Take Thomas comments into account

docs/source/whatsnew/pr/do_where.rst

@@ -1,2 +1,3 b''
 IPython debugger (IPdb) now supports the number of context lines for the
 ``where`` (and ``w``) commands. The `context` keyword is also available in various APIs.
+See PR #9097

tools/update_whatsnew.py

@@ -1,80 +1,78 b''
 #!/usr/bin/env python
 """Update the What's New doc (development version)
 
 This collects the snippets from whatsnew/pr/, moves their content into
 whatsnew/development.rst (chronologically ordered), and deletes the snippets.
 """
 
 import io
 import os
 from glob import glob
 from os.path import dirname, basename, abspath, join as pjoin
 from subprocess import check_call, check_output
 
 repo_root = dirname(dirname(abspath(__file__)))
 whatsnew_dir = pjoin(repo_root, 'docs', 'source', 'whatsnew')
 pr_dir = pjoin(whatsnew_dir, 'pr')
 target = pjoin(whatsnew_dir, 'development.rst')
 
 FEATURE_MARK = ".. DO NOT EDIT THIS LINE BEFORE RELEASE. FEATURE INSERTION POINT."
 INCOMPAT_MARK = ".. DO NOT EDIT THIS LINE BEFORE RELEASE. INCOMPAT INSERTION POINT."
 
 # 1. Collect the whatsnew snippet files ---------------------------------------
 
-files = set()
-for f in glob(pjoin(pr_dir, '*.rst')):
-    files.add(f)
+files = set(glob(pjoin(pr_dir, '*.rst')))
 # Ignore explanatory and example files
-files.difference_update({pjoin(pr_dir, f) for f in {'README.md',
+files.difference_update({pjoin(pr_dir, f) for f in {
                          'incompat-switching-to-perl.rst',
                          'antigravity-feature.rst'}
                          })
 
 
 def getmtime(f):
     return check_output(['git', 'log', '-1', '--format="%ai"', '--', f])
 
 files = sorted(files, key=getmtime)
 
 features, incompats = [], []
 for path in files:
     with io.open(path, encoding='utf-8') as f:
         try:
             content = f.read().rstrip()
         except Exception as e:
-            raise Exception('Error reading "{}"'.format(f))
+            raise Exception('Error reading "{}"'.format(f)) from e
 
     if basename(path).startswith('incompat-'):
         incompats.append(content)
     else:
         features.append(content)
 
 # Put the insertion markers back on the end, so they're ready for next time.
 feature_block = '\n\n'.join(features + [FEATURE_MARK])
 incompat_block = '\n\n'.join(incompats + [INCOMPAT_MARK])
 
 # 2. Update the target file ---------------------------------------------------
 
 with io.open(target, encoding='utf-8') as f:
     content = f.read()
 
 assert content.count(FEATURE_MARK) == 1
 assert content.count(INCOMPAT_MARK) == 1
 
 content = content.replace(FEATURE_MARK, feature_block)
 content = content.replace(INCOMPAT_MARK, incompat_block)
 
 # Clean trailing whitespace
 content = '\n'.join(l.rstrip() for l in content.splitlines())
 
 with io.open(target, 'w', encoding='utf-8') as f:
     f.write(content)
 
 # 3. Stage the changes in git -------------------------------------------------
 
 for file in files:
     check_call(['git', 'rm', file])
 
 check_call(['git', 'add', target])
 
 print("Merged what's new changes. Check the diff and commit the change.")