t and updates each element. <tt>len</tt>
returns the number of elements in the list. <tt>range</tt> returns
a list of indices from 0 to <i>n</i>-1, where <i>n</i> is the length of
the list. Each time through the loop <tt>i</tt> gets the index
of the next element. The assignment statement in the body uses
<tt>i</tt> to read the old value of the element and to assign the
new value.<br />
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A <tt>for</tt> loop over an empty list never exec