title: 'str' object has no attribute
body: <p>I'm trying to open a column in excel and move all the values from it's cells into a list. </p>
  
  <pre><code>def open_excel(col, excel_file): 
     open_file = openpyxl.load_workbook(excel_file) 
     sheet_object = open_file.get_sheet_names()[0]
     cell_vals = []
     col_num = column_index_from_string(start_col)
     for cell in sheet_object.columns[col_num]: 
         cell_vals.append(str(cell.value))
  </code></pre>
  
  <p>After I run that I get the error: </p>
  
  <pre><code>builtins.AttributeError: 'str' object has no attribute 'columns'
  </code></pre>
  
  <p>But I've already imported everything as well. </p>
  
  <p>Here's what I've imported: </p>
  
  <pre><code>import openpyxl 
  from openpyxl.cell import get_column_letter, column_index_from_string
  import numpy as np 
  import matplotlib.pyplot as plt
  </code></pre>