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OO

Basic Modern Class

class ClassName(object):

    def __init__(self, foo):
        self.foo = foo

    @classmethod
    def bar(cls, arg):
        ...

Super Call

def foo(self, bar):
    return super(MyClass, self).foo(bar)

Recursive Subclass Map

@classmethod
def subclass_map(cls):
    map = {c.__name__: c for c in cls.__subclasses__()}
    for subclass in map.values():
        map.update(subclass.subclass_map())
    return map

HTTP

HEAD request

request = urllib2.Request(url)
request.get_method = lambda : 'HEAD'
response = urllib2.urlopen(request)
print response.info()['Last-Modified']

Slurp page

url = 'http://www.sno.phy.queensu.ca/~phil/exiftool/'
request = urllib2.Request(url)
response = urllib2.urlopen(request)
data = response.read()

Installing Modules

PIP

http://www.pip-installer.org/en/latest/installing.html
curl https://raw.github.com/pypa/pip/master/contrib/get-pip.py | sudo python

sudo -H python -m ensurepip

SciPy

http://fonnesbeck.github.com/ScipySuperpack/

Date/Time

Sleep

time.sleep(seconds)

Now

dt = datetime.datetime.now()

Time some code

t1 = datetime.datetime.now()
xxx
t2 = datetime.datetime.now()
print '{:0.1f}s'.format((t2 - t1).total_seconds())

Convert RFC-style date/time to datetime

modification_time = datetime.datetime(*email.utils.parsedate(urllib2_response.info()['Last-Modified'])[:6])

Convert ISO timestamp to datetime

datetime.datetime.strptime("2008-09-03T20:56:35.450686Z", "%Y-%m-%dT%H:%M:%S.%fZ")

Touch file modification with datetime

timestamp = time.mktime(some_datetime.timetuple())
os.utime(file_path, (timestamp, timestamp))

Get file modification timestamp as datetime

datetime.datetime.fromtimestamp(os.stat(path).st_mtime)

Time delta between datetimes

t1 = datetime.datetime.now()
...
age_seconds = (datetime.datetime.now() - t1).seconds

Human Readable Timestamp

datetime.datetime.now().strftime('%Y%m%d-%H%M%S')

Datetime instance to Unix Timestamp

import datetime
date = datetime.datetime.utcfromtimestamp(0)

def unix_time_millis(dt):
    return (dt - epoch).total_seconds() * 1000.0

Unix timestamp to UTC and Local Time

import datetime
utcdatetime = datetime.datetime.utcfromtimestamp(unix_timestamp)
localdatetime = datetime.datetime.fromtimestamp(unix_timestamp)

Get Computer's UTC Offset

http://stackoverflow.com/a/3168394/182781

Exceptions

Raise Exception

raise Exception('foo')

Less noisy exception errors

try:
    ...
except Exception as e:
    print ''.join(traceback.format_exception(*sys.exc_info())[1:-2])
    print ANSIColor.wrap(str(e), color=ANSIColor.red)

Shell Command

status = subprocess.call(['git', 'status', '--porcelain', self.path])
status = subprocess.check_call(['git', 'status', '--porcelain', self.path])
output = subprocess.check_output(['git', 'status', '--porcelain', self.path])

sudo authenticate

def validate_sudo():
    pwd = ''
    for i in range(5):
        sp = subprocess.Popen(['sudo', '-S', '-v'], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        sp.communicate(pwd + '\n')
        if sp.returncode == 0:
            return True
        pwd = getpass.getpass()
    return False

relaunch with sudo

@classmethod
def ensure_superuser(cls):
    if os.getuid() != 0:
        print 'Relaunching with sudo...'
        os.execv('/usr/bin/sudo', ['/usr/bin/sudo'] + sys.argv)

Context Manager for with Statement

@contextlib.contextmanager
def chdir_to_path(self, path):
    oldwd = os.getcwd()
    os.chdir(path)
    try:
        yield
    except:
        os.chdir(oldwd)
        raise

    os.chdir(oldwd)

def foo(self):
    with self.chdir_to_path(self.path):
        foo

Logging

Basic Logging Setup

import logging
logging.basicConfig(level=logging.DEBUG)

logging.debug('foo')
logging.warning('foo')
logging.error('foo')

Based on args:

if self.args.verbose:
    logging.basicConfig(level=logging.DEBUG)

Files

Slurp File Contents

with open('x.txt') as x: f = x.read()
with open('x.txt') as x: f = x.readlines()

Walking File System Trees

for dirpath, dirnames, filenames in os.walk(path, topdown=True):
    ...

Get directory contents

contents = os.listdir(path)

Autopep

pep8 file.py

diff

autopep8 -d --ignore E501 file.py

in-place

autopep8 -i --ignore E501 file.py

Regex

Single match

match = re.search(r'pattern', string)
print match.group(1)

Iterate

for match in re.finditer(r'pattern', string)
    print match.group(1)

Replace

re.sub(r'pattern', replace, string)

String Manipulations

Split string into lines

str.splitlines()

Convert camel case to underscore

def underscore_to_camel_case(underscore_value):
    return re.sub(r'(\w)_(\w)', lambda match: match.group(1) + match.group(2).upper(), underscore_value)

def camel_case_to_underscore(camelcase_value):
    return re.sub(r'([a-z])([A-Z])', lambda match: match.group(1) + '_' + match.group(2).lower(), camelcase_value)

String Formatting

Fixed-width aligned placeholder

'foo [{:<5}] bar'.format(value)

Parameter-defined, fixed-width placeholder

'foo [{1:<{0}}] bar'.format(field_width, value)

Empty a list in-place

del list[:]

http://docs.python.org/2/tutorial/datastructures.html#the-del-statement

Iterate over a dictionary's keys and values

for k, v in globals().items():
    ...

Iterate over a collection with an index

for index, item in enumerate(iterable):
    ...

Version Number Sorting

versions = [tuple(map(int, (i.split('.')))) for i in version_strings]
sorted(versions, cmp)

Support in pkg_resources (http://stackoverflow.com/questions/11887762/compare-version-strings):

import pkg_resources
pkg_resources.parse_version('1.2.3') < pkg_resources.parse_version('4.5.6')

Dictionary get with fallback

dict.get(key, default)

Object get with fallback

getattr(object, key, default)

Iterate over slices

for i in range(0, len(items), 50):
    x = items[i:i + 50]

Encoding / Unicode / Charsets

Decode Hex Chars

'cafebabe'.decode('hex')
binascii.unhexlify('cafebabe')
binascii.a2b_hex('cafebabe')

Encode Hex Chars

binascii.b2a_hex(binary)
binascii.hexlify(binary)

Shell Script Inline Python script

python <<EOF
from IPython.external.mathjax import install_mathjax
install_mathjax()
EOF

Get file system path to current file

os.path.dirname(os.path.abspath(inspect.getfile(inspect.currentframe())))

Plist parsing with plistlib

data = plistlib.readPlistFromString(stdoutdata)

XML with ElementTree

import xml.etree.ElementTree

Parse File

tree = xml.etree.ElementTree.parse(path)

Parse String

tree = xml.etree.ElementTree.fromstring(xml_string)

PyObjc

Loading Frameworks - old

http://quickies.seriot.ch/index.php?id=180

import objc

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

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

Loading Frameworks - Since Mac OS X 10.5

from AddressBook import *

book = ABAddressBook.sharedAddressBook()
print book.me()

Replace otool on OS X Systems without Xcode

The macholib module can replace otool for some purposes, for example getting a binary's UUID:

Replace

otool -l /Applications/Foo.app/Contents/MacOS/Foo | grep uuid

with

python -c 'import macholib.MachO, uuid, sys; binary = macholib.MachO.MachO(sys.argv[1]); uuid_command, = [c[1] for c in binary.headers[0].commands if type(c[1]) == macholib.mach_o.uuid_command]; print uuid.UUID(bytes=uuid_command.uuid)' /Applications/Foo.app/Contents/MacOS/Foo

or

python - /Applications/Foo.app/Contents/MacOS/Foo <<-EOF
    import macholib.MachO, uuid, sys
    binary = macholib.MachO.MachO(sys.argv[1])
    uuid_command, = [c[1] for c in binary.headers[0].commands if type(c[1]) == macholib.mach_o.uuid_command]
    print uuid.UUID(bytes=uuid_command.uuid)
EOF

C API

Print description of an object in an embedded Python 3 interpreter when attached with LLDB:

call (char *)PyUnicode_AsUTF8((void *)PyObject_Repr($arg2))