Pandas add space between characters if needed
<p>Given the following data frame:</p>

<pre><code>import pandas as pd
import numpy as np
df = pd.DataFrame({'A':['One[P]','Two [N]'],
})

df
    A
0   One[P]
1   Two [N]
</code></pre>

<p>I'd like to add a space before the open bracket ('[') if one does not exist (for a very tall column). </p>

<p>The desired result is:</p>

<pre><code>    A
0   One [P]
1   Two [N]
</code></pre>

<p>Thanks in advance!</p>