title: Removing left brackets at beginning and end of column values throughout dataframe
body: <p>I have a dataframe with columns that have values in this format: [0.0, 0.2[</p>
  <p>Yes, those are two left brackets.  I've removed them once by using an iterative loop, .iloc, .rpartition, and .apply; however, I'm hoping there's a one-liner out there that can help me remove all of them from the entire dataframe.</p>
  <p>I tried <code>df[cols_to_check] = df[cols_to_check].replace({&quot;[&quot;:&quot;&quot;}, regex=True)</code>, but I receive this error:</p>
  <p>error: unterminated character set at position 0</p>
  <p>I suspect this is because '[' is a special character.</p>
  <p>Here's a sample dataframe:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th style="text-align: right;">district_id</th>
  <th style="text-align: center;">pct_black_hisp</th>
  <th style="text-align: center;">pct_free_red</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td style="text-align: right;">1234</td>
  <td style="text-align: center;">[0.2, 0.4[</td>
  <td style="text-align: center;">[0.0, 0.2[</td>
  </tr>
  <tr>
  <td style="text-align: right;">2468</td>
  <td style="text-align: center;">NaN</td>
  <td style="text-align: center;">[0.4, 0,8[</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>district_id is an int, the other columns are objects.</p>