IoT Heaps 4

Chapter 6
IoT Systems –
Logical Design using Python

Outline
• Introduction to Python
• Installing Python
• Python data types and data structures
• Control flow
• Functions
• Modules
• Packages
• File input/output
• Date/Time operations
• Classes

Python
• Python is a general-purpose high-level programming language suitable for providing a solid
foundation to the reader in the area of cloud computing.
The main characteristics of Python are:
• Multi-paradigm programming language
• Python supports more than one programming paradigm, including object-oriented programming and structured
programming
• Interpreted language
• Python is an interpreted language and does not require an explicit compilation step. The Python interpreter
executes the program source code directly, statement by statement, as a processor or scripting engine does.
• Interactive language
• Python provides an interactive mode in which the user can submit commands at the Python prompt and interact
with the interpreter directly.

Python – Benefits
• Easy-to-learn, read and maintain
• Python is a minimalistic language with relatively few keywords, uses English keywords and has fewer syntactical constructions
as compared to other languages. Reading Python programs feels like reading English with pseudocode-like constructs. Python
is easy to learn yet an extremely powerful language for a wide range of applications.
• Object and procedure oriented
• Python supports both procedure-oriented programming and object-oriented programming. Procedure-oriented paradigm
allows programs to be written around procedures or functions that allow reuse of code. Object-oriented paradigm allows
programs to be written around objects that include both data and functionality.
• Extendable
• Python is an extendable language and allows integration of low-level modules written in languages such as C/C++. This is useful
when you want to speed up a critical portion of a program.
• Scalable
• Due to the minimalistic nature of Python, it provides a manageable structure for large programs.
• Portable
• Since Python is an interpreted language, programmers do not have to worry about compilation, linking and loading of
programs. Python programs can be directly executed from the source.
• Broad library support
• Python has broad library support and works on various platforms such as Windows, Linux, Mac, etc.

Python – Setup
• Windows
• Python binaries for Windows can be downloaded from http://www.python.org/getit
• For the examples and exercise in this book, you would require Python 2.7 which can be downloaded directly from
http://www.python.org/ftp/python/2.7.5/python-2.7.5.msi
• Once the python binary is installed, you can run the python shell at the command prompt using
> python
• Linux
#Install Dependencies
sudo apt-get install build-essential
sudo apt-get install libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev
#Download Python
wget http://python.org/ftp/python/2.7.5/Python-2.7.5.tgz
tar -xvf Python-2.7.5.tgz
cd Python-2.7.5
#Install Python
./configure
make
sudo make install

Numbers
• Numbers
• The number data type is used to store numeric values. Numbers are immutable data types, therefore changing the value of a number
data type results in a newly allocated object.
#Integer
>>>a=5
>>>type(a)
<type ’int’>
#Floating Point
>>>b=2.5
>>>type(b)
<type ’float’>
#Long
>>>x=9898878787676L
>>>type(x)
<type ’long’>
#Complex
>>>y=2+5j
>>>y
(2+5j)
>>>type(y)
<type ’complex’>
>>>y.real
2
>>>y.imag
5
#Addition
>>>c=a+b
>>>c
7.5
>>>type(c)
<type ’float’>
#Subtraction
>>>d=a-b
>>>d
2.5
>>>type(d)
<type ’float’>
#Multiplication
>>>e=a*b
>>>e
12.5
>>>type(e)
<type ’float’>
#Division
>>>f=b/a
>>>f
0.5
>>>type(f)
<type float’>
#Power
>>>g=a**2
>>>g
25

Strings
• Strings
• A string is simply a list of characters in order. There are no limits to the number of characters you can have in a string.
#Create string
>>>s="Hello World!"
>>>type(s)
<type ’str’>
#String concatenation
>>>t="This is sample program."
>>>r = s+t
>>>r
’Hello World!This is sample program.’
#Get length of string
>>>len(s)
12
#Convert string to integer
>>>x="100"
>>>type(s)
<type ’str’>
>>>y=int(x)
>>>y
100
#Print string
>>>print s
Hello World!
#Formatting output
>>>print "The string (The string (Hello World!) has
12 characters
#Convert to upper/lower case
>>>s.upper()
’HELLO WORLD!’
>>>s.lower()
’hello world!’
#Accessing sub-strings
>>>s[0]
’H’
>>>s[6:]
’World!’
>>>s[6:-1]
’World’
#strip: Returns a copy of the string with the
#leading and trailing characters removed.
>>>s.strip("!")
’Hello World’

Lists
• Lists
• A list is a compound data type used to group together other values. List items need not all be of the same type. A list contains items
separated by commas and enclosed within square brackets.
#Create List
>>>fruits=[’apple’,’orange’,’banana’,’mango’]
>>>type(fruits)
<type ’list’>
#Get Length of List
>>>len(fruits)
4
#Access List Elements
>>>fruits[1]
’orange’
>>>fruits[1:3]
[’orange’, ’banana’]
>>>fruits[1:]
[’orange’, ’banana’, ’mango’]
#Appending an item to a list
>>>fruits.append(’pear’)
>>>fruits
[’apple’, ’orange’, ’banana’, ’mango’, ’pear’]
#Removing an item from a list
>>>fruits.remove(’mango’)
>>>fruits
[’apple’, ’orange’, ’banana’, ’pear’]
#Inserting an item to a list
>>>fruits.insert(1,’mango’)
>>>fruits
[’apple’, ’mango’, ’orange’, ’banana’, ’pear’]
#Combining lists
>>>vegetables=[’potato’,’carrot’,’onion’,’beans’,’r
adish’]
>>>vegetables
[’potato’, ’carrot’, ’onion’, ’beans’, ’radish’]
>>>eatables=fruits+vegetables
>>>eatables
[’apple’, ’mango’, ’orange’, ’banana’, ’pear’,
’potato’, ’carrot’, ’onion’, ’beans’, ’radish’]
#Mixed data types in a list
>>>mixed=[’data’,5,100.1,8287398L]
>>>type(mixed)
<type ’list’>
>>>type(mixed[0])
<type ’str’>
>>>type(mixed[1])
<type ’int’>
>>>type(mixed[2])
<type ’float’>
>>>type(mixed[3])
<type ’long’>
#Change individual elements of a list
>>>mixed[0]=mixed[0]+" items"
>>>mixed[1]=mixed[1]+1
>>>mixed[2]=mixed[2]+0.05
>>>mixed
[’data items’, 6, 100.14999999999999, 8287398L]
#Lists can be nested
>>>nested=[fruits,vegetables]
>>>nested
[[’apple’, ’mango’, ’orange’, ’banana’, ’pear’], [’potato’,
’carrot’, ’onion’, ’beans’, ’radish’]]

Tuples
• Tuples
• A tuple is a sequence data type that is similar to the list. A tuple consists of a number of values separated by commas and enclosed
within parentheses. Unlike lists, the elements of tuples cannot be changed, so tuples can be thought of as read-only lists.
#Create a Tuple
>>>fruits=("apple","mango","banana","pineapple")
>>>fruits
(’apple’, ’mango’, ’banana’, ’pineapple’)
>>>type(fruits)
<type ’tuple’>
#Get length of tuple
>>>len(fruits)
4
#Get an element from a tuple
>>>fruits[0]
’apple’
>>>fruits[:2]
(’apple’, ’mango’)
#Combining tuples
>>>vegetables=(’potato’,’carrot’,’onion’,’radish’)
>>>eatables=fruits+vegetables
>>>eatables
(’apple’, ’mango’, ’banana’, ’pineapple’, ’potato’, ’carrot’, ’onion’, ’radish’)

Dictionaries
• Dictionaries
• Dictionary is a mapping data type or a kind of hash table that maps keys to values. Keys in a dictionary can be of any data type, though
numbers and strings are commonly used. The values in a dictionary can be any data type or object.
#Create a dictionary
>>>student={’name’:’Mary’,’id’:’8776’,’major’:’CS’}
>>>student
{’major’: ’CS’, ’name’: ’Mary’, ’id’: ’8776’}
>>>type(student)
<type ’dict’>
#Get length of a dictionary
>>>len(student)
3
#Get the value of a key in dictionary
>>>student[’name’]
’Mary’
#Get all items in a dictionary
>>>student.items()
[(’gender’, ’female’), (’major’, ’CS’), (’name’, ’Mary’),
(’id’, ’8776’)]
#Get all keys in a dictionary
>>>student.keys()
[’gender’, ’major’, ’name’, ’id’]
#Get all values in a dictionary
>>>student.values()
[’female’, ’CS’, ’Mary’, ’8776’]
#Add new key-value pair
>>>student[’gender’]=’female’
>>>student
{’gender’: ’female’, ’major’: ’CS’, ’name’: ’Mary’, ’id’:
’8776’}
#A value in a dictionary can be another dictionary
>>>student1={’name’:’David’,’id’:’9876’,’major’:’ECE’}
>>>students={’1’: student,’2’:student1}
>>>students
{’1’: {’gender’: ’female’, ’major’: ’CS’, ’name’: ’Mary’, ’id’:
’8776’}, ’2’: {’
major’: ’ECE’, ’name’: ’David’, ’id’: ’9876’}}
#Check if dictionary has a key
>>>student.has_key(’name’)
True
>>>student.has_key(’grade’)
False

Type Conversions
#Convert to string
>>>a=10000
>>>str(a)
’10000’
#Convert to int
>>>b="2013"
>>>int(b)
2013
#Convert to float
>>>float(b)
2013.0
#Convert to long
>>>long(b)
2013L
#Convert to list
>>>s="aeiou"
>>>list(s)
[’a’, ’e’, ’i’, ’o’, ’u’]
#Convert to set
>>>x=[’mango’,’apple’,’banana’,’mango’,’banana’]
>>>set(x)
set([’mango’, ’apple’, ’banana’])
• Type conversion examples

Control Flow – if Statement
• The if statement in Python is similar to the if statement in other languages.
>>>a = 25**5
>>>if a>10000:
print "More"
else:
print "Less"
More
>>>s="Hello World"
>>>if "World" in s:
s=s+"!"
print s
Hello World!
>>>if a>10000:
if a<1000000:
print "Between 10k and 100k"
else:
print "More than 100k"
elif a==10000:
print "Equal to 10k"
else:
print "Less than 10k"
More than 100k
>>>student={’name’:’Mary’,’id’:’8776’}
>>>if not student.has_key(’major’):
student[’major’]=’CS’
>>>student
{’major’: ’CS’, ’name’: ’Mary’, ’id’: ’8776’}

Control Flow – for Statement
• The for statement in Python iterates over items of any sequence (list, string, etc.) in the order in which they
appear in the sequence.
• This behavior is different from the for statement in other languages such as C, in which initialization,
incrementing and stopping criteria are provided.
#Looping over characters in a string
helloString = "Hello World"
for c in helloString:
print c
#Looping over keys in a dictionary
student = ’name’: ’Mary’, ’id’: ’8776’,’gender’:
’female’, ’major’: ’CS’
for key in student:
print "%s: %s" % (key,student[key]
#Looping over items in a list
fruits=[’apple’,’orange’,’banana’,’mango’]
i=0
for item in fruits:
print "Fruit-%d: %s" % (i,item)
i=i+1

Control Flow – while Statement
• The while statement in Python executes the statements within the while loop as long as the condition is true.
#Prints even numbers upto 100
>>> i = 0
>>> while i<=100:
if i%2 == 0:
print i
i = i+1

Control Flow – range Statement
• The range statement in Python generates a list of numbers in arithmetic progression.
#Generate a list of numbers from 10 - 100 with increments
of 10
>>>range(10,110,10)
[10, 20, 30, 40, 50, 60, 70, 80, 90,100]
#Generate a list of numbers from 0 – 9
>>>range (10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Control Flow – break/continue Statements
• The break and continue statements in Python are similar to the statements in C.
• break
• The break statement breaks out of the for/while loop
• continue
• The continue statement continues with the next iteration.
#Continue statement example
>>>fruits=[’apple’,’orange’,’banana’,’mango’]
>>>for item in fruits:
if item == "banana":
continue
else:
print item
apple
orange
mango
#Break statement example
>>>y=1
>>>for x in range(4,256,4):
y = y * x
if y > 512:
break
print y
4
32
384

Control Flow – pass Statement
• The pass statement in Python is a null operation.
• The pass statement is used when a statement is required syntactically but you do not want any command or
code to execute.
>fruits=[’apple’,’orange’,’banana’,’mango’]
>for item in fruits:
if item == "banana":
pass
else:
print item
apple
orange
mango

Functions – Passing by Reference
• All parameters in Python functions are passed by reference.
• If a parameter is changed within a function, the change is also reﬂected in the calling function.
>>>def displayFruits(fruits):
print "There are %d fruits in the list" % (len(fruits))
for item in fruits:
print item
print "Adding one more fruit"
fruits.append('mango')
>>>fruits = ['banana', 'pear', 'apple']
>>>displayFruits(fruits)
There are 3 fruits in the list
banana
pear
apple
#Adding one more fruit
>>>print "There are %d fruits in the list" % (len(fruits))
There are 4 fruits in the list

IoT Heaps 4

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