pandas, multiply all the numeric values in the data frame by a constant
<p>How to multiply all the numeric values in the data frame by a constant without having to specify column names explicitly? Example:</p>

<pre><code>In [13]: df = pd.DataFrame({'col1': ['A','B','C'], 'col2':[1,2,3], 'col3': [30, 10,20]})

In [14]: df
Out[14]: 
  col1  col2  col3
0    A     1    30
1    B     2    10
2    C     3    20
</code></pre>

<p>I tried <code>df.multiply</code> but it affects the string values as well by concatenating them several times.</p>

<pre><code>In [15]: df.multiply(3)
Out[15]: 
  col1  col2  col3
0  AAA     3    90
1  BBB     6    30
2  CCC     9    60
</code></pre>

<p>Is there a way to preserve the string values intact while multiplying only the numeric values by a constant? </p>