title: Cannot print out the PE structure by LIEF (python)
body: <p>This is my code.</p>
  <p>In This part, I import the LIEF lib and add the file that I want to print out the header</p>
  <pre><code>import lief
  exe_path = '/Boom'
  exe_object: lief.PE = lief.parse(exe_path)
  </code></pre>
  <p>About this part, I tried to print the header.</p>
  <pre><code>print('Header')
  print(exe_object.header)
  </code></pre>
  <p>The result is</p>
  <pre><code>AttributeError    Traceback (most recent call last)
  Input In [30], in &lt;cell line: 2&gt;()
        1 print('DOS Header')
  ----&gt; 2 print(exe_object.dos_header)
        4 print('PE Header')
        5 print(exe_object.header)
      AttributeError: 'NoneType' object has no attribute 'dos_header'
  </code></pre>
  <p>The expect result:</p>
  <p>Header</p>
  <p>Signature:                    50 45 0 0</p>
  <p>Machine:                      I386</p>
  <p>Number Of Sections:           5</p>
  <p>Pointer To Symbol Table:      0</p>
  <p>Number Of Symbols:            0</p>
  <p>Size Of Optional Header:      e0</p>
  <p>Characteristics:              EXECUTABLE_IMAGE - CHARA_32BIT_MACHINE</p>
  <p>Time Date Stamp:              56ac266b</p>