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<div class="section" id="python-2-versus-python-3">
<span id="py2-vs-py3"></span><h1>Python 2 versus Python 3<a class="headerlink" href="#python-2-versus-python-3" title="Permalink to this headline"></a></h1>
<p>now that Python version 2 has officially reached end of life, most recent information is in/about Python 3.</p>
<p>But you will still find a lot of older example code online in Python2, rather than Python3</p>
<p>For the most part, they are the same – so you can use those examples to learn from.</p>
<p>There are a lot of subtle differences that you don’t need to concern yourself with just yet.</p>
<p>But a couple that you’ll need to know right off the bat:</p>
<div class="section" id="print">
<h2>print()<a class="headerlink" href="#print" title="Permalink to this headline"></a></h2>
<p>In Python2, <code class="docutils literal notranslate"><span class="pre">print</span></code> is a “statement”, rather than a function. That means it didn’t require parentheses around what you want printed:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="nb">print</span> <span class="n">something</span><span class="p">,</span> <span class="n">something_else</span>
</pre></div>
</div>
<p>This made it a bit less flexible and powerful.</p>
<p>But – if you try to use it that way in Python3, you’ll get an error:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">15</span><span class="p">]:</span> <span class="nb">print</span> <span class="s2">"this"</span>
<span class="n">File</span> <span class="s2">"<ipython-input-15-70c8add5d16e>"</span><span class="p">,</span> <span class="n">line</span> <span class="mi">1</span>
<span class="nb">print</span> <span class="s2">"this"</span>
<span class="o">^</span>
<span class="ne">SyntaxError</span><span class="p">:</span> <span class="n">Missing</span> <span class="n">parentheses</span> <span class="ow">in</span> <span class="n">call</span> <span class="n">to</span> <span class="s1">'print'</span>
</pre></div>
</div>
<p>So – if you get this error, simply add the parentheses:</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="gp">In [16]: </span><span class="nb">print</span><span class="p">(</span><span class="s2">"this"</span><span class="p">)</span>
<span class="go">this</span>
</pre></div>
</div>
</div>
<div class="section" id="division">
<h2>Division<a class="headerlink" href="#division" title="Permalink to this headline"></a></h2>
<p>In python 3, the division operator is “smart” when you divide integers:</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="gp">In [17]: </span><span class="mi">1</span> <span class="o">/</span> <span class="mi">2</span>
<span class="gh">Out[17]: </span><span class="go">0.5</span>
</pre></div>
</div>
<p>However in Python2, integer division, will give you an integer result:</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="gp">In [1]: </span><span class="mi">1</span><span class="o">/</span><span class="mi">2</span>
<span class="gh">Out[1]: </span><span class="go">0</span>
</pre></div>
</div>
<p>In both versions, you can get “integer division” if you want it with a double slash:</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="gp">In [1]: </span><span class="mi">1</span><span class="o">//</span><span class="mi">2</span>
<span class="gh">Out[1]: </span><span class="go">0</span>
</pre></div>
</div>
<p>And in Python2, you can get the behavior of Python3 with “true division”:</p>
<div class="highlight-ipython notranslate"><div class="highlight"><pre><span></span><span class="gp">In [2]: </span><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">division</span>
<span class="gp">In [3]: </span><span class="mi">1</span><span class="o">/</span><span class="mi">2</span>
<span class="gh">Out[3]: </span><span class="go">0.5</span>
</pre></div>
</div>
<p>For the most part, you just need to be a bit careful with the rare cases where Python2 code counts on integer division.</p>
</div>
<div class="section" id="iterators-vs-lists">
<h2>Iterators vs Lists<a class="headerlink" href="#iterators-vs-lists" title="Permalink to this headline"></a></h2>
<p>In Python2, a number of functions returned a full list of the contents. But most of the time, you didn’t need a list – you only needed a way to loop through all the items returned. Such an object is called an “iterable” – more about that later in the class. But for now, if you get an error like:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="ne">TypeError</span><span class="p">:</span> <span class="s1">'dict_keys'</span> <span class="nb">object</span> <span class="n">does</span> <span class="ow">not</span> <span class="n">support</span> <span class="n">indexing</span>
</pre></div>
</div>
<p>Then you likely got an iterator, rather than a “proper” list. You can fix this by making a list out of it:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">list</span><span class="p">(</span><span class="n">an_iterator</span><span class="p">)</span>
</pre></div>
</div>
<p>the list constructor will make a list out of any iterable. So you can now index it, etc.</p>
</div>
<div class="section" id="other-python2-python3-differences">
<h2>Other Python2 / Python3 differences<a class="headerlink" href="#other-python2-python3-differences" title="Permalink to this headline"></a></h2>
<p>The most drastic difference (improvement!) is better Unicode support, and better bytes / Unicode separation.</p>
<p>Most of the other differences are essentially implementation details, like getting iterators instead of sequences – we’ll talk about that more when it comes up in a later lesson.</p>
<p>There are also a few syntax differences with more advanced topics: Exceptions, <code class="docutils literal notranslate"><span class="pre">super()</span></code>, etc.</p>
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