Apply various minor refactorings

Improve readability and fix a few Python warnings (line too long, exception too broad...) through various minor refactorings.

src/cos.py

@@ -3,6 +3,7 @@ from bs4 import BeautifulSoup
 from common import endoflife
 from datetime import datetime
 
+DATE_FORMAT = '%b %d, %Y'
 REGEX = r"^(cos-\d+-\d+-\d+-\d+)"
 
 
@@ -16,34 +17,35 @@ def fetch_all_milestones():
 
 
 def fetch_milestone(channel):
-    url = "https://cloud.google.com/container-optimized-os/docs/release-notes/m{}".format(channel)
+    url = f"https://cloud.google.com/container-optimized-os/docs/release-notes/m{channel}"
     # Retry as Google Docs often returns SSL errors.
     response = endoflife.fetch_url(url, retry_count=10)
     return BeautifulSoup(response, features="html5lib")
 
 
+def parse_date(d):
+    # If the date begins with a >3 letter month name, trim it to just 3 letters
+    # Strip out the Date: section from the start
+    d = re.sub(r'(?:Date\: )?(\w{3})(?:\w{1,4})? (\d{1,2}), (\d{4})', r'\1 \2, \3', d)
+    return datetime.strptime(d, DATE_FORMAT).strftime('%Y-%m-%d')
+
+
 def parse_soup_for_versions(soup):
     """Takes soup, and returns a dictionary of versions and their release dates
     """
     versions = {}
     for article in soup.find_all('article', class_='devsite-article'):
-        def parse_date(d):
-            # If the date begins with a >3 letter month name, trim it to just 3 letters
-            # Strip out the Date: section from the start
-            d = re.sub(r'(?:Date\: )?(\w{3})(?:\w{1,4})? (\d{1,2}), (\d{4})', r'\1 \2, \3', d)
-            return datetime.strptime(d, date_format).strftime('%Y-%m-%d')
         # h2 contains the date, which we parse
         for heading in article.find_all(['h2', 'h3']):
             version = heading.get('data-text')
             m = re.match(REGEX, version)
             if m:
                 version = m.group(1)
-                date_format = '%b %d, %Y'
                 try:
-                    # The first row is the header, so we pick the first td in the second row
+                    # 1st row is the header, so pick the first td in the 2nd row
                     d = heading.find_next('tr').find_next('tr').find_next('td').text
-                except:
-                    # In some older releases, it is mentioned as Date: [Date] in the text
+                except AttributeError:
+                    # In some older releases, it is mentioned as Date: [Date]
                     d = heading.find_next('i').text
                 try:
                     date = parse_date(d)
@@ -51,7 +53,7 @@ def parse_soup_for_versions(soup):
                     d = heading.find_previous('h2').get('data-text')
                     date = parse_date(d)
                 versions[version] = date
-                print("%s: %s" % (version, date))
+                print(f"{version}: {date}")
 
     return versions