[firefox] Fix script (#284)

- batch HTTP URL fetching by 20 to reduce the number of unnecessary retries,
- search for c-release-date directly.

src/firefox.py

@@ -1,5 +1,6 @@
 import re
 import urllib.parse
+from itertools import islice
 
 from bs4 import BeautifulSoup
 from common import dates, http, releasedata
@@ -8,24 +9,39 @@ from common import dates, http, releasedata
 
 Versions lower than 10.0 are ignored because too difficult to parse."""
 
+
+# Will be replaced by itertools.batched in Python 3.12+.
+# See https://docs.python.org/3/library/itertools.html#itertools.batched.
+def batched(iterable: iter, n: int) -> iter:
+    if n < 1:
+        msg = 'n must be at least one'
+        raise ValueError(msg)
+    it = iter(iterable)
+    while batch := tuple(islice(it, n)):
+        yield batch
+
+
 product = releasedata.Product("firefox")
 releases_page = http.fetch_url("https://www.mozilla.org/en-US/firefox/releases/")
 releases_soup = BeautifulSoup(releases_page.text, features="html5lib")
 releases_list = releases_soup.find_all("ol", class_="c-release-list")
 release_notes_urls = [urllib.parse.urljoin(releases_page.url, p.get("href")) for p in releases_list[0].find_all("a")]
 
-for release_notes in http.fetch_urls(release_notes_urls):
-    version = release_notes.url.split("/")[-3]
+for batch_release_notes_urls in batched(release_notes_urls, 20):
+    for release_notes in http.fetch_urls(batch_release_notes_urls):
+        version = release_notes.url.split("/")[-3]
 
-    release_notes_soup = BeautifulSoup(release_notes.text, features="html5lib")
-    if release_notes_soup.find("div", class_="c-release-version"):
-        date = dates.parse_date(release_notes_soup.find("p", class_="c-release-date").get_text())
-        product.declare_version(version, date)
+        release_notes_soup = BeautifulSoup(release_notes.text, features="html5lib")
+        date_elt = release_notes_soup.find(class_="c-release-date")
+        if date_elt:
+            date = dates.parse_date(date_elt.get_text())
+            product.declare_version(version, date)
+            continue
 
-    elif release_notes_soup.find("small", string=re.compile("^.?First offered")):
-        element = release_notes_soup.find("small", string=re.compile("^.?First offered"))
-        date = dates.parse_date(' '.join(element.get_text().split(" ")[-3:]))  # get last 3 words
-        product.declare_version(version, date)
-    # versions < 10.0 are ignored
+        date_elt = release_notes_soup.find("small", string=re.compile("^.?First offered"))
+        if date_elt:
+            date = dates.parse_date(' '.join(date_elt.get_text().split(" ")[-3:]))  # get last 3 words
+            product.declare_version(version, date)
+        # versions < 10.0 are ignored
 
 product.write()