fix escaping in jupyter notebook

also added some more comments above the change in word match regex of
last 2 commits

Author: bbelderbos

days/28-30-regex/regex.ipynb

@@ -247,7 +247,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Of course you can do the same with `words.split()` but if you have more requirements you might fit it in the same regex, for example let's only count words that start with a capital letter. I am using the _`[]` character class_ as an alternative to \\w here: "
+    "Of course you can do the same with `words.split()` but if you have more requirements you might fit it in the same regex, for example let's only count words that start with a capital letter.\n",
+    "\n",
+    "I am using two _character classes_ here (= pattern inside `[]`), the first to match a capital letter, the second to match 0 or more common word characters. \n",
+    "\n",
+    "Note I am escaping the single quote (') inside the second character class, because the regex pattern is wrapped inside single quotes as well: "
    ]
   },
   {
@@ -258,7 +262,7 @@
    "source": [
     "from collections import Counter\n",
     "\n",
-    "cnt = Counter(re.findall(r"[A-Z][A-Za-z0-9']*", text))\n",
+    "cnt = Counter(re.findall(r'[A-Z][A-Za-z0-9\\']*', text))\n",
     "cnt.most_common(5)"
    ]
   },
@@ -471,7 +475,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.1"
+   "version": "3.6.5"
   }
  },
  "nbformat": 4,