Lecture on First-Class Functions in Python

Overview of First-Class Functions

• Functions in Python are considered first-class citizens.
  • Can be assigned to variables.
  • Can be returned from other functions.
  • Can be stored in data structures like lists or tuples.
• Use the function name without parentheses to assign or pass functions.

Assigning Functions to Variables

• Example: Assigning a function to a variable
  • Assign a written function to variable var.
  • Call the function via the variable by passing required arguments.
  • Example: var(foo, bar) stores the return value in variable x.

Function Parameters

• Functions can have parameters that are other functions.
  • A function parameter can be called from inside another function.
  • Allows a function to change behavior based on function arguments.

Example: Function with Function Parameters

• Sheep Function
  • Declares a parameter sound_function.
  • Calls sound_function and stores the return value in sound.
  • Prints the sound.
• Main Function
  • Calls sheep function with different sound functions.
  • Prints different sheep sounds based on the function passed.
  • Functions passed: bah, ram, u.

Demonstrating Assigning and Using Functions

• Assign built-in functions to variables.
  • Example: Assign print to x and call with x('Hello').
  • Similarly, assign input to y and handle input with y().

Writing a Program with Function Parameters

• Example program with three functions returning sheep sounds.
  • Write sheep function to accept sound function as parameter.
  • Note: Use parentheses only when calling functions.
• Test sheep function with sound functions:
  • Results:
    • Call with bah: Prints "The sheep says bah".
    • Call with ram: Prints "The sheep says ram".
    • Call with u: Prints "The sheep says u".

Extending the Functionality

• Add a new function without altering sheep function.
  • Call sheep with hi_there function.
  • Demonstrates flexibility - prints message based on passed function.

Conclusion

• Function parameters allow altering behavior of functions.
• A single function can produce multiple outputs based on the passed function parameter.
• Demonstrates Python's flexibility and power with first-class functions.