
     )
 
-  def search_ext_s(self,base,scope,filterstr=None,attrlist=None,attrsonly=0,serverctrls=None,clientctrls=None,timeout=-1,sizelimit=0):
+  def search_ext_s(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0,serverctrls=None,clientctrls=None,timeout=-1,sizelimit=0):
     msgid = self.search_ext(base,scope,filterstr,attrlist,attrsonly,serverctrls,clientctrls,timeout,sizelimit)
     return self.result(msgid,all=1,timeout=timeout)[1]
 
-  def search(self,base,scope,filterstr=None,attrlist=None,attrsonly=0):
+  def search(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0):
     return self.search_ext(base,scope,filterstr,attrlist,attrsonly,None,None)
 
-  def search_s(self,base,scope,filterstr=None,attrlist=None,attrsonly=0):
+  def search_s(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0):
     return self.search_ext_s(base,scope,filterstr,attrlist,attrsonly,None,None,timeout=self.timeout)
 
-  def search_st(self,base,scope,filterstr=None,attrlist=None,attrsonly=0,timeout=-1):
+  def search_st(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0,timeout=-1):
     return self.search_ext_s(base,scope,filterstr,attrlist,attrsonly,None,None,timeout)
 
   def start_tls_s(self):
@@ -962,7 +962,7 @@ def search_subschemasubentry_s(self,dn=None):
     except IndexError:
       return None
 
-  def read_s(self,dn,filterstr=None,attrlist=None,serverctrls=None,clientctrls=None,timeout=-1):
+  def read_s(self,dn=None,filterstr=None,attrlist=None,serverctrls=None,clientctrls=None,timeout=-1):
     """
     Reads and returns a single entry specified by `dn'.
 
@@ -1005,7 +1005,7 @@ def read_subschemasubentry_s(self,subschemasubentry_dn,attrs=None):
     else:
       return subschemasubentry
 
-  def find_unique_entry(self,base,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0,serverctrls=None,clientctrls=None,timeout=-1):
+  def find_unique_entry(self,base=None,scope=ldap.SCOPE_SUBTREE,filterstr=None,attrlist=None,attrsonly=0,serverctrls=None,clientctrls=None,timeout=-1):
     """
     Returns a unique entry, raises exception if not unique
     """
@@ -1077,7 +1077,7 @@ class ReconnectLDAPObject(SimpleLDAPObject):
   }
 
   def __init__(
-    self,uri,
+    self,uri=None,
     trace_level=0,trace_file=None,trace_stack_limit=5,bytes_mode=None,
     bytes_strictness=None, retry_max=1, retry_delay=60.0
   ):
diff --git a/Lib/ldap/syncrepl.py b/Lib/ldap/syncrepl.py
index 0de5cec4..660d0a30 100644
--- a/Lib/ldap/syncrepl.py
+++ b/Lib/ldap/syncrepl.py
@@ -349,7 +349,7 @@ class SyncreplConsumer:
     SyncreplConsumer - LDAP syncrepl consumer object.
     """
 
-    def syncrepl_search(self, base, scope, mode='refreshOnly', cookie=None, **search_args):
+    def syncrepl_search(self, base=None, scope=None, mode='refreshOnly', cookie=None, **search_args):
         """
         Starts syncrepl search operation.
 
diff --git a/Modules/LDAPObject.c b/Modules/LDAPObject.c
index 2bd6209c..9d33b93d 100644
--- a/Modules/LDAPObject.c
+++ b/Modules/LDAPObject.c
@@ -1250,7 +1250,7 @@ l_ldap_search_ext(LDAPObject *self, PyObject *args)
     int msgid;
     int ldaperror;
 
-    if (!PyArg_ParseTuple(args, "sis|OiOOdi:search_ext",
+    if (!PyArg_ParseTuple(args, "zis|OiOOdi:search_ext",
                           &base, &scope, &filter, &attrlist, &attrsonly,
                           &serverctrls, &clientctrls, &timeout, &sizelimit))
         return NULL;
diff --git a/Modules/functions.c b/Modules/functions.c
index 4731efb8..f7ef446f 100644
--- a/Modules/functions.c
+++ b/Modules/functions.c
@@ -16,7 +16,7 @@ l_ldap_initialize(PyObject *unused, PyObject *args)
     LDAP *ld = NULL;
     int ret;
 
-    if (!PyArg_ParseTuple(args, "s:initialize", &uri))
+    if (!PyArg_ParseTuple(args, "z:initialize", &uri))
         return NULL;
 
     Py_BEGIN_ALLOW_THREADS ret = ldap_initialize(&ld, uri);
diff --git a/Tests/t_ldapobject.py b/Tests/t_ldapobject.py
index 33c2c5a9..b586207c 100644
--- a/Tests/t_ldapobject.py
+++ b/Tests/t_ldapobject.py
@@ -117,7 +117,7 @@ def test_reject_bytes_base(self):
         elif sys.version_info >= (3, 5, 0):
             # Python 3.4.x does not include 'search_ext()' in message
             self.assertEqual(
-                "search_ext() argument 1 must be str, not bytes",
+                "search_ext() argument 1 must be str or None, not bytes",
                 text_type(e.exception)
             )