Lecture-20 Parameter Return 24-25

COMP101 Introduction to Programming 2024-25 Lecture-20

• Focus: Parameter Return

Calling Functions – No Value Returned

• Function without Return

  • No arguments or parameters; solely operates on internal data.

  • Data within the function is local and cannot be accessed outside of it.

• Function with Argument but No Return

  • A copy of the data is passed into the function.

  • Data remains local and restricted to the function's scope.

Value Not Returned to Caller

• Example Function Definition

  def num_length(number_str):  
      length_of_num = len(number_str)  
      print("Your number has", length_of_num, "digits in it")  
      return  

• Key Points:

  • length_of_num is a local variable within num_length.

  • number_str is also a local variable received as a parameter.

  • Local variables are bound by the function's scope and cannot be accessed externally.

  • Using return with no value effectively returns None (it’s good practice to use it).

Calling Functions - Value Returned

• Function with Argument and Return:

  • When a function is called with an argument, the parameter becomes a local variable.

  • The function can modify and return the value of the local variable.

  • The return statement is typically the last line within the function.

Value Returned to Caller

• Function Call Steps:

  1. Call the function using a variable as an argument.

  2. The variable captures the returned value from the function.

  3. Inside the function, the parameter is used for operations.

  4. Use return(parameter_name) to send the value back to the caller.

Example of Returning a Value

• Function Definition:

  def squared(value):  
      value = value * value  
      return value  

• In Main Function:

  def main():  
      num = 5  
      num_squared = squared(num)  
      print(num_squared)  

• Explanation of Execution:

  • num_squared captures the result of squared.

  • value inside squared is local to that function.

  • The returned value from squared is captured and can be printed, resulting in 25.

  • The original num remains unaffected, demonstrating that a copy of the argument is passed.

Example of Average Calculation

• Function Definition:

  def myGrades(a, b, c, d):  
      average = (a + b + c + d) / 4  
      return average  

• Main Function Calculation:

  def main():  
      ca01, ca02, ca03, ca04 = 9, 20, 34, 45  
      finalScore = myGrades(ca01, ca02, ca03, ca04)  
      print("Average of scores =", finalScore)  

• Details:

  • Average calculated within myGrades returns to finalScore.

  • The original grades remain unchanged outside the function.

Passing Arguments - General

• Call-by-Value:

  • A copy of the argument is supplied to the function.

  • Changes inside the function do not affect the original value.

• Call-by-Reference (Path Types):

  • The function can access the original variable’s memory location.

  • Original values may be modified within the function, affecting them externally.

Python - How it Passes Arguments

• Argument Passing in Python:

  • Python utilizes assignment for argument passing.

  • Data types determine whether Python uses call-by-value or call-by-reference methodology.

• Immutable vs. Mutable Objects:

  • Immutable (numbers, strings, tuples): Passed by value.

  • Mutable (lists, dictionaries): Passed by reference.