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<p>This statement assigns the name <code>x</code> to the value <code>3</code>. Like a suitcase tag, the name <code>x</code> is bound to the value <code>3</code>.</p>
<p>Python first evaluates the expression on the right-hand side of the <code>=</code> assignment operator, then binds the name <code>x</code> to the resulting value.</p>
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<p>The below statement re-assigns the name <code>x</code>. Think of this as moving the suitcase tag to a different suitcase.</p>
<p>Good style practices can involve comments, meaningful names, whitespace, markdown cells interspersed with code cells, etc. <ahref="https://inferentialthinking.com/chapters/03/2/Names.html">Ch 3.2</a> of <em>Inferential Thinking</em> describes meaningful names; we discuss comments below.</p>
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<p><strong>Comments</strong> are used to explain what code does. Good programmers write code that is self-evident and use comments only where necessary.</p>
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<p>In Python, you can write comments in the same line as code (“in-line” comments) using <code>#</code>:</p>
<p>Once you fix syntax errors, you may still encounter <strong>functionality errors</strong>, which can be errors caused during execution that leads to your program crashing. Here’s one common one:</p>
<p><strong>Concatenation operation</strong>: The <code>+</code> operator works differently on string data types. Instead of adding numerically, it “adds textually,” which is more formally called <strong>concatenation</strong>:</p>
<p><strong>Length function</strong>: There is one function not shown above that would be useful to you know, and that is <code>len(s)</code>, which takes a string argument and returns its length.</p>
<h2class="anchored" data-anchor-id="boolean-data-type">Boolean Data Type</h2>
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<p>The Boolean data type (<code>bool</code>) has exactly two values: <code>True</code> and <code>False</code>. Note that boolean values are <em>not</em> strings!</p>
<p>We can also <strong>typecast</strong>, or convert values between data types. These typecasting functions take in one typed argument and return another typed argument, then return that value as a different type. The function name is generally the type. Note that data type conversion is only valid “when it makes sense.” We’ll talk about this more later.</p>
<divclass="sourceCode cell-code" id="cb11"><preclass="sourceCode python code-with-copy"><codeclass="sourceCode python"><spanid="cb11-1"><ahref="#cb11-1" aria-hidden="true" tabindex="-1"></a>x <spanclass="op">=</span><spanclass="dv">3</span><spanclass="co"># what type is x?</span></span>
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<spanid="cb11-2"><ahref="#cb11-2" aria-hidden="true" tabindex="-1"></a><spanclass="bu">str</span>(x) <spanclass="co"># returns a value of type string</span></span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
<divclass="sourceCode cell-code" id="cb13"><preclass="sourceCode python code-with-copy"><codeclass="sourceCode python"><spanid="cb13-1"><ahref="#cb13-1" aria-hidden="true" tabindex="-1"></a>s <spanclass="op">=</span><spanclass="st">"5"</span><spanclass="co"># what type is x?</span></span>
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<spanid="cb13-2"><ahref="#cb13-2" aria-hidden="true" tabindex="-1"></a><spanclass="bu">float</span>(s) <spanclass="co"># what type is returned?</span></span></code><buttontitle="Copy to Clipboard" class="code-copy-button"><iclass="bi"></i></button></pre></div>
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