Learning Python from Data

LEARNING PYTHON FROM DATA Mosky 1

THIS SLIDE • The online version is at https://speakerdeck.com/mosky/learning-python-from-data. • The examples are at https://github.com/moskytw/learning-python-from-data-examples. 2

MOSKY • I am working at Pinkoi. 3

MOSKY • I am working at Pinkoi. • I've taught Python for 100+ hours. 3

MOSKY • I am working at Pinkoi. • I've taught Python for 100+ hours. • A speaker at COSCUP 2014, PyCon SG 2014, PyCon APAC 014, OSDC 2014, PyCon APAC 2013, COSCUP 2014, ... 3

MOSKY • I am working at Pinkoi. • I've taught Python for 100+ hours. • A speaker at COSCUP 2014, PyCon SG 2014, PyCon APAC 014, OSDC 2014, PyCon APAC 2013, COSCUP 2014, ... • The author of the Python packages: MoSQL, Clime, ZIPCodeTW, ... 3

MOSKY • I am working at Pinkoi. • I've taught Python for 100+ hours. • A speaker at COSCUP 2014, PyCon SG 2014, PyCon APAC 014, OSDC 2014, PyCon APAC 2013, COSCUP 2014, ... • The author of the Python packages: MoSQL, Clime, ZIPCodeTW, ... • http://mosky.tw/ 3

SCHEDULE •Warm-up • Packages - Install the packages we need. 4

SCHEDULE •Warm-up • Packages - Install the packages we need. • CSV - Download a CSV from the Internet and handle it. 4

SCHEDULE •Warm-up • Packages - Install the packages we need. • CSV - Download a CSV from the Internet and handle it. • HTML - Parse a HTML source code and write a Web crawler. 4

SCHEDULE •Warm-up • Packages - Install the packages we need. • CSV - Download a CSV from the Internet and handle it. • HTML - Parse a HTML source code and write a Web crawler. • SQL - Save data into a SQLite database. 4

SCHEDULE •Warm-up • Packages - Install the packages we need. • CSV - Download a CSV from the Internet and handle it. • HTML - Parse a HTML source code and write a Web crawler. • SQL - Save data into a SQLite database. • The End 4

2 OR 3? • Use Python 3! • But it actually depends on the libs you need. 7

2 OR 3? • Use Python 3! • But it actually depends on the libs you need. • https://python3wos.appspot.com/ 7

2 OR 3? • Use Python 3! • But it actually depends on the libs you need. • https://python3wos.appspot.com/ •We will go ahead with Python 2.7, but I will also introduce the changes in Python 3. 7

THE ONLINE RESOURCES • The Python Official Doc • http://docs.python.org • The Python Tutorial • The Python Standard Library 8

THE ONLINE RESOURCES • The Python Official Doc • http://docs.python.org • The Python Tutorial • The Python Standard Library • My Past Slides • Programming with Python - Basic • Programming with Python - Adv. 8

THE BOOKS • Learning Python by Mark Lutz 9

THE BOOKS • Learning Python by Mark Lutz • Programming in Python 3 by Mark Summerfield 9

THE BOOKS • Learning Python by Mark Lutz • Programming in Python 3 by Mark Summerfield • Python Essential Reference by David Beazley 9

PREPARATION • Did you say "hello" to Python? 10

PREPARATION • Did you say "hello" to Python? • If no, visit • http://www.slideshare.net/moskytw/programming-with-python- basic. 10

PREPARATION • Did you say "hello" to Python? • If no, visit • http://www.slideshare.net/moskytw/programming-with-python- basic. • If yes, open your Python shell. 10

WARM-UP The things you must know. 11

MATH & VARS 2 + 3 2 - 3 2 * 3 2 / 3, -2 / 3 ! (1+10)*10 / 2 ! 2.0 / 3 ! 2 % 3 ! 2 ** 3 x = 2 ! y = 3 ! z = x + y ! print z ! '#' * 10 12

FOR for i in [0, 1, 2, 3, 4]: print i ! items = [0, 1, 2, 3, 4] for i in items: print i ! for i in range(5): print i ! ! ! chars = 'SAHFI' for i, c in enumerate(chars): print i, c ! ! words = ('Samsung', 'Apple', 'HP', 'Foxconn', 'IBM') for c, w in zip(chars, words): print c, w 13

IF for i in range(1, 10): if i % 2 == 0: print '{} is divisible by 2'.format(i) elif i % 3 == 0: print '{} is divisible by 3'.format(i) else: print '{} is not divisible by 2 nor 3'.format(i) 14

WHILE while 1: n = int(raw_input('How big pyramid do you want? ')) if n <= 0: print 'It must greater than 0: {}'.format(n) continue break 15

TRY while 1: ! try: n = int(raw_input('How big pyramid do you want? ')) except ValueError as e: print 'It must be a number: {}'.format(e) continue ! if n <= 0: print 'It must greater than 0: {}'.format(n) continue ! break 16

LOOP ... ELSE for n in range(2, 100): for i in range(2, n): if n % i == 0: break else: print '{} is a prime!'.format(n) 17

A PYRAMID * *** ***** ******* ********* *********** ************* *************** ***************** ******************* 18

A FATER PYRAMID * ***** ********* ************* ******************* 19

LIST COMPREHENSION [ n for n in range(2, 100) if not any(n % i == 0 for i in range(2, n)) ] 21

PACKAGES import is important. 22

GET PIP - UN*X • Debian family • # apt-get install python-pip 24

GET PIP - UN*X • Debian family • # apt-get install python-pip • Rehat family • # yum install python-pip 24

GET PIP - UN*X • Debian family • # apt-get install python-pip • Rehat family • # yum install python-pip • Mac OS X • # easy_install pip 24

GET PIP - WIN * • Follow the steps in http://stackoverflow.com/questions/ 4750806/how-to-install-pip-on-windows. 25

GET PIP - WIN * • Follow the steps in http://stackoverflow.com/questions/ 4750806/how-to-install-pip-on-windows. • Or just use easy_install to install. The easy_install should be found at C:Python27Scripts. 25

GET PIP - WIN * • Follow the steps in http://stackoverflow.com/questions/ 4750806/how-to-install-pip-on-windows. • Or just use easy_install to install. The easy_install should be found at C:Python27Scripts. • Or find the Windows installer on Python Package Index. 25

3-RD PARTY PACKAGES • requests - Python HTTP for Humans 26

3-RD PARTY PACKAGES • requests - Python HTTP for Humans • lxml - Pythonic XML processing library 26

3-RD PARTY PACKAGES • requests - Python HTTP for Humans • lxml - Pythonic XML processing library • uniout - Print the object representation in readable chars. 26

3-RD PARTY PACKAGES • requests - Python HTTP for Humans • lxml - Pythonic XML processing library • uniout - Print the object representation in readable chars. • clime - Convert module into a CLI program w/o any config. 26

CSV Let's start from making a HTTP request! 28

HTTP GET import requests ! #url = 'http://stats.moe.gov.tw/files/school/101/ u1_new.csv' url = 'https://raw.github.com/moskytw/learning-python- from-data-examples/master/sql/schools.csv' ! print requests.get(url).content ! #print requests.get(url).text 29

FILE save_path = 'school_list.csv' ! with open(save_path, 'w') as f: f.write(requests.get(url).content) ! with open(save_path) as f: print f.read() ! with open(save_path) as f: for line in f: print line, 30

DEF from os.path import basename ! def save(url, path=None): ! if not path: path = basename(url) ! with open(path, 'w') as f: f.write(requests.get(url).content) 31

CSV import csv from os.path import exists ! if not exists(save_path): save(url, save_path) ! with open(save_path) as f: for row in csv.reader(f): print row 32

+ UNIOUT import csv from os.path import exists import uniout # You want this! ! if not exists(save_path): save(url, save_path) ! with open(save_path) as f: for row in csv.reader(f): print row 33

NEXT with open(save_path) as f: next(f) # skip the unwanted lines next(f) for row in csv.reader(f): print row 34

DICT READER with open(save_path) as f: next(f) next(f) for row in csv.DictReader(f): print row ! # We now have a great output. :) 35

DEF AGAIN def parse_to_school_list(path): school_list = [] with open(path) as f: next(f) next(f) for school in csv.DictReader(f): school_list.append(school) ! return school_list[:-2] 36

+ COMPREHENSION def parse_to_school_list(path='schools.csv'): with open(path) as f: next(f) next(f) school_list = [school for school in csv.DictReader(f)][:-2] ! return school_list 37

+ PRETTY PRINT from pprint import pprint ! pprint(parse_to_school_list(save_path)) ! # AWESOME! 38

PYTHONIC school_list = parse_to_school_list(save_path) ! # hmmm ... ! for school in shcool_list: print shcool['School Name'] ! # It is more Pythonic! :) ! print [school['School Name'] for school in school_list] 39

GROUP BY from itertools import groupby ! # You MUST sort it. keyfunc = lambda school: school['County'] school_list.sort(key=keyfunc) ! for county, schools in groupby(school_list, keyfunc): for school in schools: print '%s %r' % (county, school) print '---' 40

DOCSTRING '''It contains some useful function for paring data from government.''' ! def save(url, path=None): '''It saves data from `url` to `path`.''' ... ! --- Shell --- ! $ pydoc csv_docstring 41

CLIME if __name__ == '__main__': import clime.now ! --- shell --- ! $ python csv_clime.py usage: basename <p> or: parse-to-school-list <path> or: save [--path] <url> ! It contains some userful function for parsing data from government. 42

DOC TIPS help(requests) ! print dir(requests) ! print 'n'.join(dir(requests)) 43

HTML Have fun with the final crawler. ;) 45

LXML import requests from lxml import etree ! content = requests.get('http://clbc.tw').content root = etree.HTML(content) ! print root 46

CACHE from os.path import exists ! cache_path = 'cache.html' ! if exists(cache_path): with open(cache_path) as f: content = f.read() else: content = requests.get('http://clbc.tw').content with open(cache_path, 'w') as f: f.write(content) 47

SEARCHING head = root.find('head') print head ! head_children = head.getchildren() print head_children ! metas = head.findall('meta') print metas ! title_text = head.findtext('title') print title_text 48

XPATH titles = root.xpath('/html/head/title') print titles[0].text ! title_texts = root.xpath('/html/head/title/text()') print title_texts[0] ! as_ = root.xpath('//a') print as_ print [a.get('href') for a in as_] 49

MD5 from hashlib import md5 ! message = 'There should be one-- and preferably only one --obvious way to do it.' ! print md5(message).hexdigest() ! # Actually, it is noting about HTML. 50

DEF GET from os import makedirs from os.path import exists, join ! def get(url, cache_dir_path='cache/'): ! if not exists(cache_dir_path): makedirs(cache_dir) ! cache_path = join(cache_dir_path, md5(url).hexdigest()) ! ... 51

DEF FIND_URLS def find_urls(content): root = etree.HTML(content) return [ a.attrib['href'] for a in root.xpath('//a') if 'href' in a.attrib ] 52

BFS 1/2 NEW = 0 QUEUED = 1 VISITED = 2 ! def search_urls(url): ! url_queue = [url] url_state_map = {url: QUEUED} ! while url_queue: ! url = url_queue.pop(0) print url 53

BFS 2/2 # continue the previous page try: found_urls = find_urls(get(url)) except Exception, e: url_state_map[url] = e print 'Exception: %s' % e except KeyboardInterrupt, e: return url_state_map else: for found_url in found_urls: if not url_state_map.get(found_url, NEW): url_queue.append(found_url) url_state_map[found_url] = QUEUED url_state_map[url] = VISITED 54

DEQUE from collections import deque ... ! def search_urls(url): url_queue = deque([url]) ... while url_queue: ! url = url_queue.popleft() print url ... 55

YIELD ... ! def search_urls(url): ... while url_queue: ! url = url_queue.pop(0) yield url ... except KeyboardInterrupt, e: print url_state_map return ... 56

SQL How about saving the CSV file into a db? 58

TABLE CREATE TABLE schools ( id TEXT PRIMARY KEY, name TEXT, county TEXT, address TEXT, phone TEXT, url TEXT, type TEXT ); ! DROP TABLE schools; 59

CRUD INSERT INTO schools (id, name) VALUES ('1', 'The First'); INSERT INTO schools VALUES (...); ! SELECT * FROM schools WHERE id='1'; SELECT name FROM schools WHERE id='1'; ! UPDATE schools SET id='10' WHERE id='1'; ! DELETE FROM schools WHERE id='10'; 60

COMMON PATTERN import sqlite3 ! db_path = 'schools.db' conn = sqlite3.connect(db_path) cur = conn.cursor() ! cur.execute('''CREATE TABLE schools ( ... )''') conn.commit() ! cur.close() conn.close() 61

ROLLBACK ... ! try: cur.execute('...') except: conn.rollback() raise else: conn.commit() ! ... 62

PARAMETERIZE QUERY ... ! rows = ... ! for row in rows: cur.execute('INSERT INTO schools VALUES (?, ?, ?, ?, ?, ?, ?)', row) ! conn.commit() ! ... 63

EXECUTEMANY ... ! rows = ... ! cur.executemany('INSERT INTO schools VALUES (?, ?, ?, ?, ?, ?, ?)', rows) ! conn.commit() ! ... 64

FETCH ... cur.execute('select * from schools') ! print cur.fetchone() ! # or print cur.fetchall() ! # or for row in cur: print row ... 65

TEXT FACTORY # SQLite only: Let you pass the 8-bit string as parameter. ! ... ! conn = sqlite3.connect(db_path) conn.text_factory = str ! ... 66

ROW FACTORY # SQLite only: Let you convert tuple into dict. It is `DictCursor` in some other connectors. ! def dict_factory(cursor, row): d = {} for idx, col in enumerate(cursor.description): d[col[0]] = row[idx] return d ! ... con.row_factory = dict_factory ... 67

MORE • Python DB API 2.0 • MySQLdb - MySQL connector for Python 68

MORE • Python DB API 2.0 • MySQLdb - MySQL connector for Python • Psycopg2 - PostgreSQL adapter for Python 68

MORE • Python DB API 2.0 • MySQLdb - MySQL connector for Python • Psycopg2 - PostgreSQL adapter for Python • SQLAlchemy - the Python SQL toolkit and ORM 68

MORE • Python DB API 2.0 • MySQLdb - MySQL connector for Python • Psycopg2 - PostgreSQL adapter for Python • SQLAlchemy - the Python SQL toolkit and ORM • MoSQL - Build SQL from common Python data structure. 68

THE END • You learned how to ... 69

THE END • You learned how to ... • make a HTTP request 69

THE END • You learned how to ... • make a HTTP request • load a CSV file 69

THE END • You learned how to ... • make a HTTP request • load a CSV file • parse a HTML file 69

THE END • You learned how to ... • make a HTTP request • load a CSV file • parse a HTML file • write a Web crawler 69

THE END • You learned how to ... • make a HTTP request • load a CSV file • parse a HTML file • write a Web crawler • use SQL with SQLite 69

THE END • You learned how to ... • make a HTTP request • load a CSV file • parse a HTML file • write a Web crawler • use SQL with SQLite • and lot of techniques today. ;) 69

Learning Python from Data

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