title: takes 0 positional arguments but 1 was given or missing 1 required positional argument: 'radius' depending on how I write the code
body: <p>This is what I have so far.</p>
  
  <pre><code># This program uses a value returning function named circle
  # that takes the radius of a circle and returns the area and the
  # circumference of the circle.
  
  #####################################
  # Start program
  # Main()
  # Get user input of radius from user. 
  # Pass argument radius to circle function
  # circle()
  # Calculate circumference
  # Calculate area
  # Return values from circle to main
  # Main()
  # Print circumference 
  # Print area
  # End program
  #####################################
  
  # First we must import the math functions
  import math
  
  # Start of program
  def main():
      # Get circle's radius from user
      radius=float(input('Enter the radius of the circle: '))
  
      #Calling the circle funcion while passing radius to it
      circle(radius)
  
      #Gathering returned results from circle function
      circumference, area = circle()
  
      #Printing results
      print('Circle circumference is ', circumference)
      print('Circle area is ', area)
  
  # Circle function
  def circle(radius):
  
      # Returning results to main 
      return 2 * math.pi * radius, math.pi * radius**2
  
  # End program
  main()
  </code></pre>
  
  <p>But I get this error:</p>
  
  <blockquote>
    <p>Enter the radius of the circle: 2 Traceback (most recent call last):<br>
    File "/Users/shawnclark/Documents/ Introduction to Computer
    Programming/Chapter 05/Assignment/5.1.py", line 45, in 
        main()   File "/Users/shawnclark/Documents/ Introduction to Computer Programming/Chapter 05/Assignment/5.1.py", line 32, in main
        circumference, area = circle() TypeError: circle() missing 1 required positional argument: 'radius'</p>
  </blockquote>