diff --git a/pdf/index_for_pdf.html b/pdf/index_for_pdf.html
index a0adbc0..6589c0a 100644
--- a/pdf/index_for_pdf.html
+++ b/pdf/index_for_pdf.html
@@ -12,15 +12,15 @@
 <strong>asyncio module, <a href="#coroutines">33</a></strong><br>
 <strong>audio, <a href="#audio">40</a>-<a href="#writefloatsamplestowavfile">41</a>, <a href="#sound">42</a></strong>  </p>
 <h3 id="b">B</h3>
-<p><strong>beautifulsoup library, <a href="#scraping">35</a></strong><br>
+<p><strong>beautifulsoup library, <a href="#scrapespythonsurlversionnumberandlogofromitswikipediapage">35</a></strong><br>
 <strong>binary representation, <a href="#ints">7</a>, <a href="#binhex">8</a></strong><br>
 <strong>bitwise operators, <a href="#bitwiseoperators">8</a></strong><br>
 <strong>bottle library, <a href="#web">36</a></strong><br>
-<strong>bytes, <a href="#bytes">28</a></strong>  </p>
+<strong>bytes, <a href="#open">22</a>-<a href="#modes">23</a>, <a href="#pickle">25</a>, <a href="#bytes">28</a>-<a href="#integertypesuseacapitalletterforunsignedtypeminimumandstandardsizesareinbrackets">29</a></strong>  </p>
 <h3 id="c">C</h3>
 <p><strong>cache, <a href="#lrucache">13</a></strong><br>
 <strong>callable, <a href="#callable">17</a></strong><br>
-<strong>class, <a href="#type">4</a>, <a href="#class">14</a>-<a href="#abcsequence">19</a>, <a href="#metaprograming">31</a>-<a href="#metaclass">32</a></strong><br>
+<strong>class, <a href="#type">4</a>, <a href="#class">14</a>-<a href="#inline-2">20</a>, <a href="#metaprograming">31</a>-<a href="#metaclass">32</a></strong><br>
 <strong>closure, <a href="#closure">12</a>-<a href="#decorator">13</a></strong><br>
 <strong>collection, <a href="#abstractbaseclasses">4</a>, <a href="#collection">18</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a></strong><br>
 <strong>collections module, <a href="#dictionary">2</a>, <a href="#namedtuple">3</a>, <a href="#abstractbaseclasses">4</a>, <a href="#abcsequence">19</a>, <a href="#deque">29</a></strong><br>
@@ -55,14 +55,14 @@
 <strong>functools module, <a href="#mapfilterreduce">11</a>, <a href="#partial">12</a>, <a href="#debuggerexample">13</a>, <a href="#sortable">16</a></strong><br>
 <strong>futures, <a href="#threadpoolexecutor">30</a></strong>  </p>
 <h3 id="g">G</h3>
-<p><strong>generators, <a href="#generator">4</a>, <a href="#comprehensions">11</a></strong><br>
+<p><strong>generators, <a href="#generator">4</a>, <a href="#comprehensions">11</a>, <a href="#iterator-1">17</a></strong><br>
 <strong>global keyword, <a href="#nonlocal">12</a></strong><br>
 <strong>gui, <a href="#pysimplegui">48</a></strong>  </p>
 <h3 id="h">H</h3>
 <p><strong>hashable, <a href="#dataclass">15</a>, <a href="#hashable">16</a></strong><br>
 <strong>hexadecimal representation, <a href="#ints">7</a>, <a href="#binhex">8</a>, <a href="#encode-1">28</a></strong>  </p>
 <h3 id="i">I</h3>
-<p><strong>image, <a href="#scraping">35</a>, <a href="#image">39</a>-<a href="#animation">40</a>, <a href="#surface">42</a>-<a href="#basicmariobrothersexample">43</a></strong><br>
+<p><strong>image, <a href="#scrapespythonsurlversionnumberandlogofromitswikipediapage">35</a>, <a href="#image">39</a>-<a href="#animation">40</a>, <a href="#surface">42</a>-<a href="#basicmariobrothersexample">43</a></strong><br>
 <strong>inline, <a href="#otheruses">11</a>-<a href="#namedtupleenumdataclass">12</a>, <a href="#inline-1">15</a>, <a href="#inline-2">20</a></strong><br>
 <strong>input function, <a href="#input">22</a></strong><br>
 <strong>introspection, <a href="#introspection">31</a></strong><br>
@@ -77,10 +77,10 @@
 <p><strong>lambda, <a href="#lambda">11</a></strong><br>
 <strong>list comprehension, <a href="#comprehensions">11</a></strong><br>
 <strong>lists, <a href="#list">1</a>-<a href="#list">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">11</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
-<strong>locks, <a href="#lock">29</a>, <a href="#coroutines">33</a></strong><br>
+<strong>locks, <a href="#lock">30</a>, <a href="#coroutines">33</a></strong><br>
 <strong>logging, <a href="#logging">35</a></strong>  </p>
 <h3 id="m">M</h3>
-<p><strong>main function, <a href="#main">1</a>, <a href="#basicscripttemplate">41</a></strong><br>
+<p><strong>main function, <a href="#main">1</a>, <a href="#basicscripttemplate">49</a></strong><br>
 <strong>map function, <a href="#mapfilterreduce">11</a>, <a href="#operator">31</a></strong><br>
 <strong>math module, <a href="#math">7</a></strong><br>
 <strong>memoryviews, <a href="#memoryview">29</a></strong><br>
@@ -101,7 +101,7 @@
 <strong>path, <a href="#path">23</a>-<a href="#direntry">24</a></strong><br>
 <strong>pickle module, <a href="#pickle">25</a></strong><br>
 <strong>pillow library, <a href="#image">39</a></strong><br>
-<strong>plotting, <a href="#plot">34</a>, <a href="#plotly">47</a></strong><br>
+<strong>plotting, <a href="#plot">34</a>, <a href="#plotly">47</a>-<a href="#confirmedcovidcasesdowjonesgoldandbitcoinprice">48</a></strong><br>
 <strong>print function, <a href="#print">22</a></strong><br>
 <strong>profiling, <a href="#profiling">36</a>-<a href="#timingasnippet">37</a></strong><br>
 <strong>progress bar, <a href="#progressbar">34</a></strong><br>
@@ -115,7 +115,7 @@
 <strong>recursion, <a href="#lrucache">13</a></strong><br>
 <strong>reduce function, <a href="#mapfilterreduce">11</a>, <a href="#operator">31</a></strong><br>
 <strong>regular expressions, <a href="#regex">5</a>-<a href="#specialsequences">6</a></strong><br>
-<strong>requests library, <a href="#scraping">35</a>, <a href="#test">36</a></strong>  </p>
+<strong>requests library, <a href="#scrapespythonsurlversionnumberandlogofromitswikipediapage">35</a>, <a href="#test">36</a></strong>  </p>
 <h3 id="s">S</h3>
 <p><strong>scraping, <a href="#scraping">35</a>, <a href="#basicmariobrothersexample">43</a>, <a href="#encodedecode">46</a>, <a href="#coviddeathsbycontinent">47</a>-<a href="#confirmedcovidcasesdowjonesgoldandbitcoinprice">48</a></strong><br>
 <strong>sequence, <a href="#abstractbaseclasses">4</a>, <a href="#sequence">18</a>-<a href="#abcsequence">19</a></strong><br>
@@ -132,7 +132,7 @@
 <strong>subprocess module, <a href="#sends11tothebasiccalculatorandcapturesitsoutput">25</a></strong><br>
 <strong>super function, <a href="#inheritance">14</a></strong><br>
 <strong>synthesizer, <a href="#synthesizer">41</a></strong><br>
-<strong>sys module, <a href="#lrucache">15</a>, <a href="#exit">21</a>-<a href="#print">22</a></strong> </p>
+<strong>sys module, <a href="#lrucache">13</a>, <a href="#exit">21</a>-<a href="#print">22</a></strong> </p>
 <h3 id="t">T</h3>
 <p><strong>table, <a href="#example">27</a>, <a href="#table">34</a>, <a href="#dataframe">45</a>-<a href="#encodedecode">46</a></strong><br>
 <strong>template, <a href="#format">6</a>, <a href="#dynamicrequest">36</a></strong><br>
diff --git a/pdf/index_for_pdf_print.html b/pdf/index_for_pdf_print.html
index 61fa07c..806bc81 100644
--- a/pdf/index_for_pdf_print.html
+++ b/pdf/index_for_pdf_print.html
@@ -16,11 +16,11 @@
 <strong>binary representation, 7, 8</strong><br>
 <strong>bitwise operators, 8</strong><br>
 <strong>bottle library, 36</strong><br>
-<strong>bytes, 28</strong>  </p>
+<strong>bytes, 22-23, 25, 28-29</strong>  </p>
 <h3 id="c">C</h3>
 <p><strong>cache, 13</strong><br>
 <strong>callable, 17</strong><br>
-<strong>class, 4, 14-19, 31-32</strong><br>
+<strong>class, 4, 14-20, 31-32</strong><br>
 <strong>closure, 12-13</strong><br>
 <strong>collection, 4, 18, 19</strong><br>
 <strong>collections module, 2, 3, 4, 19, 29</strong><br>
@@ -55,7 +55,7 @@
 <strong>functools module, 11, 12, 13, 16</strong><br>
 <strong>futures, 30</strong>  </p>
 <h3 id="g">G</h3>
-<p><strong>generators, 4, 11</strong><br>
+<p><strong>generators, 4, 11, 17</strong><br>
 <strong>global keyword, 12</strong><br>
 <strong>gui, 48</strong>  </p>
 <h3 id="h">H</h3>
@@ -77,10 +77,10 @@
 <p><strong>lambda, 11</strong><br>
 <strong>list comprehension, 11</strong><br>
 <strong>lists, 1-2, 4, 11, 19, 21</strong><br>
-<strong>locks, 29, 33</strong><br>
+<strong>locks, 30, 33</strong><br>
 <strong>logging, 35</strong>  </p>
 <h3 id="m">M</h3>
-<p><strong>main function, 1, 41</strong><br>
+<p><strong>main function, 1, 49</strong><br>
 <strong>map function, 11, 31</strong><br>
 <strong>math module, 7</strong><br>
 <strong>memoryviews, 29</strong><br>
@@ -132,7 +132,7 @@
 <strong>subprocess module, 25</strong><br>
 <strong>super function, 14</strong><br>
 <strong>synthesizer, 41</strong><br>
-<strong>sys module, 15, 21-22</strong> </p>
+<strong>sys module, 13, 21-22</strong> </p>
 <h3 id="t">T</h3>
 <p><strong>table, 27, 34, 45-46</strong><br>
 <strong>template, 6, 36</strong><br>