An Introduction To Python and Python on the Raspberry Pi

Slides from my talk at the BrightonPi / BrightonPy “Raspberry Pi Jam” night.

Transcript

1. An Introduction To Python and Python on the Raspberry Pi Jamie Matthews Raspberry Pi Jam - “Py vs Pi” 27th November 2012
2. Agenda About me Why Python? A brief tour Python on the Raspberry Pi Python for hardware hacking Discussion?
3. BrightonPy
6. Before we start.
7. http://flic.kr/p/8JzoGv
8. http://flic.kr/p/4kzYrd
10. Python
11. Not named after this http://flic.kr/p/9pb6Zj
12. Named after this
13. (but yes, the logo is a snake)
14. PyPI Python Package Index http://pypi.python.org
15. PyPy A fast, compliant alternative implementation of the Python language http://pypy.org
16. Raspberry Pi
17. BrightonPy BrightonPi
18. Proposal: BrightonPie
19. Anyway.
20. A Brief History of Python Created by Guido van Rossum Implementation started in 1989 Python 1.0 released January 1994 Python 2.0 released October 2000 Python 3.0 released December 2008 *
21. Why Python?
22. Why Python? Emphasis on readability Widely used Batteries included (or, at least, available) Multi-paradigm
23. Readability “Programs must be written for people to read, and only incidentally for machines to execute” -H. Abelson and G. Sussman (in "The Structure and Interpretation of Computer Programs)
24. “Nobody ever got fired for choosing Python” Scientific communities Web communities Google, NASA, US government
25. Batteries included (or, at least, available)
26. Standard Library subprocess csv json sqlite3 os datetime logging smtplib multiprocessing urllib2 posix signal pickle zlib hashlib
27. Python Package Index 25k+ third-party packages
28. Plays well with others Easy to write extensions in C for speed Easy to communicate with other processes Jython, IronPython, PyPy Embeddable as a scripting language
29. Multi-paradigm
30. “Python is a scripting language”
31. Scripts “programs written for a software environment that automate the execution of tasks which could alternatively be executed one-by-one by a human operator.” - wikipedia
32. Scripts “programs written for a software environment that automate the execution of tasks which could alternatively be executed one-by-one by a human operator.” - wikipedia
33. Scripts Real programs
34. “Scripts” “Real programs”
35. Scripts Real programs
36. Scripts Real programs
37. Scripts Real programs
38. Imperative Object Oriented Functional
39. Let’s see some code (just a little)
40. Where to start 1. Open a terminal 2. Type python
43. Running code in a file 1. Create a file with a .py extension 2. Put some code in it 3. At a terminal prompt, type python yourfile.py
44. Basic types Integers: 42 Floats: 3.141 Strings: "Hello, Brighton"
45. Basic types Lists: [1, 2, 4, 8, 16] Tuples: (1, "Hello", 5.2) Dictionaries: {"greeting": "Hello", "location": "Brighton"}
46. Names x = 5 5 x Names are labels attached to things
47. Names 5 x y Names are labels attached to things x = 5 y = x
48. Control structures location = "Brighton" if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate"
49. Control structures places = ["Sussex", "Cornwall"] for place in places: print place
50. Functions def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate" greet("Brighton")
51. Classes class MyClass(object): def say_hello(self): print "Hello!" my_instance = MyClass() my_instance.say_hello()
52. Aside: significant whitespace
53. Brackety languages function greet(location) { if (location === "Brighton") { console.log("Hello, Brighton"); } else { console.log("How unfortunate"); } }
54. Python uses whitespace def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate"
55. Whitespace is significant def greet(location): !!!!if location == "Brighton": !!!!!!!!print "Hello, Brighton!" !!!!else: !!!!!!!!print "How unfortunate"
56. Whitespace is significant def greet(location): !!!!if location == "Brighton": !!!!!!!!print "Hello, Brighton!" !!!!else: !!!!!!!!!print "How unfortunate"
57. Whitespace is significant def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate" (actually, this works fine)
58. Whitespace is significant def greet(location): !!!!if location == "Brighton": !!!!!!!!print "Hello, Brighton!" !!!!else: !!!!print "How unfortunate" IndentationError: expected an indented block
59. Whitespace is boring 1. Use an editor that indents code automatically 2. Set it to indent with four spaces 3. Get on with your life Aside over
60. Using code from elsewhere Every Python file is a namespace. You can import names from other files. You can also create packages (namespaces) consisting of multiple files and import names from them.
61. def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate" greeter.py
62. def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate" from greeter import greet greeter.py anotherfile.py
63. def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate" from greeter import greet greeter.py anotherfile.py
64. def greet(location): if location == "Brighton": print "Hello, Brighton!" else: print "How unfortunate" from greeter import greet greet("Brighton") greeter.py anotherfile.py
65. A (tiny) real example
66. A (tiny) real example from urllib2 import urlopen >
67. A (tiny) real example from urllib2 import urlopen response = urlopen('http://jsonip.com/') >
68. A (tiny) real example from urllib2 import urlopen response = urlopen('http://jsonip.com/') print response.read() >
69. A (tiny) real example from urllib2 import urlopen response = urlopen('http://jsonip.com/') print response.read() {"ip":"87.xxx.xxx.xxx","about":"/about"} >
70. A (tiny) real example from urllib2 import urlopen import json response = urlopen('http://jsonip.com/') data = json.loads(response.read()) print data['ip'] >
71. A (tiny) real example from urllib2 import urlopen import json response = urlopen('http://jsonip.com/') data = json.loads(response.read()) print data['ip'] >
72. A (tiny) real example from urllib2 import urlopen import json response = urlopen('http://jsonip.com/') data = json.loads(response.read()) print data['ip'] >
73. A (tiny) real example from urllib2 import urlopen import json response = urlopen('http://jsonip.com/') data = json.loads(response.read()) print data['ip'] 87.xxx.xxx.xxx >
74. Things you should know about virtualenv for dependency isolation pip for package management sudo apt-get install python-virtualenv mkdir mynewproject && cd mynewproject virtualenv env source env/bin/activate pip install somepackage vim mypythonfile.py python mypythonfile.py (Google them)
75. Further reading python.org Learn Python The Hard Way Python Module of the Week
76. Python on the Raspberry Pi
77. Raspberry Pi is a real computer Roughly equivalent to an Amazon EC2 Micro Instance (512MB version) Raspbian comes with Python 2.7.3 and 3.2.3 Web sites, web crawlers, social media robots, notification hubs...
78. Some useful libraries
79. Requests HTTP for Humans import requests r = requests.get('http://jsonip.com') print r.json['ip']
80. PyQuery jQuery in Python (good for scraping) from pyquery import PyQuery as pq print pq('http://brightonpy.org').find('h1').text() # prints 'Brighton and Hove Python User Group'
81. Flask A tiny web framework from flask import Flask app = Flask(__name__) @app.route("/") def hello(): return "Hello World!" app.run()
82. “Professor Cox wrote the control code in Python”
83. But you could do all this on your laptop (or on EC2)
84. “What could I do with a Raspberry Pi?”
85. “What couldn’t I do without a Raspberry Pi?”
86. Raspberry Pi is interesting because...
87. It’s small It’s cheap It’s low power
88. GPIO General Purpose Input/Output
89. Raspberry Pi <=> GPIO <=> Real world Inputs, outputs Sensors and blinky lights
90. GPIO in Python pip install rpi.gpio http://code.google.com/p/raspberry-gpio-python/ import RPi.GPIO as gpio gpio.setup(18, gpio.OUT) gpio.output(18, False)
91. Be careful “These interfaces are not plug and play and require care to avoid miswiring. The pins use a 3V3 logic level and are not tolerant of 5V levels” - RPi Wiki
92. Arduino Another tiny computer Much, much lower powered than Raspberry Pi Much better for physical computing No internet connection, can’t run Python £10-30 (several models)
93. Raspberry Pi Arduino The Real World Serial (over USB)
94. Serial Port import serial SERIALPORT = "/dev/tty.usbserial-FTDK0P3M" ser = serial.Serial(SERIALPORT, 9600) ser.write('somedata')
95. Physical Gmail Notifier http://j4mie.org/blog/how-to-make-a-physical-gmail-notifier/ WARNING: Very old article (2008). Probably crappy Python code. Required constant connection to laptop. Use RPi instead!
96. Another crazy idea
97. Another crazy idea Energy monitor without special hardware or Arduino Raspberry Pi, cheap webcam, Python
102. (or just use OCR)
103. * because everybody loves The Cloud
104. Mmm, data
105. Summary Python is easy, fun and powerful. The Raspberry Pi lets you run Python anywhere. Imagine the possibilities.TM
106. “What couldn’t I do without a Raspberry Pi?”
107. Thanks. BrightonPy @j4mie mtth.org dabapps.com brightonpy.org