Changed the implementation of exercise 3 in python essentials to make it

faster, more pythonic and use techniques explained in the text

Author: Jez

source/rst/python_essentials.rst

@@ -1049,13 +1049,10 @@ Here's one solution:
 
 .. code-block:: python3
 
-    def f(string):
-        count = 0
-        for letter in string:
-            if letter == letter.upper() and letter.isalpha():
-                count += 1
-        return count
-    f('The Rain in Spain')
+    def count_uppercase_chars(s):
+        return sum([c.isupper() for c in s]
+
+    count_uppercase_chars('The Rain in Spain')
 
 
 Exercise 4