title: Format specifier missing precision error with string formatting
body: <p>This is my code:</p>
  <pre><code>from tkinter import *
  
  def calculate():
      temp = int(entry.get())
      temp = 9/5*temp+32
      output_label.configure(text = 'Converted: {:.lf}'.format(temp))
      entry.delete(0,END)
  
  root = Tk()
  message_label = Label(text = 'Enter a temperature',
                       font=('Verdana', 16))
  output_label = Label(font = ('Verdana', 16))
  entry = Entry(font = ('Verdana', 16), width=4)
  calc_button = Button(text ='ok', font=('Verdana', 16),
                      command=calculate)
  message_label.grid(row=0, column=0)
  entry.grid(row=0, column=1)
  calc_button.grid(row=0, column=2)
  output_label.grid(row=1, column=0, columnspan=3)
  
  mainloop()
  </code></pre>
  <p>This is the output error:</p>
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File &quot;C:\Users\USER\Anaconda3\envs\nlp_course\lib\tkinter\__init__.py&quot;, line 1705, in __call__
      return self.func(*args)
    File &quot;&lt;ipython-input-9-c6af4eb59ca6&gt;&quot;, line 7, in calculate
      output_label.configure(text = 'Converted: {:.lf}'.format(temp))
  ValueError: Format specifier missing precision
  </code></pre>
  <p>Can someone help with this problem?</p>