Drop rows with a 'question mark' value in any column in a pandas dataframe
<p>I want to remove all rows (or take all rows without) a question mark symbol in any column. I also want to change the elements to <strong>float</strong> type.</p>

<p><strong>Input:</strong></p>

<pre><code>X Y Z
0 1 ?
1 2 3
? ? 4
4 4 4
? 2 5
</code></pre>

<p><strong>Output:</strong></p>

<pre><code>X Y Z
1 2 3
4 4 4
</code></pre>

<p>Preferably using pandas dataframe operations.</p>