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      Positional-Only Arguments

      Python Tutorial

      This Python tutorial has been written for the beginners to help them understand the basic to advanced concepts of Python Programming Language. After completing this tutorial, you will find yourself at a great level of expertise in Python, from where you can take yourself to the next levels to become a world class Software Engineer.

      Positional-Only Arguments

      It is possible in Python to define a function in which one or more arguments can not accept their value with keywords. Such arguments may be called positional-only arguments.
      Python's built-in input() function is an example of positional-only arguments. The syntax of input function is
      input(prompt = "")
      Prompt is an explanatory string for the benefit of the user. For example
      name = input("enter your name ")
      However, you cannot use the prompt keyword inside the parantheses.
         name = input (prompt="Enter your name ")
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      TypeError: input() takes no keyword arguments
      To make an argument positional-only, use the "/" symbol. All the arguments before this symbol will be treated as position-only.

      Example

      We make both the arguments of intr() function as positional-only by putting "/" at the end.
      def intr(amt, rate, /):
         val = amt*rate/100
         return val
      If we try to use the arguments as keywords, Python raises following error message
         interest = intr(amt=1000, rate=10)
                    ^^^^^^^^^^^^^^^^^^^^^^^
      TypeError: intr() got some positional-only arguments passed as keyword arguments: 'amt, rate'
      A function may be defined in such a way that it has some keyword-only and some positional-only arguments.
      def myfunction(x, /, y, *, z):
         print (x, y, z)
      In this function, x is a required positional-only argument, y is a regular positional argument (you can use it as keyword if you want), and z is a keyword-only argument.
      The following function calls are valid
      myfunction(10, y=20, z=30)
      myfunction(10, 20, z=30)
      However, these calls raise errors
         myfunction(x=10, y=20, z=30)
      TypeError: myfunction() got some positional-only arguments passed as keyword arguments: 'x'
      
         myfunction(10, 20, 30)
      TypeError: myfunction() takes 2 positional arguments but 3 were given

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.