developer toolbox » python

s obzirom da python godinama nisam ni pogledao, ovdje ću bilježiti nepoznate stvari na koje naletim u openerp kodu.

• quick python book second edition, vernon L. Ceder, manning publications
• internet

lambda expressions¶

base_vat

def mult_add(i, j):
    """Sum each digits of the multiplication of i and j.""" 
    return reduce(lambda x, y: x + int(y), str(i*j), 0

evo nešto jednostavnije

>>> l1 = lambda deg_f: 273.15 + (deg_f - 32) * 5/9
>>> l1(32)
273.14999999999998

oni koji znaju clipper, lambda je najsličniji kodnom bloku.

reduce(function, iterable[, initializer])

    Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). The left argument, x, is the accumulated value and the right argument, y, is the update value from the iterable. If the optional initializer is present, it is placed before the items of the iterable in the calculation, and serves as a default when the iterable is empty. If initializer is not given and iterable contains only one item, the first item is returned.

>>> l2 = lambda x, y: x+y
>>> l2(1,2)
3
>>> reduce(l2, [1,2,3,4,5])
15

aha kontam

prvo je bilo 1+2 = 3, pa je onda lambdi prosljeđeno to 3 + sljedeći argument 3 = 6, pa 6 + 4 = 10, pa 10 + 5 = 15

kontam cool stvar

utf-8 encoding¶

http://evanjones.ca/python-utf8.html

čitaj

>>> import codecs
>>> fileObj = codecs.open("test.txt", "r", "utf-8")
>>> u = fileObj.read()
>>> print u
Ernad Husremović

piši

>>> outFile = file( "test_2.txt", "w")
>>> outFile.write( codecs.BOM_UTF8)
>>> unicodeString=u'Ernad Husremovićć ŠŽĐ'
>>> outFile.write( unicodeString.encode( "utf-8" ))
>>> outFile.close()
>>> import os
>>> os.system("cat test_2.txt")
Ernad Husremovićć ŠŽĐ0

unicode vs str¶

>>> str
'ernad husremovi\xc4\x87'
>>> u_str
u'ernad husremovi\u0107'
>>> str
'ernad husremovi\xc4\x87'
>>> u_str.__class__.__name__
'unicode'
>>> str.__class__.__name__
'str'

>>> u_str
u'ernad husremovi\u0107'
>>> binascii.a2b_uu(binascii.b2a_uu(u_str.encode('utf-8'))).decode('utf-8')
u'ernad husremovi\u0107'

encoding decoding¶

http://docs.python.org/library/codecs.html

Unicode strings are stored internally as sequences of codepoints (to be precise as Py_UNICODE arrays). Depending on the way Python is compiled (either via --enable-unicode=ucs2 or --enable-unicode=ucs4, with the former being the default) Py_UNICODE is either a 16-bit or 32-bit data type. Once a Unicode object is used outside of CPU and memory, CPU endianness and how these arrays are stored as bytes become an issue. Transforming a unicode object into a sequence of bytes is called encoding and recreating the unicode object from the sequence of bytes is known as decoding. There are many different methods for how this transformation can be done (these methods are also called encodings). The simplest method is to map the codepoints 0-255 to the bytes 0x0-0xff. This means that a unicode object that contains codepoints above U+00FF can’t be encoded with this method (which is called 'latin-1' or 'iso-8859-1'). unicode.encode() will raise a UnicodeEncodeError that looks like this: UnicodeEncodeError: 'latin-1' codec can't encode character u'\u1234' in position 3: ordinal not in range(256).

>>> f=open('test.txt', 'rb')
>>> str=f.read()
>>> str
'\xc4\x8c\xc4\x87\n'
>>> type(str)
<type 'str'>
>>> str.decode('utf-8')
u'\u010c\u0107\n'
>>> print str.decode('utf-8')
Čć

http://stackoverflow.com/questions/2611205/how-do-i-write-raw-binary-data-in-python

If you need a 1:1 mapping from arbitrary bytes to unicode:

Pass data.decode('latin1') to the codec. latin1 maps bytes 0-255 to unicode characters 0-255, which is kinda elegant.

The codec will, of course, encode your characters - 128-255 are encoded as 2 or 3 bytes in UTF-8 (surprisingly, the average overhead is 50%, more than base64!). This quite kills the "elegance" of having a 1:1 mapping.

Note also that unicode characters 0-255 include nasty invisible/control characters (newline, formfeed, soft hyphen, etc.) making your binary data annoying to view in text editors.

Considering these drawbacks, I do not recommend latin1 unless you understand exactly why you want it.
I'm just mentioning it as the other "natural" encoding that springs to mind.

h2.sys.path

>>> import sys
>>> sys.path
['', '/usr/local/lib/python2.6/dist-packages/psycopg2-2.3.0_beta1-py2.6-linux-x86_64.egg', '/usr/local/lib/python2.6/dist-packages/reportlab-2.5-py2.6-linux-x86_64.egg', '/usr/local/lib/python2.6/dist-packages/pydot-1.0.3-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/pyparsing-1.5.5-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/pytz-2010o-py2.6.egg', '/usr/lib/python2.6/dist-packages/PIL', '/usr/local/lib/python2.6/dist-packages/vobject-0.8.1c-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/python_dateutil-1.5-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/lxml-2.3beta1-py2.6-linux-x86_64.egg', '/usr/local/lib/python2.6/dist-packages/PyYAML-3.09-py2.6-linux-x86_64.egg', '/usr/local/lib/python2.6/dist-packages/openerp_web-6.0.0_rc1-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/FormEncode-1.2.3dev-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/Babel-0.9.5-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/CherryPy-3.1.2-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/xlwt-0.7.2-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/numpy-1.5.1-py2.6-linux-x86_64.egg', '/usr/local/lib/python2.6/dist-packages/matplotlib-1.0.0-py2.6-linux-x86_64.egg', '/usr/local/lib/python2.6/dist-packages/openerp_client-6.0.0_rc1_1-py2.6.egg', '/usr/lib/python2.6', '/usr/lib/python2.6/plat-linux2', '/usr/lib/python2.6/lib-tk', '/usr/lib/python2.6/lib-old', '/usr/lib/python2.6/lib-dynload', '/usr/local/lib/python2.6/dist-packages', '/usr/lib/python2.6/dist-packages', '/usr/lib/python2.6/dist-packages/gst-0.10', '/usr/lib/pymodules/python2.6', '/usr/lib/python2.6/dist-packages/gtk-2.0', '/usr/lib/pymodules/python2.6/gtk-2.0', '/usr/lib/python2.6/dist-packages/wx-2.8-gtk2-unicode']

http://mohsinpage.wordpress.com/category/python/

http://redmine.bring.out.ba/issues/21924#note-9