1. Introduction to Computing Using Python for loop / def- ining a new function  Execution control structures ( if, for, function call)  def -ining a new function  Passing and using function parameters  return- ing a value from a function

2. Introduction to Computing Using Python Function calls and execution control A function call is another kind of statement that alters the order in which statements in a program are executed A function call creates a temporary ‘excursion,’ causing the sequence of execution to jump to the named function. When the function exits, execution returns to the point where the function call occurred. We've already seen these built-in function calls: len(), type(), min(), max(), str(), bool(),... Today we are going to learn how to write our own functions how to specify what parameters are passed to our functions how to return information from functions

3. Introduction to Computing Using Python Defining a new function We have seen these calls to built-in functions: abs(), max(), len(), sum(), print() You can define a new function using def def iSquaredPlus10(x): result = x**2 + 10 return result def iSquaredPlus10(x): result = x**2 + 10 return result def : function definition keyword iSquaredPlus10 : name of function x : variable name for input argument return : specifies the value that the function returns (default: None) >>> abs(-9) 9 >>> max(2, 4) 4 >>> lst = [2,3,4,5] >>> len(lst) 4 >>> sum(lst) 14 >>> print() >>> def iSquaredPlus10(x): result = x**2 + 10 return result >>> f(1) 11 >>> f(3) 19 >>> f(0) 10 >>> abs(-9) 9 >>> max(2, 4) 4 >>> lst = [2,3,4,5] >>> len(lst) 4 >>> sum(lst) 14 >>> print() >>> def iSquaredPlus10(x): result = x**2 + 10 return result >>> f(1) 11 >>> f(3) 19 >>> f(0) 10

4. Introduction to Computing Using Python print() versus return def iSquaredPlus10(x): result = x**2 + 10 return result squarePlusTen = iSquaredPlus10(5) print(squarePlusTen) def iSquaredPlus10(x): result = x**2 + 10 return result squarePlusTen = iSquaredPlus10(5) print(squarePlusTen) def iSquaredPlus10 (x): result = x**2 + 10 print(result) def iSquaredPlus10 (x): result = x**2 + 10 print(result) return returns the sequence of execution to the point of where the function is called and (optionally) sends a value (which can be any type) back to the function call. Function returns value of res which can then be used in an expression Function prints value of res but does not return anything print() sends text to the screen. Execution proceeds to the next line of code.

5. Introduction to Computing Using Python Defining a new function def ( ): def ( ): a b c >>> hyp(3,4) 5.0 >>> >>> hyp(3,4) 5.0 >>> The general format of a function definition is Let’s develop function hyp() that: Takes two numbers as input (side lengths a and b of above right triangle ) Returns the length of the hypotenuse c import math def hyp(a, b): result = math.sqrt(a**2 + b**2) return result import math def hyp(a, b): result = math.sqrt(a**2 + b**2) return result

6. Introduction to Computing Using Python Exercise >>> hello('Julie') Welcome, Julie, to the world of Python. >>> >>> hello('Julie') Welcome, Julie, to the world of Python. >>> def hello(name): Write function hello() that: takes a name (i.e., a string) as input prints a personalized welcome message Note that the function does not return anything def hello(name): line = 'Welcome, ' + name + ', to the world of Python.’ def hello(name): line = 'Welcome, ' + name + ', to the world of Python.’ def hello(name): line = 'Welcome, ' + name + ', to the world of Python.' print(line) def hello(name): line = 'Welcome, ' + name + ', to the world of Python.' print(line)

7. Introduction to Computing Using Python Exercise >>> oddCount([4, 0, 1, -2]) 1 >>> >>> oddCount([4, 0, 1, -2]) 1 >>> def rng(lst): Write function oddCount() that: takes a list of numbers as input returns the number of odd numbers in the list def rng(lst): res = max(lst) - min(lst) def rng(lst): res = max(lst) - min(lst) def oddCount(lst): count = 0 for i in lst: if i%2 == 1: count += 1 # same as count = count+1 return count def oddCount(lst): count = 0 for i in lst: if i%2 == 1: count += 1 # same as count = count+1 return count

8. Introduction to Computing Using Python Comments and docstrings Python programs should be documented So the program’s ‘mission’ is well defined So the developer who writes/maintains the code understands it So the user knows what the program does Comments def iSquaredPlus10(x): result = x**2 + 10 # compute result return res # and return it def iSquaredPlus10(x): result = x**2 + 10 # compute result return res # and return it def f(x): 'returns x**2 + 10' res = x**2 + 10 # compute result return res # and return it def f(x): 'returns x**2 + 10' res = x**2 + 10 # compute result return res # and return it Docstring >>> help(iSquaredPlus10) Help on function iSquaredPlus10 in module __main__: iSquaredPlus10(x) >>> def iSquaredPlus10 (x): 'returns x**2 + 10' result = x**2 + 10 return result >>> help(iSquaredPlus10) Help on function iSquaredPlus10 in module __main__: iSquaredPlus10(x) returns x**2 + 10 >>> help(iSquaredPlus10) Help on function iSquaredPlus10 in module __main__: iSquaredPlus10(x) >>> def iSquaredPlus10 (x): 'returns x**2 + 10' result = x**2 + 10 return result >>> help(iSquaredPlus10) Help on function iSquaredPlus10 in module __main__: iSquaredPlus10(x) returns x**2 + 10