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Python, the good parts

Miguel Araujo
November 23, 2013

Python, the good parts

Pycon Spain 2013 talk highlighting the best parts of Python and things you should know if starting in Python.

Miguel Araujo

November 23, 2013
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  1. El zen de Python - PEP20 •  Explícito es mejor

    que implícito •  Plano es mejor que anidado •  La legibilidad cuenta •  Debería haber una-- y preferiblamente solo una-- forma obvia de hacer algo.
  2. No pythonico names = ['Juan', 'Pedro', 'Isabel'] i = 0

    while (i < len(names)): print names[i] i += 1
  3. No pythonico if name == "Juan" or name == "Pedro"

    or name == "Maria": Pythonico if name in ("Juan", "Pedro", "Maria"):
  4. No pythonico numbers = [1, 2, 3, 4] total =

    0 for number in numbers: total += number Pythonico total = sum(numbers)
  5. Coding style - PEP8 Code is read much more often

    than is written Guido Van Rossum “
  6. Coding style - PEP8 •  Indentar con 4 espacios •

     Columnas de 80 ó 100 caracteres •  Separar clases y funciones de primer nivel por 2 espacios •  Imports en lineas diferentes import sys import os
  7. Coding style - Espacios •  Sí: spam(ham[1], {eggs: 2}) No:

    spam( ham[ 1 ], { eggs: 2 } ) •  Sí: x, y = 4, 5 No: x , y = 4 , 5 •  Sí: def publish(message=None) No:def publish(message = None)
  8. people = { "nombre": "Juan", "nombre": "Pedro", "nombre": "Maria" }

    people = { "nombre": "Juan", "nombre": "Pedro", "nombre": "Maria" } Coding style - indentar
  9. Expansión de listas def print_args(*args): for arg in args: print

    arg random_list = [1, "hi", [2, 3]] print_args(*random_list)
  10. Expansión de diccionarios def search_feed(num_messages, min_favs, user_handle): [...] search_feed(num_messages=20, min_favs=5,

    user_handle='maraujop') search_feed(**{ 'num_messages': 20, 'min_favs': 5, 'user_handle': 'maraujop' })
  11. Decoradores - PEP 318 from decorator import decorator @decorator def

    trace(f, *args, **kwargs): print "calling %s with args %s, %s" % (f, args, kwargs) return f(*args, **kwargs) @trace def search_feed(num_messages, min_favs, user_handle): print "Searching feed..."
  12. setattr / hasattr person = Person() variable_name = 'age' value

    = 26 setattr(person, variable_name, value) hasattr(person, variable_name) hasattr(person, 'age')
  13. Clases base abstractas import abc class Example: __metaclass__ = abc.ABCMeta

    @abc.abstractmethod def abstract_method(self): pass @abc.abstractproperty def abstract_property(self): pass
  14. Métodos magicos class Agenda: def __init__(self, description): self.people = [

    ] self.description = description def __getattr__(self, name): return object.__getattribute__(self.people, name) office = Agenda('People in the office') office.append({'name': 'Miguel', 'age': 26}) print office.description print [person['age'] for person in office]
  15. Métodos magicos class Agenda: def __len__(self): return len(self.people) def __contains__(self,

    item): return item.lower() in [person['name'].lower() for person in self.people] print len(office) for name in ('Miguel', 'Juan'): if name in office: print "%s in office" % name
  16. Iterando varias colecciones names = ["Juan", "Pedro", "Isabel", "Maria"] numbers

    = [23, 31, 18] for name, number in zip(names, numbers): print "name %s number %s" % (name, number) [('Juan', 23), ('Pedro', 31), ('Isabel', 18)]
  17. Crear diccionarios names = ["Miguel", "Juan", "Pedro"] ages = [21,

    22, 34] zip(names, ages) [('Miguel', 21), ('Juan', 22), ('Pedro', 34)] dict(zip(names, ages)) {'Juan': 22, 'Miguel': 21, 'Pedro': 34}
  18. Contar con diccionarios from collections import defaultdict message = "Bienvenidos

    a la primera PyCon España, la primera" count = defaultdict(int) for word in message.split(): count[word] += 1
  19. Contar con Counter from collections import Counter message = "Bienvenidos

    a la primera PyCon España, la primera" count = Counter(message.split())
  20. Funcional •  Ideal para trabajar estructuras de datos •  No

    debe abusarse de ella, ni obsesionarse con ella
  21. Ordenar lista de diccionarios people = [ {'edad': 14, 'nombre':

    'Juan'}, {'edad': 26, 'nombre': 'Miguel'}, {'edad': 30, 'nombre': 'Aria'} ] sorted(people, key=lambda person: person['edad'])
  22. Ordenar lista de diccionarios •  Las lambdas son lentas, itemgetter

    está implementado en C •  Para muchos más fácil de leer y más corto from operator import itemgetter sorted(people, key=itemgetter('edad'))
  23. List comprehensions - PEP 202 •  Las llamadas a función

    son cacheadas, son rápidas words = ["hola", "que", "tal"] [word.upper() for word in words]
  24. filter people = [ {'edad': 24, 'nombre': 'Saul'}, {'edad': 22,

    'nombre': 'Juan'} ] filter(lambda person: person['edad'] > 22, people) [{'edad': 24, 'nombre': 'Saul'}]
  25. Aplanando estructuras de datos from itertools import chain list(chain.from_iterable([ [{"nombre":

    "Jorge"}, {"nombre": "Pedro"}], [{"nombre": "Jesus"}] ])) [{'nombre': 'Jorge'}, {'nombre': 'Pedro'}, {'nombre': 'Jesus'}]
  26. Python rocks •  Un ecosistema robusto, maduro y de calidad

    •  Tests y documentación •  Entornos virtuales y pip
  27. Python requests •  rauth OAuth 1.0/a, 2.0, y Ofly •

     HTTPretty Mockear urls y sus respuestas •  httpie un cURL para humanos •  Muchos bindings para APIs
  28. pytz from datetime import datetime import pytz now = datetime.utcnow()

    datetime.datetime(2013, 11, 17, 14, 13, 51, 641900) now = now.replace(tzinfo=pytz.utc) datetime.datetime(2013, 11, 17, 14, 13, 51, 641900, tzinfo=<UTC>) now.astimezone(pytz.timezone("Europe/Madrid")) datetime.datetime(2013, 11, 17, 15, 13, 51, 641900, tzinfo=<DstTzInfo 'Europe/Madrid' CET+1:00:00 STD>)
  29. python-dateutil import calendar from dateutil.relativedelta import relativedelta now + relativedelta(month=1,

    day=23) now + relativedelta(months=-1, days=5) now + relativedelta(weekday=calendar.FRIDAY)
  30. ORMs •  SQLAlchemy El ORM más potente de Python y

    mucho más •  peewee Similar al ORM de Django's pero con un API más consistente •  Django ORM
  31. Más •  Pandas Librería de análisis de datos •  pattern

    Data mining •  Boto Interfaz para AWS •  Pillow Librería para manejo de imágenes •  Path Manejo de rutas y ficheros •  Docopt Parser de línea de comandos •  bleach Sanitizador de HTML •  Jinja Motor de plantillas
  32. Ejemplo nltk Natural Language Tool Kit tokens = nltk.word_tokenize("I like

    eating chocolate with milk") tagged = nltk.pos_tag(tokens) [(u'I', u'PRP'), (u'like', u'VB'), (u'eating', u'VBG'), (u'chocolate', u'NN'), (u'with', u'IN'), (u'milk', u'NN')]
  33. Ejemplo TextBlob API sencilla para procesar datos textuales blob =

    TextBlob("I like eating chocolate with milk") blob.tags [(u'I', u'PRP'), (u'like', u'VB'), (u'eating', u'VBG'), (u'chocolate', u'NN'), (u'with', u'IN'), (u'milk', u'NN')]
  34. Ejemplo OpenCV import cv2 import cv2.cv as cv def camshift_tracking(img1,

    img2, bb): hsv = cv2.cvtColor(img1, cv.CV_BGR2HSV) mask = cv2.inRange(hsv, np.array((0., 60., 32.)), np.array((180., 255., 255.))) x0, y0, w, h = bb x1 = x0 + w -1 y1 = y0 + h -1 hsv_roi = hsv[y0:y1, x0:x1] mask_roi = mask[y0:y1, x0:x1] hist = cv2.calcHist( [hsv_roi], [0], mask_roi, [16], [0, 180] ) cv2.normalize(hist, hist, 0, 255, cv2.NORM_MINMAX); hist_flat = hist.reshape(-1) prob = cv2.calcBackProject([hsv,cv2.cvtColor(img2, cv.CV_BGR2HSV)], [0], hist_flat, [0, 180], 1) prob &= mask term_crit = ( cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 1 ) new_ellipse, track_window = cv2.CamShift(prob, bb, term_crit) return track_window
  35. Ejemplo SimpleCV camera, display = Camera(), Display() bounding_box = (100,

    200, 100, 100) track_set = [ ] previous = camera.getImage() while display.isNotDone(): frame = camera.getImage() track_set = frame.track('camshift', track_set, previous, bounding_box) track_set.drawBB() previous = frame frame.save(display)
  36. Ejemplo urllib2 import urllib2 gh_url = 'https://api.github.com' req = urllib2.Request(gh_url)

    password_manager = urllib2.HTTPPasswordMgrWithDefaultRealm() password_manager.add_password(None, gh_url, 'user', 'pass') auth_manager = urllib2.HTTPBasicAuthHandler(password_manager) opener = urllib2.build_opener(auth_manager) urllib2.install_opener(opener) handler = urllib2.urlopen(req) print handler.getcode() print handler.headers.getheader('content-type')
  37. Ejemplo argparse - PEP 389 if __name__ == '__main__': parser

    = argparse.ArgumentParser() parser.add_argument('--run', dest='action', help='argparse example') args = parser.parse_args() if args.action == 'update': print "Updating..." elif args.action == 'watch': print "Watch..."
  38. """ Usage: example.py run (update|watch) example.py -h | --help example.py

    --version Options: -h --help Show help message. --version Show version. """ Ejemplo docopt if __name__ == '__main__': args = docopt(__doc__, version='1.0') if args['update']: print "Updating..." elif args['watch']: print "Watch..."
  39. Python moderno •  Python 2.0 en el año 2000 •

     PEPs •  Recolector de basura / soporte de Unicode •  PEP 1 -- PEP Purpose and Guidelines