Lecture 4 - Functions

---

1. Function syntax

Syntax  
def <function name> (<formal parameters>):
 <function body>

tips

• If the output can be either an int or a float, select num, which isn’t a real Python type, but which we’ll use to indicate that either basic numeric type is legal.

  • eg:

    def a(x):
       '''
       x: int or float.
       '''
       return x + 1 # Output is num
    

2. ENVIRONMENTS

• Environments to understand bindings

  • Environments are formalism for tracking bindings of variables and values

  • Assignments pair name and value in environment

  • Asking for value of name just looks up in current environment •

  • Python shell is default (or global) environment

  • Definitions pair function name with details of function

• COMPUTING POWERS AS AN EXAMPLE

  • Example of computation without and with functional abstraction

        ## Example of computation without and with functional abstraction

            ## Without functional abstraction

            ##x = raw_input('Enter a number: ')
            ##p = int(raw_input('Enter an integer power: '))
            ##
            ##result = 1
            ##
            ##for turn in range(p):
            ##    print('iteration: ' + str(turn) + ' current result: ' + str(result))
            ##    result = result * x


            ## With functional abstraction

            def iterativePower(x,p):
                result = 1
                for turn in range(p):
                    print ('iteration: ' + str(turn) + ' current result: ' + str(result))
                    result = result * x
                return result

3.UNDERSTANDING VARIABLE BINDING

• Each function call creates a new environment, which scopes bindings of formal parameters
  and values, and of local variables (those created with assignments within body)
• Scoping often called static or lexical because scope within which variable has value is
  defined by extent of code boundaries.

4. Using function modules

• steps:

  • Place in a XX.py file

  • Use import command to access
    example:

    
    # circle.py
    
    
    # From Lecture 4, Modules
    
    
    pi = 3.14159
    
    def area(radius):
        return pi*(radius**2)
    
    def circumference(radius):
        return 2*pi*radius

  2 ways:

  • import circle

  • from circle import *