title: Why does exponential notation with decimal values fail?
body: <p>Conventionally <code>1e3</code> means <code>10**3</code>.</p>
  
  <pre><code>&gt;&gt;&gt; 1e3
  1000.0
  &gt;&gt;&gt; 10**3
  1000
  </code></pre>
  
  <p>Similar case is <code>exp(3)</code> compared to <code>e**3</code>.</p>
  
  <pre><code>&gt;&gt;&gt; exp(3)
  20.085536923187668
  &gt;&gt;&gt; e**3
  20.085536923187664
  </code></pre>
  
  <p>However now notice if the exponent is a <code>float</code> value:</p>
  
  <pre><code>&gt;&gt;&gt; exp(3.1)
  22.197951281441636
  &gt;&gt;&gt; e**3.1
  22.197951281441632
  </code></pre>
  
  <p>which is fine. Now for the first example:</p>
  
  <pre><code>&gt;&gt;&gt; 1e3.1
    File "&lt;stdin&gt;", line 1
      1e3.1
          ^
  SyntaxError: invalid syntax
  &gt;&gt;&gt; 10**3.1
  1258.9254117941675
  </code></pre>
  
  <p>which shows <code>Python</code> does not like <code>1e3.1</code>, <code>Fortran</code> too.
  Regardless it could be a standard (!) why it is like that?</p>