added note about list concatenation and memory usage. unrelatedly, added nonbreaking spaces around long dashes.

your-first-python-program.html

@@ -66,7 +66,7 @@ if __name__ == '__main__':
 
 <p>What just happened? You executed your first Python program. You called the Python intepreter on the command line, and you passed the name of the script you wanted Python to execute. The script defines a single function, the <code>approximate_size()</code> function, which takes an exact file size in bytes and calculates a &#8220;pretty&#8221; (but approximate) size. (You&#8217;ve probably seen this in Windows Explorer, or the Mac OS X Finder, or Nautilus or Dolphin or Thunar on Linux. If you display a folder of documents as a multi-column list, it will display a table with the document icon, the document name, the size, type, last-modified date, and so on. If the folder contains a 1093-byte file named <code>TODO</code>, your file manager won&#8217;t display <code>TODO 1093 bytes</code>; it&#8217;ll say something like <code>TODO 1 KB</code> instead. That&#8217;s what the <code>approximate_size()</code> function does.)
 
-<p>Look at the bottom of the script, and you&#8217;ll see two calls to <code>print(approximate_size(<var>arguments</var>))</code>. These are function calls &mdash; first calling the <code>approximate_size()</code> function and passing a number of arguments, then taking the return value and passing it straight on to the <code>print()</code> function. The <code>print()</code> function is built-in; you&#8217;ll never see an explicit declaration of it. You can just use it, anytime, anywhere. (There are lots of built-in functions, and lots more functions that are separated into <i>modules</i>. Patience, grasshopper.)
+<p>Look at the bottom of the script, and you&#8217;ll see two calls to <code>print(approximate_size(<var>arguments</var>))</code>. These are function calls&nbsp;&mdash;&nbsp;first calling the <code>approximate_size()</code> function and passing a number of arguments, then taking the return value and passing it straight on to the <code>print()</code> function. The <code>print()</code> function is built-in; you&#8217;ll never see an explicit declaration of it. You can just use it, anytime, anywhere. (There are lots of built-in functions, and lots more functions that are separated into <i>modules</i>. Patience, grasshopper.)
 
 <p>So why does running the script on the command line give you the same output every time? We&#8217;ll get to that. First, let&#8217;s look at that <code>approximate_size()</code> function.
 
@@ -81,7 +81,7 @@ if __name__ == '__main__':
 <blockquote class=note>
 <p><span class=u>&#x261E;</span>In some languages, functions (that return a value) start with <code>function</code>, and subroutines (that do not return a value) start with <code>sub</code>. There are no subroutines in Python. Everything is a function, all functions return a value (even if it&#8217;s <code>None</code>), and all functions start with <code>def</code>.
 </blockquote>
-<p>The <code>approximate_size()</code> function takes the two arguments &mdash; <var>size</var> and <var>a_kilobyte_is_1024_bytes</var> &mdash; but neither argument specifies a datatype. In Python, variables are never explicitly typed. Python figures out what type a variable is and keeps track of it internally.
+<p>The <code>approximate_size()</code> function takes the two arguments&nbsp;&mdash;&nbsp;<var>size</var> and <var>a_kilobyte_is_1024_bytes</var>&nbsp;&mdash;&nbsp;but neither argument specifies a datatype. In Python, variables are never explicitly typed. Python figures out what type a variable is and keeps track of it internally.
 <blockquote class='note compare java'>
 <p><span class=u>&#x261E;</span>In Java and other statically-typed languages, you must specify the datatype of the function return value and each function argument. In Python, you never explicitly specify the datatype of anything. Based on what value you assign, Python keeps track of the datatype internally.
 </blockquote>