Update NEWS, docs, and patchlevel for 3.7.0b2
diff --git a/Lib/pydoc_data/topics.py b/Lib/pydoc_data/topics.py
index a979931..ede9385 100644
--- a/Lib/pydoc_data/topics.py
+++ b/Lib/pydoc_data/topics.py
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Autogenerated by Sphinx on Tue Jan 30 18:36:07 2018
+# Autogenerated by Sphinx on Tue Feb 27 19:39:14 2018
 topics = {'assert': 'The "assert" statement\n'
            '**********************\n'
            '\n'
@@ -483,15 +483,19 @@
                      '\n'
                      'object.__getattr__(self, name)\n'
                      '\n'
-                     '   Called when an attribute lookup has not found the '
-                     'attribute in the\n'
-                     '   usual places (i.e. it is not an instance attribute '
-                     'nor is it found\n'
-                     '   in the class tree for "self").  "name" is the '
-                     'attribute name. This\n'
-                     '   method should return the (computed) attribute value '
-                     'or raise an\n'
-                     '   "AttributeError" exception.\n'
+                     '   Called when the default attribute access fails with '
+                     'an\n'
+                     '   "AttributeError" (either "__getattribute__()" raises '
+                     'an\n'
+                     '   "AttributeError" because *name* is not an instance '
+                     'attribute or an\n'
+                     '   attribute in the class tree for "self"; or '
+                     '"__get__()" of a *name*\n'
+                     '   property raises "AttributeError").  This method '
+                     'should either\n'
+                     '   return the (computed) attribute value or raise an '
+                     '"AttributeError"\n'
+                     '   exception.\n'
                      '\n'
                      '   Note that if the attribute is found through the '
                      'normal mechanism,\n'
@@ -4718,9 +4722,9 @@
                   'conversion] [":" format_spec] "}"\n'
                   '      field_name        ::= arg_name ("." attribute_name | '
                   '"[" element_index "]")*\n'
-                  '      arg_name          ::= [identifier | integer]\n'
+                  '      arg_name          ::= [identifier | digit+]\n'
                   '      attribute_name    ::= identifier\n'
-                  '      element_index     ::= integer | index_string\n'
+                  '      element_index     ::= digit+ | index_string\n'
                   '      index_string      ::= <any source character except '
                   '"]"> +\n'
                   '      conversion        ::= "r" | "s" | "a"\n'
@@ -4879,9 +4883,9 @@
                   '   fill            ::= <any character>\n'
                   '   align           ::= "<" | ">" | "=" | "^"\n'
                   '   sign            ::= "+" | "-" | " "\n'
-                  '   width           ::= integer\n'
+                  '   width           ::= digit+\n'
                   '   grouping_option ::= "_" | ","\n'
-                  '   precision       ::= integer\n'
+                  '   precision       ::= digit+\n'
                   '   type            ::= "b" | "c" | "d" | "e" | "E" | "f" | '
                   '"F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"\n'
                   '\n'
@@ -8057,15 +8061,17 @@
                  '\n'
                  'object.__getattr__(self, name)\n'
                  '\n'
-                 '   Called when an attribute lookup has not found the '
-                 'attribute in the\n'
-                 '   usual places (i.e. it is not an instance attribute nor is '
-                 'it found\n'
-                 '   in the class tree for "self").  "name" is the attribute '
-                 'name. This\n'
-                 '   method should return the (computed) attribute value or '
-                 'raise an\n'
-                 '   "AttributeError" exception.\n'
+                 '   Called when the default attribute access fails with an\n'
+                 '   "AttributeError" (either "__getattribute__()" raises an\n'
+                 '   "AttributeError" because *name* is not an instance '
+                 'attribute or an\n'
+                 '   attribute in the class tree for "self"; or "__get__()" of '
+                 'a *name*\n'
+                 '   property raises "AttributeError").  This method should '
+                 'either\n'
+                 '   return the (computed) attribute value or raise an '
+                 '"AttributeError"\n'
+                 '   exception.\n'
                  '\n'
                  '   Note that if the attribute is found through the normal '
                  'mechanism,\n'
@@ -11599,7 +11605,9 @@
           '\n'
           '   Frame objects\n'
           '      Frame objects represent execution frames.  They may occur in\n'
-          '      traceback objects (see below).\n'
+          '      traceback objects (see below), and are also passed to '
+          'registered\n'
+          '      trace functions.\n'
           '\n'
           '      Special read-only attributes: "f_back" is to the previous '
           'stack\n'
@@ -11654,44 +11662,59 @@
           '         New in version 3.4.\n'
           '\n'
           '   Traceback objects\n'
-          '      Traceback objects represent a stack trace of an exception.  '
-          'A\n'
-          '      traceback object is created when an exception occurs.  When '
-          'the\n'
-          '      search for an exception handler unwinds the execution stack, '
-          'at\n'
-          '      each unwound level a traceback object is inserted in front '
-          'of\n'
-          '      the current traceback.  When an exception handler is '
-          'entered,\n'
-          '      the stack trace is made available to the program. (See '
-          'section\n'
-          '      The try statement.) It is accessible as the third item of '
-          'the\n'
-          '      tuple returned by "sys.exc_info()". When the program contains '
-          'no\n'
-          '      suitable handler, the stack trace is written (nicely '
-          'formatted)\n'
-          '      to the standard error stream; if the interpreter is '
-          'interactive,\n'
-          '      it is also made available to the user as '
-          '"sys.last_traceback".\n'
+          '         Traceback objects represent a stack trace of an '
+          'exception.  A\n'
+          '         traceback object is implicitly created when an exception\n'
+          '         occurs, and may also be explicitly created by calling\n'
+          '         "types.TracebackType".\n'
           '\n'
-          '      Special read-only attributes: "tb_next" is the next level in '
+          '         For implicitly created tracebacks, when the search for an\n'
+          '         exception handler unwinds the execution stack, at each\n'
+          '         unwound level a traceback object is inserted in front of '
           'the\n'
-          '      stack trace (towards the frame where the exception occurred), '
-          'or\n'
-          '      "None" if there is no next level; "tb_frame" points to the\n'
-          '      execution frame of the current level; "tb_lineno" gives the '
-          'line\n'
-          '      number where the exception occurred; "tb_lasti" indicates '
+          '         current traceback.  When an exception handler is entered, '
           'the\n'
-          '      precise instruction.  The line number and last instruction '
+          '         stack trace is made available to the program. (See '
+          'section\n'
+          '         The try statement.) It is accessible as the third item of '
+          'the\n'
+          '         tuple returned by "sys.exc_info()", and as the\n'
+          '         "__traceback__" attribute of the caught exception.\n'
+          '\n'
+          '         When the program contains no suitable handler, the stack\n'
+          '         trace is written (nicely formatted) to the standard error\n'
+          '         stream; if the interpreter is interactive, it is also '
+          'made\n'
+          '         available to the user as "sys.last_traceback".\n'
+          '\n'
+          '         For explicitly created tracebacks, it is up to the creator '
+          'of\n'
+          '         the traceback to determine how the "tb_next" attributes\n'
+          '         should be linked to form a full stack trace.\n'
+          '\n'
+          '         Special read-only attributes: "tb_frame" points to the\n'
+          '         execution frame of the current level; "tb_lineno" gives '
+          'the\n'
+          '         line number where the exception occurred; "tb_lasti"\n'
+          '         indicates the precise instruction. The line number and '
+          'last\n'
+          '         instruction in the traceback may differ from the line '
+          'number\n'
+          '         of its frame object if the exception occurred in a "try"\n'
+          '         statement with no matching except clause or with a '
+          'finally\n'
+          '         clause.\n'
+          '\n'
+          '         Special writable attribute: "tb_next" is the next level '
           'in\n'
-          '      the traceback may differ from the line number of its frame\n'
-          '      object if the exception occurred in a "try" statement with '
-          'no\n'
-          '      matching except clause or with a finally clause.\n'
+          '         the stack trace (towards the frame where the exception\n'
+          '         occurred), or "None" if there is no next level.\n'
+          '\n'
+          '      Changed in version 3.7: Traceback objects can now be '
+          'explicitly\n'
+          '      instantiated from Python code, and the "tb_next" attribute '
+          'of\n'
+          '      existing instances can be updated.\n'
           '\n'
           '   Slice objects\n'
           '      Slice objects are used to represent slices for '