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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
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
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: 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 + 10return result
>>> f(1)11>>> f(3)19>>> f(0)10
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 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 resbut does not return anything
print() sends text to the screen. Execution proceeds to the next line of code.
Introduction to Computing Using Python
Defining a new function
def <function name> (<0 or more variables>): <indented function body>
a
b
c
>>> 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 mathdef hyp(a, b): result = math.sqrt(a**2 + b**2) return result
Introduction to Computing Using Python
Exercise
>>> 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.' print(line)
Introduction to Computing Using Python
Exercise
>>> 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 oddCount(lst): count = 0 for i in lst: if i%2 == 1: count += 1 # same as count = count+1 return count
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 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 + 10return result
>>> help(iSquaredPlus10)Help on function iSquaredPlus10 in module __main__:
iSquaredPlus10(x) returns x**2 + 10
