title: How to get mutable string?
body: <p>I am generating sql query and perfoming a lot of += operations on my string. It looks like:</p>
  
  <pre><code>insert_string = 'INSERT INTO ' + table_name + ' VALUES '
  for row in data_frame.iterrows():
          raw_row = row[1].values
          insert_string += str(tuple(raw_row))
  </code></pre>
  
  <p>So if my insert_string are immutable every += operation creates new string. For example, in C# there is StringBuilder class for this, that could initialise empty string with given capacity. How can i do it in Python?</p>