This document provides an introduction to Python programming concepts such as variables, data types, strings, lists, dictionaries, conditionals, loops, functions and modules. It covers Python basics like formatting, naming conventions and comments. Key concepts are explained through examples, such as how to define and modify variables and different data structures, perform string operations, take user input, and define reusable functions. The document is intended to teach Python fundamentals to new programmers.

1. Python
BASICS
Introduction to Python programming, basic
concepts: formatting, naming conventions,
variables, etc.

2. #include <stdio.h>
int main()
{
printf("Hello, world!");
return 0;
}
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3. print "Hello, world!"
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4. # this will print "Hello, world!"
print "Hello, world!"
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inline comment

5. Keywords
• and
• del
• from
• not
• while
• as
• elif
• global
• or
• with
• assert
• else
• if
• pass
• yield
• break
• except
• import
• print
• class
• exec
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• in
• raise
• continue
• finally
• is
• return
• def
• for
• lambda
• try

6. Variables
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language_name = "Python"
naming convention: joined_lower
this is a string

7. Variables
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language_name = "Python"
version = '2.7.11'
introduced = 1991
is_awesome = True

8. Type Inference
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language_name = "Python" # string
version = '2.7.11' # another string
introduced = 1991 # integer
is_awesome = True # boolean
actual type can be checked with type()
play_with_types.py

9. String
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some_string = "I'm a string"
another_string = 'I'm a string, too'

10. String
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some_string = "I'm a string"
another_string = 'I'm a string, too'
# SyntaxError: invalid syntax

11. String
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another_string = 'I am a string, too'
another_strig = 'I'm a string, too'
escape sequence

12. String
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long_string = """I am a long string.
I span over two lines."""
long_string = '''I am another long
string.
I span over three lines.
I am composed by three sentences.'''

13. If Statement
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people = 20
cats = 30
if people < cats:
print "Too many cats! We are doomed!"
if people > cats:
print "Not many cats! We are safe!"
4 spaces
4 spaces

14. If Statement
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people = 20
cats = 30
if people < cats:
print "Too many cats! We are doomed!"
elif people > cats:
print "Not many cats! We are safe!"
else:
print "We can't decide."

15. Comparators and Booleans
Operators
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print 2 == 1
print 'string' == "string"
print not False
print 2==1 and True
print 2==1 or True

16. Comparators and Booleans
Operators
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print 2 == 1 # False
print 'string' == "string" # True
print not False # True
print 2==1 and True # False
print 2==1 or True # True

17. Characters
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for char in "hello":
print char
h
e
l
l
o

18. Characters
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say_hello = "hello!"
print say_hello[1]
e
index

19. Characters
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say_hello = "hello!"
print type(say_hello[1])
<type 'str'>

20. Combining Strings
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language_name = "Python"
version = '2.7.11'
python_version = language_name + version
# python_version is Python2.7.11
print "my " + "name" # my name
concatenation

21. Combining Strings
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language_name = "Python"
a_lot_of_python = language_name*3
# a_lot_of_python is PythonPythonPython
repetition

22. Building Complex Strings
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a = 3
b = 5
# 3 times 5 is 15
print a, "times", b, "is", a*b
works with print, only

23. Building Complex Strings
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a = 3
b = 5
# 3 times 5 is 15
result = a + " times " + b + " is " + a*b

24. Building Complex Strings
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a = 3
b = 5
# 3 times 5 is 15
result = a + " times " + b + " is " + a*b
#TypeError: unsupported operand type(s)

25. Building Complex Strings
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a = 3
b = 5
# 3 times 5 is 15
result = str(a) + " times " + str(b) + "
is " + str(a*b)

26. String Interpolation
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a = 3
b = 5
# 3 times 5 is 15
result = "%d times %d is %d" %(a, b, a*b)
Specifiers
• %s, format strings
• %d, format numbers
• %r, raw representation
tuplespecifiers.py

27. String Interpolation
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a = 3
b = 5
# 3 times 5 is 15
result = "{} times {} is {}".format(a, b,
a*b)
new way!

28. String Immutability
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# hello
say_hello = "helko"
# ops…
say_hello[3] = "l"

29. String Immutability
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# hello
say_hello = "helko"
# ops…
say_hello[3] = "l"
# TypeError

30. String Immutability
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# hello
say_hello = "helko"
# ops…
say_hello = "hello"
Other operations with strings? Python docs

31. Getting Input
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print "How old are you?"
age = raw_input() # age is a string
print "You are " + age + " years old"

32. Getting Input
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print "How old are you?"
age = raw_input() # age is a string
print "You are " + age + " years old"
# I want "age" to be a number!
age = int(raw_input())

33. Getting Input
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age = raw_input("How old are you? ")
print "You are " + age + " years old"

34. List
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fruits = ["apples", "oranges", "pears"]
count = [1, 2, 3, 4, 5]
change = [1, "pennies", 2, "dimes"]
a datatype to store multiple items, in sequence

35. Dictionary
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legs = {"ant": 6, "snake": 0, "cow": 4}
states = {"Italy": "IT", "Germany": "DE"}
a datatype to store multiple items, not in sequence
key, immutable
value

36. Loops
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doctor = 1
while doctor <= 13:
exterminate(doctor)
doctor += 1

37. For Loop: Strings
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for char in "hello":
print char
h
e
l
l
o

38. For Loop: Ranges
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for number in range(0,5):
print number
0
1
2
3
4

39. For Loop: Ranges
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for number in range(0,25,5):
print number
0
5
10
15
20

40. For Loop: Lists
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fruits = ["apples", "oranges", "pears"]
for fruit in fruits:
print "I love", fruit
I love apples
I love oranges
I love pears

41. For Loop: Dictionaries
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legs = {"ant": 6, "snake": 0, "cow": 4}
for (animal, number) in legs.items():
print "{} has {} legs".format(animal,
number)
ant has 6 legs
snake has 0 legs
cow has 4 legs

42. Printing a List
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to_buy = ["eggs", "milk"]
print to_buy
['eggs', 'milk']

43. Printing a List
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to_buy = ["eggs", "milk"]
print to_buy[0]
eggs

44. Modifying a List
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to_buy = ["eggs", "milk"]
print to_buy[0]
to_buy[0] = "butter"
print to_buy[0]
eggs
butter

45. Modifying a List
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to_buy = ["eggs", "milk"]
# I need to buy chocolate!
to_buy.append("chocolate")
['eggs', 'milk', 'chocolate']

46. Modifying a List
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to_buy = ["eggs", "milk"]
to_buy.append("chocolate")
to_buy.extend(["flour", "cheese"])
['eggs', 'milk', 'chocolate', 'flour', 'cheese']

47. Modifying a List
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to_buy = ["eggs", "milk"]
to_buy.append("chocolate")
to_buy = to_buy + ["flour", "cheese"]
['eggs', 'milk', 'chocolate', 'flour', 'cheese']
concatenation

48. Modifying a List
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to_buy = ["eggs", "milk", "chocolate",
"flour", "cheese"]
print to_buy[1:3]
['milk', 'chocolate']
slice operator

49. Modifying a List
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to_buy = ["eggs", "milk", "chocolate",
"flour", "cheese"]
# make a full copy of the list
remember = to_buy[:]
works with strings, too

50. Modifying a List
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to_buy = ["eggs", "milk", "chocolate",
"flour", "cheese"]
# I don't need cheese!
to_buy.pop()
# … neither milk, by the way!
to_buy.pop(1)

51. Modifying a List
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to_buy = ["eggs", "milk", "chocolate",
"flour", "cheese"]
# I don't need cheese!
to_buy.remove("cheese")
# … neither milk, by the way!
to_buy.remove("milk")

52. Modifying a List
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to_buy = ["eggs", "milk", "chocolate",
"flour", "cheese"]
# I want my original list back!
del to_buy[2:6]
['eggs', 'milk']

53. Strings vs. Lists
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A string is a sequence of characters…
… but a list of characters is not a string
language_name = "Python"
# string to list
name = list(language_name)

54. Strings vs. Lists
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sentence = "this is AmI"
# break a string into separate words
words = sentence.split()
['this', 'is', 'AmI']

55. Copying Lists
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fruits = ['apple', 'orange']
favorite_fruits = fruits
# add a fruit to the original list
fruits.append('banana')
print 'The fruits now are:', fruits
print 'My favorite fruits are', favorite_fruits
Fruits are: ['apple', 'orange', 'banana']
My favorite fruits are: ['apple', 'orange',
'banana']
???

56. Copying Lists
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fruits = ['apple', 'orange']
favorite_fruits = fruits
# add a fruit to the original list
fruits.append('banana')
print 'The fruits now are:', fruits
print 'My favorite fruits are', favorite_fruits
We do not make a copy of
the entire list, but we only
make a reference to it!

57. Copying Lists (For Real!)
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# option 1: slice
favorite_fruits = fruits[:]
#option 2: create a new list - best!
favorite_fruits = list(fruit)
#extend an empty list
favorite_fruits.extends(fruit)
Other operations with lists? Python docs

58. Printing a Dictionary
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legs = {"ant": 6, "snake": 0 }
print legs
{'ant': 6, 'snake': 0}

59. Modifying a Dictionary
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legs = {"ant": 6, "snake": 0 }
legs["spider"] = 273
{'ant': 6, 'snake': 0, 'spider': 273}

60. Modifying a Dictionary
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legs = {"ant": 6, "snake": 0 }
legs["spider"] = 273 # basically, run!
legs["spider"] = 8 # better!
{'ant': 6, 'snake': 0, 'spider': 8}

61. Modifying a Dictionary
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legs = {"ant": 6, "snake": 0, "spider": 8}
# I don't like spiders
legs.del["spider"]
# Clear all the things!
legs.clear()

62. Retrieving a Value from a
Dictionary
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legs = {"ant": 6, "snake": 0}
# get "ant"!
legs["ant"] # 6
# get "spider"
legs["spider"]

63. Retrieving a Value from a
Dictionary
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legs = {"ant": 6, "snake": 0}
# get "ant"!
legs["ant"] # 6
# get "spider"
legs["spider"]
# KeyError: spider

64. Retrieving a Value from a
Dictionary
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legs = {"ant": 6, "snake": 0}
# check if "spider" is in the dictionary
"spider" in legs # False
# get "spider" without throwing errors
legs.get("spider") # None
# get "spider" with a custom value
legs.get("spider", "Not present")

65. Functions
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def say_hello():
print "Hello!"
say_hello()
definition
call

66. Functions with Parameters
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def say_hello_to(name):
print "Hello", name
say_hello_to("AmI students")

67. Default Parameter Values
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def say_hello_to(name="AmI"):
print "Hello", name
say_hello_to() # Hello AmI
say_hello_to("students") # Hello students

68. Returning Values
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def build_greetings(name="AmI"):
return "Hello" + name
greeting = build_greetings()
print greeting # Hello AmI

69. Returning Multiple Values
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def build_greetings(name="AmI"):
return ("Hello", name)
(greeting, person) = build_greetings()
print greeting + " to " + person
# Hello to AmI

70. Documenting Functions
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def build_greetings(name="AmI"):
'''Build a greeting in the format
Hello plus a given name'''
return ("Hello", name)
docstring

71. Modules
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• A way to logically organize the code
• They are files consisting of Python code
– they can define (and implement) functions, variables,
etc.
– typically, the file containing a module is called in the
same way
• e.g., the math module resides in a file named math.py

72. Importing a Module
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import math # import the math module
print math.pi # print 3.141592…
from math import pi # import pi, only!
print pi # print 3.141592…
from math import * # import all the names
print pi DO NOT USE

73. Command Line Parameters
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from sys import argv
script, first = argv
print "The script is called:", script
print "The parameter is:", first
> python my_script.py one
The script is called: my_script.py
The parameter is: one
unpacking

74. Reading Files
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from sys import argv
filename = argv[1]
txt = open(filename)
print "Here's your file %r:", % filename
print txt.read()
open the file
show the file content

75. Writing Files
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from sys import argv
filename = argv[1]
# open the file in write mode
target = open(filename, "w")
target.truncate() # empties the file
# write a string into the file
target.write("This is the new content")
target.close() # close the file

76. References and Links
• Python Documentation, http://docs.python.org/2
• The Python Tutorial, http://docs.python.org/2/tutorial/
• The Google Python course,
https://developer.google.com/edu/python
• Online Python Tutor, http://pythontutor.com
• «Think Python: How to think like a computer scientist»,
Allen Downey, Green Tea Press, Needham,
Massachusetts
• «Dive into Python 2», Mark Pilgrim
• «Learn Python the Hard Way», Zed Shaw
• «Learning Python» (5th edition), Mark Lutz, O'Reilly
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77. Questions?
01QZP AMBIENT INTELLIGENCE
Luigi De Russis
luigi.derussis@polito.it

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3/10/2016 Version Control with Git 78