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copied!<p>This problem is easier/more efficient to solve using a loop, but if you really, really want to write a recursive solution, let's see how to do it. First example, how to count the number of lower case letters in a string (this is the correct implementation of your <code>string()</code> function):</p> <pre><code>import string def countString(strg): if not strg: # if it's the empty string return 0 # then it has 0 letters elif strg[0] in string.ascii_lowercase: # if the first char is a letter return 1 + countString(strg[1:]) # add 1 and continue with recursion else: # if the first char is not a letter raise Exception, 'Incorrect Letters' # then throw an exception countString('abcd') => 4 countString('ab$cd') => Exception: Incorrect Letters </code></pre> <p>The above will return the number of lower case letters in the input string, or throw an exception if a non-letter character was found. Notice that you can't just print a message if a non-letter character appears, it's necessary to stop the recursion, too - that's why I'm raising an exception.</p> <p>Second example, how to count the number of occurrences of a character in a string (this answers the question in the title), it's similar to the previous example, but it only counts the character passed as parameter:</p> <pre><code>def countChar(strg, ch): if not strg: # if it's the empty string return 0 # then ch's count is 0 elif strg[0] == ch: # if the first char is ch return 1 + countChar(strg[1:], ch) # add 1 and continue with recursion else: # if the first char is not ch return countChar(strg[1:], ch) # simply continue with recursion countChar('abcdeabca', 'a') => 3 countChar('abcdeabca', 'x') => 0 </code></pre>

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