&gt;&gt;&gt; s = [.1,.1,.1,.1,.1,.1,.1,.1,.1,.1]<br>&gt;&gt;&gt; sum(s)<br>0.9999999999999999<br><span style="font-family: courier new,monospace;">&gt;&gt;&gt; print(sum(s))</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">1.0</span>      Why?<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">&gt;&gt;&gt; f = 0.9999999999999999</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">&gt;&gt;&gt; f**100</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">0.9999999999999889</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">&gt;&gt;&gt; print(f**100)</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">1.0</span>      Why?<br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">&gt;&gt;&gt; f**10000</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">0.9999999999988898</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">&gt;&gt;&gt; print(f**10000)</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">0.999999999999</span>   <span style="font-family: courier new,monospace;"></span><span style="font-family: courier new,monospace;"></span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">&gt;&gt;&gt; from math import fsum</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">&gt;&gt;&gt; fsum(s)</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">1.0</span><br>&gt;&gt;&gt; from math import fsum<br>&gt;&gt;&gt; fsum(s)   <br>1.0        See &lt;<a href="http://docs.python.org/py3k/library/math.html?highlight=fsum#math.fsum">http://docs.python.org/py3k/library/math.html?highlight=fsum#math.fsum</a>&gt;<br>

<br>The &quot;Why?&quot;s mark what are puzzles for me.<br><br>I see nothing in the doc for print() that explains these: &lt;<a href="http://docs.python.org/py3k/library/functions.html?highlight=print#print">http://docs.python.org/py3k/library/functions.html?highlight=print#print</a>&gt;, but I&#39;m sure a Tutor can.<br>

<br>Dick Moores<br>