Slide 1

Slide 1 text

Pythonic Dreampuf Nov. 2012

Slide 2

Slide 2 text

Agenda • Python idiom • Python tools • Python Resources

Slide 3

Slide 3 text

Python idiom There should be one, and preferably only one, obvious way to do it - from 'The Zen of Python' by Tim Peters

Slide 4

Slide 4 text

Python idiom To be Pythonic is to use the Python constructs and datastructures with clean, readable idioms. What the heck does “pythonic” mean?

Slide 5

Slide 5 text

Python idiom >>> import this

Slide 6

Slide 6 text

Python idiom Syntax & Builtin

Slide 7

Slide 7 text

Python idiom temp = foo foo = bar bar = temp (foo, bar) = (bar, foo)

Slide 8

Slide 8 text

Python idiom log_severity = None if 'severity' in configuration: log_severity = configuration['severity'] else: log_severity = log.Info log_severity = \ configuration.get('severity', log.Info)

Slide 9

Slide 9 text

Python idiom result_list = ['True', 'False', 'File not found'] result_string = '' for result in result_list: result_string += result result_list = ['True', 'False', 'File not found'] result_string = ''.join(result_list)

Slide 10

Slide 10 text

Python idiom file_handle = open(path_to_file, 'r') for line in file_handle.readlines(): if some_function_that_throws_exceptions(line): # do something file_handle.close() with open(path_to_file, 'r') as file_handle: for line in file_handle: if some_function_that_throws_exceptions(line): # do something # No need to explicitly call 'close'.

Slide 11

Slide 11 text

Python idiom if name == 'Tom' or name == 'Dick' or name == 'Harry': is_generic_name = True if name in ('Tom', 'Dick', 'Harry'): is_generic_name = True

Slide 12

Slide 12 text

Python idiom def Profile_view(request): if not check_is_logined(request): throw HTTP401 ... def Setting_view(request): if not check_is_logined(request): throw HTTP401 ... @check_is_logined_otherwise_throw def Profile_view(request): ... @check_is_logined_otherwise_throw def Setting_view(request): ...

Slide 13

Slide 13 text

Slide 14

Slide 14 text

Python idiom some_other_list = range(1, 100) my_weird_list_of_numbers = list() for element in some_other_list: if is_prime(element): my_weird_list_of_numbers.append(element+5) some_other_list = range(1, 100) my_weird_list_of_numbers = \ [element + 5 for element in some_other_list if is_prime(element)]

Slide 15

Slide 15 text

Python idiom index = 0 for element in my_container: print (index, element) index+=1 for index, element in enumerate(my_container): print (index, element)

Slide 16

Slide 16 text

Python idiom def list_gen(arg): ls = [] for i in do_some_thing(arg): ls.append(i) return ls def list_gen(arg): for i in do_some_thing(arg): yield i

Slide 17

Slide 17 text

Python idiom ls = [1,2,3,4,5,6] for i in range(len(ls)): ls[i] += 3 map(lambda x: x+3, ls)

Slide 18

Slide 18 text

Python idiom acc = 10 for i in (1,2,3): acc = acc ** i reduce(lambda x,y:x**y, [1,2,3], 10)

Slide 19

Slide 19 text

Python idiom ls = [1,2,3,4,5,6] new_ls = [] for i in range(len(ls)): if ls[i] % 2 == 0: new_ls.append(ls[i]) filter(lambda x: x % 2 == 0, ls)

Slide 20

Slide 20 text

Python idiom filter(lambda x: x % 2 == 0, ls) map(lambda x: x+3, ls) [i+3 for i in ls] [i for i in ls if i % 2 == 0]

Slide 21

Slide 21 text

Python idiom itertools

Slide 22

Slide 22 text

Itertools Iterator Arguments Results Example count() start, [step] start, start+step, start+2*step, ... count(10) --> 10 11 12 13 14 ... cycle() p p0, p1, ... plast, p0, p1, ... cycle('ABCD') --> A B C D A B C D ... repeat() elem [,n] elem, elem, elem, ... endlessly or up to n times repeat(10, 3) --> 10 10 10 chain() p, q, ... p0, p1, ... plast, q0, q1, ... chain('ABC', 'DEF') --> A B C D E F compress() data, selectors (d[0] if s[0]), (d[1] if s[1]), ... compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F dropwhile() pred, seq seq[n], seq[n+1], starting when pred fails dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1 product('ABCD', repeat=2) p, q, ... [repeat=1] AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD

Slide 23

Slide 23 text

Itertools.groupby [('"AS-IS".', ['"AS-IS".']), ('"Defect"', ['"Defect"']), ('"Pro-', ['"Pro-']), ('"Project', ['"Project']), ('"Right', ['"Right']), ('"Small', ['"Small', '"Small']), ('"small', ['"small']), ('#1787]', ['#1787]']), ("&c.'", ["&c.'"]), ("''Tis", ["''Tis"]), ("'A", ["'A", "'A", "'A", "'A", "'A"]), ... ) keywords = groupby(sorted(hamlet.split())) [('the', 970), ('and', 708), ('of', 666), ('to', 632), ('I', 521), ('a', 466), ('my', 444), ('in', 391), ('you', 383), ('Ham.', 358), ('is', 318), ('his', 284), ('it', 274), ('not', 260), ... ]

Slide 24

Slide 24 text

Python idiom collections

Slide 25

Slide 25 text

collections deque list-like container with fast appends and pops on either end >= 2.4 Counter dict subclass for counting hashable objects >= 2.7 defaultdict dict subclass that calls a factory function to supply missing values >= 2.5 OrderedDict dict subclass that remembers the order entries were added >= 2.7 namedtuple() factory function for creating tuple subclasses with named ﬁelds >= 2.6

Slide 26

Slide 26 text

collections.deque $ python -m timeit \ -s 'from collections import deque; ls = deque();' \ 'ls.appendleft(1);' 10000000 loops, best of 3: 0.126 usec per loop $ python -m timeit -s 'ls = [];' 'ls.insert(1, 0);' 100000 loops, best of 3: 41.9 usec per loop

Slide 27

Slide 27 text

collections.Counter >>> # Tally occurrences of words in a list >>> cnt = Counter() >>> for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']: ... cnt[word] += 1 >>> cnt Counter({'blue': 3, 'red': 2, 'green': 1}) >>> # Find the ten most common words in Hamlet >>> import re >>> words = re.findall('\w+', open('hamlet.txt').read().lower()) >>> Counter(words).most_common(10) [('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631), ('you', 554), ('a', 546), ('my', 514), ('hamlet', 471), ('in', 451)]

Slide 28

Slide 28 text

collections.defaultdict >>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)] >>> d = defaultdict(list) >>> for k, v in s: ... d[k].append(v) ... >>> d.items() [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

Slide 29

Slide 29 text

Python idiom unittest

Slide 30

Slide 30 text

No content

Slide 31

Slide 31 text

Unittest $ python test.py ... ---------------------------------------------------------------------- Ran 3 tests in 0.000s OK $ python test.py TestSequenceFunctions $ python test.py TestSequenceFunctions.test_choice

Slide 32

Slide 32 text

Python idiom functools

Slide 33

Slide 33 text

functools.wraps >>> from functools import wraps >>> def my_decorator(f): ... @wraps(f) ... def wrapper(*args, **kwds): ... print 'Calling decorated function' ... return f(*args, **kwds) ... return wrapper ... >>> @my_decorator ... def example(): ... """Docstring""" ... print 'Called example function' ... >>> example() Calling decorated function Called example function >>> example.__name__ 'example' >>> example.__doc__ 'Docstring'

Slide 34

Slide 34 text

functools.partial >>> from functools import partial >>> basetwo = partial(int, base=2) >>> basetwo.__doc__ = 'Convert base 2 string to an int.' >>> basetwo('10010') 18 >>> int("1001") 1001 >>> int("1001", base=2) 9

Slide 35

Slide 35 text

Python idiom contextlib

Slide 36

Slide 36 text

contextlib.contextmanager from contextlib import contextmanager @contextmanager def tag(name): print "<%s>" % name yield print "%s>" % name >>> with tag("h1"): ... print "foo" ...

foo

Slide 37

Slide 37 text

contextlib.closing from contextlib import closing import urllib with closing(urllib.urlopen('http://www.python.org')) as page: for line in page: print line from contextlib import contextmanager @contextmanager def closing(thing): try: yield thing finally: thing.close()

Slide 38

Slide 38 text

Python tools

Slide 39

Slide 39 text

Python tool virtualenv

Slide 40

Slide 40 text

Virtualenv virtualenv is a tool to create isolated Python environments.

Slide 41

Slide 41 text

Virtualenv usage $ python >>> import sys, pprint >>> pprint.pprint(sys.path) ['', '/usr/lib/python2.6', '/home/dreampuf/.local/lib/python2.6/site-packages', '/usr/lib/python2.6/dist-packages', …] $ source test-env/bin/activate (test-env)$ python >>> import sys, pprint >>> pprint.pprint(sys.path) ['', '/home/dreampuf/test-env/lib/python2.6', '/home/dreampuf/test-env/lib/python2.6/site-packages', '/usr/lib/python2.6', '/usr/lib/python2.6/dist-packages', …] (test-env)$ deactive $

Slide 42

Slide 42 text

Python tool pip

Slide 43

Slide 43 text

Pip pip is a tool for installing and managing Python packages, such as those found in the Python Package Index. It's a replacement for easy_install.

Slide 44

Slide 44 text

Pip usage $ pip install simplejson [... progress report ...] Successfully installed simplejson $ pip install --upgrade simplejson [... progress report ...] Successfully installed simplejson $ pip uninstall simplejson Uninstalling simplejson: /home/me/env/lib/python2.7/site-packages/simplejson /home/me/env/lib/python2.7/site-packages/ simplejson-2.2.1-py2.7.egg-info Proceed (y/n)? y Successfully uninstalled simplejson Install Upgrade Removing

Slide 45

Slide 45 text

Pip usage (.py)$ pip freeze GitPython==0.3.2.RC1 PyYAML==3.10 async==0.6.1 gitdb==0.5.4 ipdb==0.7 ipython==0.13.1 nose==1.2.1 pycallgraph==0.5.1 pymongo==2.3 pythoscope==0.4.3 readline==6.2.4.1 ...

Slide 46

Slide 46 text

Virtualenv + Pip $ git clone code_stat/ code_stat_clone Cloning into 'code_stat_clone'... done. $ cd code_stat_clone/ $ ls README.md conﬁg.py mongo_stat.py requirements.txt test.py $ virtualenv .py New python executable in .py/bin/python Installing setuptools............done. Installing pip...s............done. $ source .py/bin/activate (.py)$ pip install -r requirements.txt Downloading/unpacking GitPython==0.3.2.RC1 (from -r requirements.txt (line 1)) Downloading/unpacking PyYAML==3.10 (from -r requirements.txt (line 2)) Downloading/unpacking async==0.6.1 (from -r requirements.txt (line 3)) .... (.py)$

Slide 47

Slide 47 text

Python tool pyreverse

Slide 48

Slide 48 text

Pyreverse Pyreverse is a set of utilities to reverse enginering Python code. It uses a representation of a Python project in a class hierarchy which can be used to extract any information (such as generating UML diagrams or unit tests, as pyargo and py2tests)

Slide 49

Slide 49 text

Pyreverse usage $pyreverse -o png -ASmy \ -f PUB_ONLY -p cherrypy \ cherrypy/

Slide 50

Slide 50 text

Pyreverse usage

Slide 51

Slide 51 text

Pyreverse usage

Slide 52

Slide 52 text

Python tool SimpleHTTPServer

Slide 53

Slide 53 text

SimpleHTTPServer usage $ python -m SimpleHTTPServer Serving HTTP on 0.0.0.0 port 8000 ...

Slide 54

Slide 54 text

SimpleHTTPServer usage

Slide 55

Slide 55 text

SimpleHTTPServer usage NEVER USE IN PRODUCTION

Slide 56

Slide 56 text

Python tool IPython

Slide 57

Slide 57 text

IPython IPython provides a rich toolkit to help you make the most out of using Python

Slide 58

Slide 58 text

IPython • Tab completion • Exploring your objects • Magic functions • Running and Editing • Debugging • History • System shell commands

Slide 59

Slide 59 text

IPython $ ipython In [1]: dict. dict.clear dict.get dict.iteritems dict.keys dict.popitem dict.values dict.viewvalues dict.copy dict.has_key dict.iterkeys dict.mro dict.setdefault dict.viewitems dict.fromkeys dict.items dict.itervalues dict.pop dict.update dict.viewkeys In [1]: %timeit range(100) 1000000 loops, best of 3: 978 ns per loop In [2]: %timeit xrange(100) 1000000 loops, best of 3: 263 ns per loop

Slide 60

Slide 60 text

Python tool pdb

Slide 61

Slide 61 text

pdb (.py)$ python -m pdb mongo_stat.py > mongo_stat.py(4)() -> __author__ = "jackdeng@freewheel.tv, byu@freewheel.tv, xhuang@freewheel.tv" (Pdb) n > mongo_stat.py(10)() -> import re (Pdb) > mongo_stat.py(11)() -> import os (Pdb) l 6 """ 7 Code Stat 8 """ 9 10 import re 11 -> import os 12 import sys 13 import time 14 import shlex (Pdb)

Slide 62

Slide 62 text

pdb ipdb = pdb + ipython

Slide 63

Slide 63 text

pudb

Slide 64

Slide 64 text

Python tool pyﬂakes

Slide 65

Slide 65 text

Pyﬂakes

Slide 66

Slide 66 text

Python Resources

Slide 67

Slide 67 text

Python Enhancement Proposals (PEPs) num title owner 1 PEP Purpose and Guidelines Warsaw, Hylton, Goodger, Coghlan 4 Deprecation of Standard Modules von Löwis 5 Guidelines for Language Evolution Prescod 6 Bug Fix Releases Aahz, Baxter 7 Style Guide for C Code GvR 8 Style Guide for Python Code GvR, Warsaw 9 Sample Plaintext PEP Template Warsaw 10 Voting Guidelines Warsaw

Slide 68

Slide 68 text

Pydoc $ pydoc enumerate Help on class enumerate in module __builtin__: class enumerate(object) | enumerate(iterable[, start]) -> iterator for index, value of iterable | | Return an enumerate object. iterable must be another object that supports | iteration. The enumerate object yields pairs containing a count (from | start, which defaults to zero) and a value yielded by the iterable argument. | enumerate is useful for obtaining an indexed list: | (0, seq[0]), (1, seq[1]), (2, seq[2]), ...

Slide 69

Slide 69 text

Python Book • A byte of Python (“Python 简明教程”) • Python Module of the Week • Expert Python Programming • Python Cookbook • http://pythonbooks.revolunet.com

Slide 70

Slide 70 text

pythonbooks.revolunet.com

Slide 71

Slide 71 text

pythonbooks.revolunet.com

Slide 72

Slide 72 text

Pycoder’s Weekly

Slide 73

Slide 73 text

python-guide.org This opinionated guide exists to provide both novice and expert Python developers a best-practice handbook to the installation, conﬁguration, and usage of Python on a daily basis. -- Kenneth Reitz(Heroku dev)

Slide 74

Slide 74 text

Python tutor

Slide 75

Slide 75 text

Google Python Style

Slide 76

Slide 76 text

Python Resources huangxin.py 有点⼉儿欢乐

Slide 77

Slide 77 text

Q&A

Slide 78

Slide 78 text

Q&A

Slide 79

Slide 79 text

Reference(1) • - [What the heck does "pythonic" mean?](http://halitalptekin.tumblr.com/post/ 30028271874/pythonic-syntax) • - [Python Objects, types, classes, instances - a glossary](http://eli.thegreenplace.net/ 2012/03/30/python-objects-types-classes-and-instances-a-glossary/) • - [Python Application Deployment with Native Packages](http://hynek.me/articles/ python-app-deployment-with-native-packages/) • - [Writing Idiomatic Python](http://www.jeffknupp.com/blog/2012/10/04/writing- idiomatic-python/) • - [Presentation: pip and virtualenv](http://mathematism.com/2009/07/30/ presentation-pip-and-virtualenv/) • - [Welcome to The Hitchhiker’s Guide to Packaging](http://guide.python- distribute.org) • - [Index of Python Enhancement Proposals (PEPs)](http://www.python.org/dev/ peps/)

Slide 80

Slide 80 text

Reference(2) • - [PyCoder's Weekly](http://pycoders.com) • - [Google Python Style Guide](http://google-styleguide.googlecode.com/svn/trunk/ pyguide.html) • - [Python Guide](http://python-guide.org) • - [PythonBook](http://pythonbooks.revolunet.com) • - [Python Tutor](http://www.pythontutor.com)