diff --git a/Lib/csv.py b/Lib/csv.py
index 2f38bb1a1..77f30c8d2 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -4,17 +4,22 @@ csv.py - read/write/investigate CSV files
 """
 
 import re
-from _csv import Error, writer, reader, \
+import types
+from _csv import Error, __version__, writer, reader, register_dialect, \
+                 unregister_dialect, get_dialect, list_dialects, \
+                 field_size_limit, \
                  QUOTE_MINIMAL, QUOTE_ALL, QUOTE_NONNUMERIC, QUOTE_NONE, \
+                 QUOTE_STRINGS, QUOTE_NOTNULL, \
                  __doc__
+from _csv import Dialect as _Dialect
 
-from collections import OrderedDict
 from io import StringIO
 
 __all__ = ["QUOTE_MINIMAL", "QUOTE_ALL", "QUOTE_NONNUMERIC", "QUOTE_NONE",
+           "QUOTE_STRINGS", "QUOTE_NOTNULL",
            "Error", "Dialect", "__doc__", "excel", "excel_tab",
            "field_size_limit", "reader", "writer",
-           "Sniffer",
+           "register_dialect", "get_dialect", "list_dialects", "Sniffer",
            "unregister_dialect", "__version__", "DictReader", "DictWriter",
            "unix_dialect"]
 
@@ -57,10 +62,12 @@ class excel(Dialect):
     skipinitialspace = False
     lineterminator = '\r\n'
     quoting = QUOTE_MINIMAL
+register_dialect("excel", excel)
 
 class excel_tab(excel):
     """Describe the usual properties of Excel-generated TAB-delimited files."""
     delimiter = '\t'
+register_dialect("excel-tab", excel_tab)
 
 class unix_dialect(Dialect):
     """Describe the usual properties of Unix-generated CSV files."""
@@ -70,11 +77,14 @@ class unix_dialect(Dialect):
     skipinitialspace = False
     lineterminator = '\n'
     quoting = QUOTE_ALL
+register_dialect("unix", unix_dialect)
 
 
 class DictReader:
     def __init__(self, f, fieldnames=None, restkey=None, restval=None,
                  dialect="excel", *args, **kwds):
+        if fieldnames is not None and iter(fieldnames) is fieldnames:
+            fieldnames = list(fieldnames)
         self._fieldnames = fieldnames   # list of keys for the dict
         self.restkey = restkey          # key to catch long rows
         self.restval = restval          # default value for short rows
@@ -111,7 +121,7 @@ class DictReader:
         # values
         while row == []:
             row = next(self.reader)
-        d = OrderedDict(zip(self.fieldnames, row))
+        d = dict(zip(self.fieldnames, row))
         lf = len(self.fieldnames)
         lr = len(row)
         if lf < lr:
@@ -121,13 +131,18 @@ class DictReader:
                 d[key] = self.restval
         return d
 
+    __class_getitem__ = classmethod(types.GenericAlias)
+
 
 class DictWriter:
     def __init__(self, f, fieldnames, restval="", extrasaction="raise",
                  dialect="excel", *args, **kwds):
+        if fieldnames is not None and iter(fieldnames) is fieldnames:
+            fieldnames = list(fieldnames)
         self.fieldnames = fieldnames    # list of keys for the dict
         self.restval = restval          # for writing short dicts
-        if extrasaction.lower() not in ("raise", "ignore"):
+        extrasaction = extrasaction.lower()
+        if extrasaction not in ("raise", "ignore"):
             raise ValueError("extrasaction (%s) must be 'raise' or 'ignore'"
                              % extrasaction)
         self.extrasaction = extrasaction
@@ -135,7 +150,7 @@ class DictWriter:
 
     def writeheader(self):
         header = dict(zip(self.fieldnames, self.fieldnames))
-        self.writerow(header)
+        return self.writerow(header)
 
     def _dict_to_list(self, rowdict):
         if self.extrasaction == "raise":
@@ -151,11 +166,8 @@ class DictWriter:
     def writerows(self, rowdicts):
         return self.writer.writerows(map(self._dict_to_list, rowdicts))
 
-# Guard Sniffer's type checking against builds that exclude complex()
-try:
-    complex
-except NameError:
-    complex = float
+    __class_getitem__ = classmethod(types.GenericAlias)
+
 
 class Sniffer:
     '''
@@ -404,14 +416,10 @@ class Sniffer:
                 continue # skip rows that have irregular number of columns
 
             for col in list(columnTypes.keys()):
-
-                for thisType in [int, float, complex]:
-                    try:
-                        thisType(row[col])
-                        break
-                    except (ValueError, OverflowError):
-                        pass
-                else:
+                thisType = complex
+                try:
+                    thisType(row[col])
+                except (ValueError, OverflowError):
                     # fallback to length of string
                     thisType = len(row[col])
 
@@ -427,7 +435,7 @@ class Sniffer:
         # on whether it's a header
         hasHeader = 0
         for col, colType in columnTypes.items():
-            if type(colType) == type(0): # it's a length
+            if isinstance(colType, int): # it's a length
                 if len(header[col]) != colType:
                     hasHeader += 1
                 else: