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[Tut] Python One Line FizzBuzz

#1
Python One Line FizzBuzz

<div><p>The <a href="https://en.wikipedia.org/wiki/Fizz_buzz" target="_blank" rel="noreferrer noopener">FizzBuzz </a>problem is a common exercise posed in code interviews to test your proficiency in writing simple Python code.</p>
<p><strong>Problem</strong>: Print all numbers from 1-100 to the shell with three exceptions: </p>
<ul>
<li>For each number divisible by three you print <code>"Fizz"</code>, </li>
<li>For each number divisible by five you print <code>"Buzz"</code>, and</li>
<li>For each number divisible by three and five you print <code>"FizzBuzz"</code>. </li>
</ul>
<p><strong>Example</strong>: The first 15 numbers of the FizzBuzz sequence are the following.</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
...</pre>
<p>How to write a <a href="https://blog.finxter.com/python-one-line-x/" target="_blank" rel="noreferrer noopener" title="Python One Line X">Python one-liner</a> that solves this problem?</p>
<p>Here’s an interactive overview:</p>
<p> <iframe src="https://repl.it/@finxter/RashMintyConstants?lite=true" scrolling="no" allowtransparency="true" allowfullscreen="true" sandbox="allow-forms allow-pointer-lock allow-popups allow-same-origin allow-scripts allow-modals" width="100%" height="600px" frameborder="no"></iframe> </p>
<p><em><strong>Exercise</strong>: Do both one-liners produce the same results? Run the code to check!</em></p>
<p>Let’s dive into those one-liners to gain a deeper understanding and improve your Python skills!</p>
<h2>FizzBuzz One-Liner 1: Generator Expression + String Concatenation + Short Circuiting</h2>
<p>The following one-liner solves the problem in an elegant way using a fine understanding of more advanced Python features (<a href="http://michaeljgilliland.blogspot.com/2013/01/one-line-fizz-buzz-test-in-python.html" target="_blank" rel="noreferrer noopener" title="http://michaeljgilliland.blogspot.com/2013/01/one-line-fizz-buzz-test-in-python.html">source</a>). </p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">print('\n'.join('Fizz' * (i%3==0) + 'Buzz' * (i%5==0) or str(i) for i in range(1,101)))</pre>
<p>The one-liner creates a string using the <code><a href="https://blog.finxter.com/python-join-list/" title="Python Join List [Ultimate Guide]" target="_blank" rel="noreferrer noopener">join</a></code> function with the newline character as a delimiter. Here’s a short explanation of the function:</p>
<p class="has-pale-cyan-blue-background-color has-background">The <code>string.join(iterable)</code> method concatenates all the string elements in the <code>iterable</code> (such as a list, string, or tuple) and returns the result as a new string. The <code>string</code> on which you call it is the delimiter string—and it separates the individual elements. For example, <code>'-'.join(['hello', 'world'])</code> returns the joined string <code>'hello-world'</code>.</p>
<p>So, what’s the iterable, you pass into the <code>join()</code> function? It’s a generator expression of the form: <code>expression for variable in context</code>. You go over all integer values in the context 1 to 100 using the <code><a href="https://blog.finxter.com/python-join-list-range-a-helpful-guide/" title="Python Join List Range: A Helpful Guide" target="_blank" rel="noreferrer noopener">range()</a></code> function. So, you obtain the remaining <code>expression for i in range(1, 101)</code>. What’s the expression part?</p>
<p>It consists of three elements: </p>
<ul>
<li><code>'Fizz' * (i%3==0)</code> — The <a href="https://en.wikipedia.org/wiki/Modulo_operation" target="_blank" rel="noreferrer noopener" title="https://en.wikipedia.org/wiki/Modulo_operation">modulo </a>expression <code>i%3==0</code> returns <code>True</code> only if the integer <code>i</code> is divisible by 3, otherwise it returns <code>False</code>. So, you multiply the string <code>'Fizz'</code> either with <code>True</code> (=1) or with <code>False</code> (=0). As a result, you obtain the empty string <code>''</code> in all cases except if the integer <code>i</code> is divisible by 3—in which case you obtain the string <code>'Fizz'</code>. </li>
<li><code>'Buzz' * (i%5==0)</code>— The <a href="https://en.wikipedia.org/wiki/Modulo_operation" target="_blank" rel="noreferrer noopener">modulo </a>expression <code>i%5==0</code> returns <code>True</code> only if the integer <code>i</code> is divisible by 5, otherwise it returns <code>False</code>. So, you multiply the string <code>'Buzz'</code> either with <code>True</code> (=1) or with <code>False</code> (=0). As a result, you obtain the empty string <code>''</code> in all cases except if the integer <code>i</code> is divisible by 5—in which case you obtain the string <code>'Buzz'</code>.</li>
<li>You use string concatenation to glue together the previously obtained strings. In most cases, this will be the empty string. If <code>i</code> is divisible by 3, you obtain the string <code>'Fizz'</code>. If <code>i</code> is divisible by 5, you obtain the string <code>'Buzz'</code>. And if <code>i</code> is divisible by 3 and 5, you obtain the string <code>'FizzBuzz'</code>. </li>
<li><code>or str(i)</code> — In the case you obtained a non-empty string in <code>{'Fizz', 'Buzz', 'FizzBuzz'}</code> in the previous step, the <code><a href="https://blog.finxter.com/python-one-line-and-or/" title="Python One Line And/Or" target="_blank" rel="noreferrer noopener">or</a></code> operation simply returns this string. This is called <a href="https://blog.finxter.com/what-is-short-circuit-evaluation-in-python/" title="What is Short Circuit Evaluation in Python?" target="_blank" rel="noreferrer noopener">short circuiting</a>—and it’s used in many programming languages such as Python to improve efficiency of logical operations. </li>
<li>But if the string is empty, it is interpreted as a logical <code>False</code>. Thus, Python returns the second operand of the <code>or</code> operation. The second operand simply is the string representation of the integer <code>i</code>. </li>
</ul>
<p>A very interesting implementation of the FizzBuzz problem indeed!</p>
<h2>FizzBuzz One-Liner 2: Slicing</h2>
<p>An alternative is given in the following nice one-liner (source):</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">for i in range(1, 101): print('FizzBuzz'[i*i%3*4:8--i**4%5] or i)</pre>
<p>Wow—what a short and concise one-liner solution! But how does it work?</p>
<ul>
<li>You iterate over all values from <code>i=1</code> to <code>i=100</code> and print a string. So far so good. </li>
<li>You use the <code>or</code> operation and slicing to determine the string <code>'FizzBuzz'[start:end] or i</code> generates the output. </li>
<li>You use the property of short circuiting in Python: If <code>'FizzBuzz'[start:end]</code> is empty, the integer <code>i</code> is returned, otherwise, the non-empty string is returned.</li>
<li>You carve out a substring from <code>'FizzBuzz'</code> using <a href="https://blog.finxter.com/introduction-to-slicing-in-python/" target="_blank" rel="noreferrer noopener" title="Introduction to Slicing in Python">slicing </a>as follows.</li>
</ul>
<p>Slicing is a concept to carve out a substring from a given string. Use slicing notation <code>s[startConfusedtopConfusedtep]</code> to access every <code>step</code>-th element starting from index <code>start</code> (included) and ending in index <code>stop</code> (excluded). All three arguments are optional, so you can skip them to use the default values (<code>start=0</code>, <code>stop=len(lst)</code>, <code>step=1</code>). For example, the expression <code>s[2:4]</code> from string <code>'hello'</code> carves out the slice <code>'ll'</code> and the expression <code>s[:3:2]</code> carves out the slice <code>'hl'</code>.</p>
<p>In the example, you have the slicing operation <code>'FizzBuzz'[i*i%3*4:8--i**4%5]</code>. </p>
<ul>
<li><code>start = i*i%3*4</code> — Note that the multiplication <code>*</code> and modulo operation <code>%</code> have the same priority, so they are evaluated from left to right. If integer <code>i</code> is divisible by 3, <code>i*i</code> is also divisible by 3, and the start index is 0. In all other cases, the start index is 4. Thus, the slice either starts with <code>'Fizz'</code> or <code>'Buzz'</code>. </li>
<li><code>stop = 8--i**4%5</code> — This is 4 in all cases except if the number <code>i</code> is divisible by 5, in which case this is 8. </li>
</ul>
<p>So, there are four cases:</p>
<ul>
<li>The number is divisible only by 3: <code>start=0</code>, <code>stop=4</code> –&gt; <code>'Fizz'</code></li>
<li>The number is divisible only by 5: <code>start=4</code>, <code>stop=8</code> –&gt; <code>'Buzz'</code></li>
<li>The number is divisible by both 3 and 5: <code>start=0</code>, <code>stop=8</code> –&gt; <code>'FizzBuzz'</code></li>
<li>The number is divisible by neither 3 nor 5: <code>start = 4</code>, <code>stop=4</code> –&gt; <code>''</code></li>
</ul>
<p>Phew! This was a hard nut to crack, wasn’t it?</p>
<h2>Python One-Liner 3: Map + Lambda</h2>
<p>You can find detailed tutorials on the map and lambda functions here:</p>
<ul>
<li><a href="https://blog.finxter.com/daily-python-puzzle-string-encrpytion-ord-function-map-function/" title="Mastering the Python Map Function [+Video]" target="_blank" rel="noreferrer noopener"><a href="https://blog.finxter.com/daily-python-puzzle-string-encrpytion-ord-function-map-function/" target="_blank" rel="noreferrer noopener">Mastering the Python Map Function</a></a></li>
<li><a href="https://blog.finxter.com/a-simple-introduction-of-the-lambda-function-in-python/" title="Lambda Functions in Python: A Simple Introduction" target="_blank" rel="noreferrer noopener"><a href="https://blog.finxter.com/a-simple-introduction-of-the-lambda-function-in-python/" target="_blank" rel="noreferrer noopener">Lambda Functions in Python</a></a></li>
</ul>
<p>Those two functions can be used to solve the FizzBuzz problem (<a href="https://gist.github.com/konstantinfarrell/c4f84ea579615da63de0eb325753b71d" target="_blank" rel="noreferrer noopener" title="https://gist.github.com/konstantinfarrell/c4f84ea579615da63de0eb325753b71d">source</a>):</p>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">print(list(map(lambda i: "Fizz"*(i%3==0)+"Buzz"*(i%5==0) or str(i), range(1,101))))</pre>
<p>It’s similar to Method 1 and by now you’re able to figure it out. Think of the different values the integer <code>i</code> can take. </p>
<h2>Python One-Liners Book</h2>
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