Issue #18219: Optimize csv.DictWriter for large number of columns.

Patch by Mariatta Wijaya.

diff --cc Misc/NEWS
index 20e4979add529fdca6955d23a78647f2ae3d9c12,237c9288e6c93f01411f595c7a5396edf7adfab0..2e4e1c9c37d379aa802f4b2f1cb2ac651523d1ba
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -88,36 -128,6 +88,39 @@@ Core and Builtin
  Library
  -------
  
++- Issue #18219: Optimize csv.DictWriter for large number of columns.
++  Patch by Mariatta Wijaya.
++
 +- Issue #28448: Fix C implemented asyncio.Future didn't work on Windows.
 +
 +- Issue #23214: In the "io" module, the argument to BufferedReader and
 +  BytesIO's read1() methods is now optional and can be -1, matching the
 +  BufferedIOBase specification.
 +
 +- Issue #28480: Fix error building socket module when multithreading is
 +  disabled.
 +
 +- Issue #28240: timeit: remove ``-c/--clock`` and ``-t/--time`` command line
 +  options which were deprecated since Python 3.3.
 +
 +- Issue #28240: timeit now repeats the benchmarks 5 times instead of only 3
 +  to make benchmarks more reliable.
 +
 +- Issue #28240: timeit autorange now uses a single loop iteration if the
 +  benchmark takes less than 10 seconds, instead of 10 iterations.
 +  "python3 -m timeit -s 'import time' 'time.sleep(1)'" now takes 4 seconds
 +  instead of 40 seconds.
 +
 +- Distutils.sdist now looks for README and setup.py files with case
 +  sensitivity. This behavior matches that found in Setuptools 6.0 and
 +  later. See `setuptools 100
 +  <https://github.com/pypa/setuptools/issues/100>`_ for rationale.
 +
 +- Issue #24452: Make webbrowser support Chrome on Mac OS X.
 +
 +- Issue #20766: Fix references leaked by pdb in the handling of SIGINT
 +  handlers.
 +
  - Issue #27998: Fixed bytes path support in os.scandir() on Windows.
    Patch by Eryk Sun.