Quickies

[categories] [index] [all (527)] [latest]

Python
  1. A simple class to get quickly started
    #!/usr/bin/python
    # -*- coding: iso-8859-1 -*-
    __version__ = "$Revision: 0.1 $"
    __author__ = "Nicolas Seriot"
    __date__ = "2005-03-27"

    class Car:
        """
        This class represents a Car
        """
            
        # constructor
        def __init__(self, brand, color):        
            self.brand = brand
            self.color = color
            
        # a method
        def paint(self, color):
            self.color = color
        
        # string description
        def __str__(self):
            return self.brand + ", " + self.color
        
        # destructor
        def __del__(self):
            pass
            
    if __name__ == "__main__":
        
        c1 = Car("Ford", "blue")
        c2 = Car("Ferrari", "red")
        
        cars = [c1, c2]
        
        c2.paint("pink")
        
        for c in cars:
            print c
    $ python cars.py
Ford, blue
Ferrari, pink
  2. Build a dictionary with keys and values
    keys = ['a', 'b', 'c']
values = [1, 2, 3]
d = dict(zip(keys, values))

    {'a': 1, 'c': 3, 'b': 2}

  3. Build a dictionary with list comprehension
    >>> dict((k, []) for k in ['a', 'b', 'c'])
{'a': [], 'c': [], 'b': []}
  4. Calendar arithmetics
    >>> import datetime

>>> today = datetime.date.today()
>>> today.replace(day=1)
datetime.date(2007, 2, 1)
>>> today.replace(month=today.month+1).replace(day=1)
datetime.date(2007, 3, 1)
  5. Call a function from its name
    import my_module
f = getattr(my_module, 'my_function')
result = f()

    or

    globals()["my_function"]()

    or

    locals()["my_function"]()
  6. Class methods
    class C:

    def foo(cls, y):
        print "classmethod", cls, y
    foo = classmethod(foo)

C.foo(1)
c = C()
c.foo(1)

    Unifying types and classes in Python 2.2

  7. Code coverage

    http://garethrees.org/2001/12/04/python-coverage/

    Here with a Django project:

    $ coverage.py -x manage.py test
$ coverage.py -a app/models.py
$ mate app/models.py,cover
  8. Code profiling - Python 2

    Let the profiler execute the code

    import hotshot

prof = hotshot.Profile("hotshot_stats.prof")
prof.runcall(my_function)
prof.close()

    Display results

    from hotshot import stats

s = stats.load("hotshot_stats.prof")
s.strip_dirs()
s.sort_stats('time', 'calls')
s.print_stats(20)
  9. Code profiling - Python 3
    import cProfile, pstats, io
from pstats import SortKey

# ...

pr = cProfile.Profile()
pr.enable()

f() # <- code to profile here

pr.disable()
s = io.StringIO()
sortby = SortKey.CUMULATIVE
ps = pstats.Stats(pr, stream=s).sort_stats(sortby)
ps.print_stats()
print(s.getvalue())
  10. Convert datetime to unix timestamp
    >>> import datetime
>>> import time
>>> dt = datetime.datetime(2010, 2, 25, 23, 23)
>>> time.mktime(dt.timetuple())

    1267136580.0

  11. Convert utf-8 string into latin-1
    s_latin1 = unicode(s_utf8, 'utf-8').encode('latin-1', 'replace')
  12. Count lines efficiently
    sum(1 for line in open('myfile.txt'))
  13. Create datetime from unix timestamp
    >>> import datetime
>>> datetime.datetime.fromtimestamp(1294236000)

    datetime.datetime(2011, 1, 5, 15, 0)

  14. Creation or modification dates of a file
    import os
import datetime

created_t = os.path.getctime("/etc/passwd")
modified_t = os.path.getmtime("/etc/passwd")

print datetime.datetime.fromtimestamp(created_t)
print datetime.datetime.fromtimestamp(modified_t)

    2012-07-03 12:30:39 2012-07-03 12:30:39

  15. Detach a new thread
    #!/usr/bin/python

import thread
import time

def my_function():
    while 1:
        print "thread 2"
        time.sleep(0.6)

print "-- will detach new thread"
thread.start_new_thread(my_function, ())
print "-- did detach new thread"

while 1:
    print "thread 1"
    time.sleep(1)
  16. Display date and time
    import locale
import datetime

locale.setlocale(locale.LC_ALL, 'fr_FR')
now = datetime.datetime.now()
now.strftime("%A %d %B %Y, %H:%M")
#'Samedi 20 janvier 2007, 15:17'

    Another way:

    from time import strftime
strftime("%Y-%m-%d %H:%M:%S")
#'2008-09-28 20:33:09'
  17. Display site-packages path
    $ python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()"

    /Library/Python/2.5/site-packages

  18. Enter debugger at a certain point
    import pdb
pdb.set_trace()
  19. Enumeration index

    Instead of writing:

    index = 0
for element in my_list:
    print (index, element)
    index += 1

    use:

    for index, element in enumerate(my_list):
    print (index, element)
  20. Exceptions
    class MyException(Exception):
    def __init__(self, value):
        self.value = value

    def __str__(self):
        return repr(self.value)

def myFunction():
    raise MyException("myValue")

def handleException():
    try:
        myFunction()
    except MyException as e:
        print("-- exception: %s" % e)

handleException();
  21. Filter the methods of an object according to their name
    import inspect

    from inside the object

    test_methods = inspect.getmembers(self, lambda f:inspect.ismethod(f) and f.__name__.startswith('test_'))

for (f_name, f) in test_methods:
    f()
  22. Flatten a list of lists
    >>> matrix = [[1,2,3], [4,5,6]]
>>> [x for row in matrix for x in row]
[1, 2, 3, 4, 5, 6]

    or

    >>> sum(matrix, [])
[1, 2, 3, 4, 5, 6]
  23. for loop else

    write:

    for x in data:
    if meets_condition(x):
        break
else:
    # raise error or do additional processing

    instead of:

    condition_is_met = False
for x in data:
    if meets_condition(x):
        condition_is_met = True

if not condition_is_met:
    # raise error or do additional processing

    http://shahriar.svbtle.com/pythons-else-clause-in-loops

  24. Generate a list of random numbers
    import random
random.sample(xrange(100), 3)

    [32, 49, 0]

  25. Get a random integer
    from random import randint
randint(0, 2)

    0, 1 or 2

  26. Get endianness
    import sys

if sys.byteorder == "little":
    print "little-endian platform (intel, alpha)"
else:
    print "big-endian platform (motorola, sparc)"
  27. Get environment variables
    import os

for param in os.environ.keys():
    print "%20s %s" % (param, os.environ[param])
  28. Get function source code
    import inspect

def f():
    a = 1 + 2
    return a

s = inspect.getsource(f)
print s

"""    
def f():
    a = 1 + 2
    return a
"""

lines, start = inspect.getsourcelines(f)
print lines

"""
['def f():n', '    a = 1 + 2n', '    return an']
"""
  29. Get self IP address
    import socket

print socket.gethostbyname(socket.gethostname())

    192.168.0.231

  30. Get the name of a function
    print f.__name__
  31. Get the URL out of a Mac OS X .webloc file
    def webloc_url(path):
    f = open(path)
    s = f.read()
    f.close()

    data = NSData.dataWithContentsOfFile_(path)
    plist = NSPropertyListSerialization.propertyListWithData_options_format_error_(data, 0, None, None)

    return plist[0]['URL']
  32. Handle URL loading timeout
    #!/usr/bin/python

import socket
from urllib import urlopen

socket.setdefaulttimeout(2) # secondes

try:
    print urlopen("http://checkip.dyndns.org").readlines()
except IOError:
    print "timeout"
  33. HTTP Request with Python sockets
    import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("www.seriot.ch", 80))

s.send("GET /index.php HTTP/1.1\nHost: seriot.ch\n\n")
response = s.recv(1024)
print response
  34. HTTP server
    from os import curdir, sep
from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer

class MyHandler(BaseHTTPRequestHandler):

    def do_GET(self):
        try:
            if self.path.endswith(".test"):
                self.send_response(200)
                self.send_header('Content-type',    'text/html')
                self.end_headers()
                #f = open(curdir + sep + self.path)
                #self.wfile.write(f.read())
                #f.close()
                self.wfile.write("it works")
                return
        except IOError:
            pass

        self.send_error(404,'File Not Found: %s' % self.path)

def main():
    try:
        server = HTTPServer(('', 10000), MyHandler)
        print 'started HTTPServer...'
        server.serve_forever()
    except KeyboardInterrupt:
        print '^C received, shutting down server'
        server.socket.close()

if __name__ == '__main__':
    main()
  35. httplib
    #!/usr/bin/python

import httplib

def headers_and_contents(host, path, headers):

    conn = httplib.HTTPConnection(host)
    conn.request("GET", path, None, headers)
    r = conn.getresponse()

    if r.status != 200:
        print r.status, r.reason

    h = r.getheaders()
    s = r.read()

    conn.close()

    return (h, s)

headers = {"Cookie" : "key=value;"}

(h, s) = headers_and_contents("www.apple.com", "/index.html", headers)
  36. Kill current process
    #!/usr/bin/python

import os

print "-- will kill"
pid = os.getpid()
print "-- pid:", pid
os.kill(pid, 1)
print "-- did kill"
  37. Launch an external process and get the result
    import popen2
(stdout, stdin, stderr) = popen2.popen3("ping -q -c2 www.google.com")
print stdout.readlines()
  38. Load an Cocoa Framework with PyObjC
    import objc

objc.loadBundle("InstantMessage", globals(),
                bundle_path=objc.pathForFramework(u'/System/Library/Frameworks/InstantMessage.framework'))

service = IMService.serviceWithName_('AIM')
print service.peopleWithScreenName_('pikswiss')

    Since Mac OS X 10.5 :

    from AddressBook import *

book = ABAddressBook.sharedAddressBook()
print book.me()
  39. Lock macOS screen
    python2.7 -c 'import sys,objc;from Foundation import NSBundle as nb;f="SACLockScreenImmediate";objc.loadBundleFunctions(nb.bundleWithPath_(sys.argv[1]),globals(),[(f,"@")]);exec(f+"()")' /S*/L*/P*/l*.f*

    Source: https://gist.github.com/pudquick/9797a9ce8ad97de6e326afc7c9894965 through @gorelics

  40. Mapping charsets
    # -*- coding: iso-8859-1 -*-

import string

french = "Peut-être cet été à la mer."

char_from = "éêà"
char_to   = "eea"

print french.translate(string.maketrans(char_from,char_to))

    Peut-etre cet ete a la mer.

  41. Multiple replace in one pass
    import re

def strTr( text, dic ):
    """ Replaces keys of dic with values of dic in text.
        2005-02 by Emanuel Rumpf """
    pat = "(%s)" % "|".join( map(re.escape, dic.keys())  )
    return re.sub( pat, lambda m:dic[m.group()], text )
  42. Multiprocessing in Python
    #!/bin/env python

from multiprocessing import Pool
import time

PARALLEL = 1

def f(x):
    print "start sleeping"
    time.sleep(1)
    print "end sleeping"
    return x

if __name__ == '__main__':

    l = xrange(15)

    if PARALLEL:
        pool = Pool()
        l2 = pool.map(f, l)
        pool.close()
        pool.join()
    else:
        l2 = map(f, l)

    print l2
  43. Offscreen Quartz drawing with Python

    #!/usr/bin/python

from AppKit import *

WIDTH = 128
HEIGHT = 64

def draw_something():
    p = NSBezierPath.bezierPath()

    p.moveToPoint_((10, 10))
    p.lineToPoint_((50, 60))
    p.lineToPoint_((110, 10))
    p.lineToPoint_((10, 10))

    NSColor.redColor().set()
    p.fill()

    NSColor.blueColor().set()
    p.stroke()

offscreenRep = NSBitmapImageRep.alloc().initWithBitmapDataPlanes_pixelsWide_pixelsHigh_bitsPerSample_samplesPerPixel_hasAlpha_isPlanar_colorSpaceName_bitmapFormat_bytesPerRow_bitsPerPixel_(None, WIDTH, HEIGHT, 8, 4, True, False, NSCalibratedRGBColorSpace, 0, 4 * WIDTH, 32)

context = NSGraphicsContext.graphicsContextWithBitmapImageRep_(offscreenRep)

NSGraphicsContext.setCurrentContext_(context)

#NSGraphicsContext.saveGraphicsState()

draw_something()

#NSGraphicsContext.restoreGraphicsState()

data = offscreenRep.representationUsingType_properties_(NSPNGFileType, None)

result = data.writeToFile_atomically_("img.png", True)
  44. OS X English Dictionary Lookup
    import DictionaryServices
s = "love"
print DictionaryServices.DCSCopyTextDefinition(None, s, (0,len(s)))

    love |lʌv| noun 1 a strong feeling of affection: ...

  45. Parse NSDate descriptions
    from datetime import datetime
from dateutil.parser import parse

print parse("Tue, 22 Jul 2008 08:17:41 +0200")

    2008-07-22 08:17:41+02:00

    or

    from dateutil.parser import parse
print parse("Tue, 22 Jul 2008 08:17:41 +0200")

    2008-07-22 08:17:41+02:00

  46. Pretty print JSON
    $ echo '{"foo": "lorem", "bar": "ipsum"}' | python -mjson.tool

    http://stackoverflow.com/questions/352098/how-to-pretty-print-json-script

  47. Pretty, local date and time
    from time import strftime
strftime("%Y-%m-%d %H:%M:%S")

    2016-08-27 14:09:48

  48. Python Image Library

    http://www.pythonware.com/products/pil/

    #!/usr/bin/python

import Image, ImageDraw

W = 255
H = 128

img = Image.new("RGB", (W, H), "black")
draw = ImageDraw.Draw(img)

for x in range(W):
    for y in range(H):
        color = (x % 255, y % 255, (x % (y+1)) % 255)
        draw.point((x,y), fill=color)

draw.line((0, H/2, W, H/2), "yellow")
draw.rectangle([(200, 60), (100, 120)], outline="#FF00FF")
draw.text((20, 40), "quickies.seriot.ch")

img.save("img.png", "PNG")
  49. Random element from sequence
    import random
random.choice(['a', 'b', 'c', 'd'])

    'b'

  50. Read a huge file line by line

    fileinput reads lines sequentially, but doesn't keep them in memory.

    import fileinput

for line in fileinput.input(['path']):
    print line
  51. Read an arbitrary line in a file
    import linecache
linecache.getline('/etc/passwd', 4)
  52. Read formatted datetime
    >>> import datetime

>>> datetime.datetime.strptime("20100225232300", "%Y%m%d%H%M%S")
datetime.datetime(2010, 2, 25, 23, 23)

    docs.python.org format documentation

  53. Reading binary data

    Reading two 2-byte integers and one 4-byte integer in big-endian format from a file:

    import struct

f = open(filename, "rb")
s = f.read(8)
x, y, z = struct.unpack(">hhl", s)

    The '>' in the format string forces big-endian data.

    The letter 'h' reads one "short integer" (2 bytes).

    The letter 'l' reads one "long integer" (4 bytes).

  54. Send an email

    and cheat where you can...

    #!/usr/bin/python
# -*- coding: iso-8859-1 -*-

import smtplib
import time

from_addr = "tintin@bluewin.ch"
to_addrs  = ["milou@vtx.ch"]
date = time.ctime(time.time())

msg = """From: "Georges W. Bush" <bush@whitehouse.gov>
Subject: Secret plan
Date: %s
To: "Donald Rumsfeld" <rumsfeld@whitehouse.gov>
X-Mailer: Apple Mail (2.733)

This is a test

é à
""" % date

s = smtplib.SMTP('smtp.bluewin.ch')

s.set_debuglevel(1)

s.sendmail(from_addr, to_addrs, msg)

s.quit()
  55. SFTP with the Paramiko module
    import paramiko # http://www.lag.net/paramiko/

USERNAME = ""
PASSWORD = ""
PATH_LOCAL = ""
PATH_REMOTE = ""

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect(host, username=USERNAME, password=PASSWORD)

ftp = ssh.open_sftp()
ftp.put(PATH_LOCAL, PATH_REMOTE)
ftp.close()
  56. Show keywords
    import keyword
keyword.kwlist

    ['and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'exec', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'not', 'or', 'pass', 'print', 'raise', 'return', 'try', 'while', 'with', 'yield']

  57. Show where a module lives
    >>> import cairo
>>> print(cairo)
<module 'cairo' from '/usr/local/lib/python3.9/site-packages/cairo/__init__.py'>

    Source: @nedbat

  58. Simulate enumerate type
    class State:
    UNKNOWN, WAKE, SLEEP = range(3)

state = State.UNKNOWN
  59. Singleton

    The following can be instanced several times, but all instances share the same state. Alex Martelli

    class Singleton:
    __shared_state = {}
    def __init__(self):
        self.__dict__ = self.__shared_state

    The following class returns the same instance for each instanciation.

    class Singleton(object):
    def __new__(type):
        if not '_the_instance' in type.__dict__:
            type._the_instance = object.__new__(type)
        return type._the_instance
  60. Sockets Datagrams

    server.py

    import socket

port = 8081
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.bind(("", port))
print "waiting on port:", port
while 1:
    data, addr = s.recvfrom(1024)
    print data

    client.py

    import socket

port = 8081
host = "localhost"
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.bind(("", 0))
s.sendto("Holy Guido! It's working.", (host, port))

    Source : Jeff Bauer

  61. Splitting a sequence into chunks
    s = "1234567890"
[s[i:i+3] for i in xrange(0, len(s), 3)]

    ['123', '456', '789', '0']

  62. Start a web server from current directory
    $ python -m SimpleHTTPServer 8080
  63. Static methods
    class C:

    def foo(x, y):
        print "staticmethod", x, y
    foo = staticmethod(foo)

C.foo(1, 2)
c = C()
c.foo(1, 2)

    Unifying types and classes in Python 2.2

  64. str.startswith() can accept a tuple of possible matches
    s = "asd"
s.startswith(('a','b','c'))

    True

  65. Strings concatenation

    Use this way, which takes a linear time:

    result = ''.join(strings)

    instead of this way, which takes a quadratic time:

    result = []
for s in strings:
    result += s
  66. Strip HTML tags
    import sgmllib

class Stripper(sgmllib.SGMLParser):
    def __init__(self):
        sgmllib.SGMLParser.__init__(self)

    def strip(self, some_html):
        self.theString = ""
        self.feed(some_html)
        self.close()
        return self.theString

    def handle_data(self, data):
        self.theString += data

stripper = Stripper()
print stripper.strip("<tag>asd</tag>")

    asd

  67. The Zen of Python
    >>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
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.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
  68. Unit tests
    #!/usr/bin/python

    """
    $ python tests.py
    $ python tests.py TestDemo
    $ python tests.py TestDemo.test_foo
    """

    import unittest

    class TestDemo(unittest.TestCase):

        def setUp(self):
            pass
            
        def tearDown(self):
            pass

        def test_foo(self):
            self.assertTrue('a' in 'asd')
            self.assertEqual(1+1, 2)
        
        def test_bar(self):
            pass

    if __name__ == '__main__':
        unittest.main()
  69. Use a shell command
    import subprocess
op = subprocess.check_output(["ls", "-al"])
print(op)
  70. Use named pipes
    #!/usr/bin/python

from subprocess import *
import os

FIFO_PATH = '/tmp/my_fifo'

if os.path.exists(FIFO_PATH):
    os.unlink(FIFO_PATH)

if not os.path.exists(FIFO_PATH):
    os.mkfifo(FIFO_PATH)
    my_fifo = open(FIFO_PATH, 'w+')
    print "my_fifo:", my_fifo

pipe = Popen('/bin/date', shell=False, stdin=PIPE, stdout=my_fifo, stderr=PIPE)

print open(FIFO_PATH, 'r').readline()

os.unlink(FIFO_PATH)
  71. Use requirements file

    Generate project requirements

    pip3 install pipreqs

pipreqs /path/to/project

    Then

    pip3 install -r requirements.txt
  72. uuid
    import uuid
uuid.uuid1()

    UUID('86e6df87-8546-11e1-aaeb-d49a20f5b3c2')

  73. Walk through a directory recursively
    import os

def all_files_from_path_gen(p):
    for root, dirs, files in os.walk(p):
        for d in dirs:
            for f in files:
                yield os.path.join(root, d, f)

for path in all_files_from_path_gen('.'):
    print path
  74. Write binary data
    import struct
import ctypes

bytes = ctypes.create_string_buffer(8)
struct.pack_into('i', bytes, 0, 10)
struct.pack_into('f', bytes, 4, 0.5)

f = open("file.dat", 'wb')
f.write(bytes)
f.close()

    result

    $ hexdump file.dat 
0000000 0a 00 00 00 00 00 00 3f                        
0000008
  75. Write to stderr
    import sys

sys.stderr.write("asd\n")
  76. XML-RPC web service

    server.py

    #!/usr/bin/python

from SimpleXMLRPCServer import *

class My_Web_Service:
    def __init__(self):
        pass

    # not callable through XML RPC because starts with '_'
    def _private(self):
        pass

    def add(self, x, y):
        return x + y

    def mul(self, x, y):
        return x * y

if __name__ == "__main__":
    server = SimpleXMLRPCServer(("localhost", 8080))
    server.register_instance(My_Web_Service())
    server.serve_forever()

    client.py

    #!/usr/bin/python

import xmlrpclib

server = xmlrpclib.Server('http://localhost:8080')

print server.add(3, 4)
print server.mul(3, 4)