Python utan-stodhjul-motorsag

Utan stödhjul och
motorsåg

Vad är Python?

● Ett dynamiskt typat språk
● Designat för enkelhet och tydlighet

It is the only language co-designed for the
most advanced and the complete novice.

[David Goodger]

Plattformar

● Python = CPython
● Jython (JVM)

● IronPython (.NET, Mono)

● PyPy (Python in Python)

Användningsområden

admin, byggen och driftsättning

webbapps, webbtjänster/+klienter

verktygsklister & GUIn (vanligt på linux)

dataskyffling/-konvertering/-analys

Scripta verktyg

Grafik (Gimp, Inkscape, Blender, ...),
LibreOffice, ...

Spel (Battlefield 2+, Civ IV, EVE-Online, ...)

DVCS: Mercurial, Bazaar...

.. Sun, Microsoft, Canonical, O'Reilly, Lucasfilm,
Nasa, Sourceforge, ...

Årets språk enligt Tiobe

Bästa tillväxten

2007
2010

Moget

Utveckling & drift: doctest, nosetests, distribute,
pip, virtualenv, ...

Paket för allt: data, sysadmin, webb, grafik,
matematik, parallellism...

Vad är viktigt?

Läsbarhet!

Namngivning!

Programming The
Way Guido Indented It

def to_roman(num):

assert num > 0 and num < 4000

result = []

for d, r in NUMERALS:

while num >= d:
result.append(r)
num -= d

return ''.join(result)

"In soviet russia, braces scope you"

from __future__ import braces

...
SyntaxError: not a chance

Effektivt

tokens = ['a', 'b', 'c', 'B', 'dd', 'C', 'DD']

similar = {}

for token in tokens:
key = token.lower()
similar.setdefault(key, []).append(token)

Lättanvänt

for key, tokens in similar.items():

if len(tokens) > 1:
print("Similar (like %s):" % key)

for token in tokens:
print(token)

Generella behållare

● list() == []
● dict() == {}

● tuple() == ()

● set()

Python är interaktivt

$ python
Python 2.7.1 [...]
Type "help", "copyright", "credits" or "license" for
more information.
>>>

>>> def add(a, b=1):
... return a + b
...
>>> add(1)
2
>>> add(1, 2)
3
>>> add(2, b=3)
5
>>> add(b=3, a=2)
5

"""
Usage:

>>> usr = Path('/usr')
>>> bin = usr.segment('local').segment('bin')
>>> str(bin)
'/usr/local/bin'
"""

class Path:
def __init__(self, base):
self.base = base

def segment(self, name):
return Path(self.base + '/' + name)

def __str__(self):
return self.base

__protokoll__

Betyder används under ytan

Tydliga sammanhang

Börjar bukta när en dålig idé växer

● state är explicit (self)

"""
Usage:

>>> usr = Path('/usr')
>>> bin = usr.segment('local').segment('bin')
>>> str(bin)
'/usr/local/bin'
"""

class Path(str):
def segment(self, name):
return Path(self + '/' + name)

Allt är objekt

● primitiver
● collections

● funktioner, klasser

● moduler, paket

"""Usage:
Closures
>>> mkpasswd = salter("@secret#salt")
>>> mkpasswd("qwerty")
'4ef6056fb6f424f2e848705fd5e40602'
"""

from hashlib import md5

def salter(salt):

def salted_encrypt(value):
return md5(salt + value).hexdigest()

return salted_encrypt

Funktionell @dekoration

from django.views.decorators.cache import cache_page

@cache_page(15 * 60)
def slashdot_index(request):
result = resource_intensive_operation(request)
return view_for(result)

Reduce boilerplate..

try:
f = open('file1.txt')
for line in f:
print(line)

finally:
f.close()

.. with contexts

with open('file1.txt') as f:

for line in f:
print(line)

Generators

def public_files(dirname):
for fname in os.listdir(dirname):
if not fname.startswith('.'):
yield fname

for fname in public_files('.'):
open(fname)

Maskinellt procedurell

publicfiles = []

for fname in os.listdir('.'):

if not fname.startswith('.'):
publicfiles.append(open(fname))

Tillståndslös spaghetti

publicfiles = map(lambda fname: open(fname),
filter(lambda fname:
not fname.startswith('.'),
os.listdir('.')))

List comprehensions

publicfiles = [open(fname)
for fname in os.listdir('.')
if not fname.startswith('.')]

Generator comprehensions

publicfiles = (open(fname)
for fname in os.listdir('.')
if not fname.startswith('.'))

process(open(fname) for fname in os.listdir('.')
if not fname.startswith('.'))

There should be one — and
preferably only one — obvious
way to do it.

Although that way may not be
obvious at first unless you're
Dutch.

Python ger dig

● Enkel men kraftfull kod
● Fokus på lösningen

Image Tributes (CC)
Python, Google, YouTube, Spotify logos & Amazon Python Day Poster photo courtesy of
respective organization.

Night train

"And so thy path shall be a track of light"

"Documents Reveal Django Pony, Caught In Tail Of Lies." / _why

"inch by inch"

"Wasserglas"

"I am Jack, hear me lumber!"

"Bend me, Shape me, any way you want me."

Python utan-stodhjul-motorsag

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