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Python extension wrapping the ICU C++ API

Project description

README file for PyICU


- Welcome
- Building PyICU
- Running PyICU
- What's available
- API Documentation


Welcome to PyICU, a Python extension wrapping IBM's International
Components for Unicode C++ library (ICU).

PyICU is a project maintained by the Open Source Applications Foundation.

IBM's ICU homepage is:

Building PyICU

Before building PyICU the ICU 3.6 or 3.8 libraries must be built and
installed. Refer to each system's instructions for more information.

As of version 0.5 PyICU no longer uses SWIG.

As of version 0.8 PyICU is built with distutils or setuptools:
- verify that the INCLUDES, LFLAGS, CFLAGS and LIBRARIES dictionaries in contain correct values for your platform
- python build
- sudo python install

Running PyICU

. Mac OS X
Make sure that DYLD_LIBRARY_PATH contains paths to the directory(ies)
containing the ICU libs.

. Linux
Make sure that LD_LIBRARY_PATH contains paths to the directory(ies)
containing the ICU libs or that you added the corresponding -rpath
argument to LFLAGS.

. Windows
Make sure that PATH contains paths to the directory(ies)
containing the ICU DLLs.

What's available

PyICU is under active development. Currently, the string, locale, format,
calendar, timezone, charset and various iterator classes are available.
See the CHANGES file for an up to date log of changes and additions.

API Documentation

At the moment, there is no API documentation for PyICU. The API for ICU is
documented at and the following
patterns can be used to translate from the C++ APIs to the corresponding
Python APIs.

- strings

The ICU string type, UnicodeString, is a type pointing at a mutable
array of UChar Unicode 16-bit wide characters. The Python unicode type
is an immutable string of 16-bit or 32-bit wide Unicode characters.

Because of these differences, UnicodeString and Python's unicode type
are not merged into the same type when crossing the C++ boundary.
ICU APIs taking UnicodeString arguments have been overloaded to also
accept Python str or unicode type arguments. In the case of str objects,
utf-8 encoding is assumed when converting them to UnicodeString

To convert a Python str encoded in a encoding other than utf-8 to an ICU
UnicodeString use the UnicodeString(str, encodingName) constructor.

ICU's C++ APIs accept and return UnicodeString arguments in several
ways: by value, by pointer or by reference.
When an ICU C++ API is documented to accept a UnicodeString & parameter,
it is safe to assume that there are several corresponding PyICU python
APIs making it accessible in simpler ways:
For example, the 'UnicodeString &Locale::getDisplayName(UnicodeString &)'
API, documented here:
can be invoked from Python in several ways:

1. The ICU way

>>> from PyICU import UnicodeString, Locale
>>> locale = Locale('pt_BR')
>>> string = UnicodeString()
>>> name = locale.getDisplayName(string)
>>> name
<UnicodeString: Portuguese (Brazil)>
>>> name is string
True <-- string arg was returned, modified in place

2. The Python way

>>> from PyICU import Locale
>>> locale = Locale('pt_BR')
>>> name = locale.getDisplayName()
>>> name
<UnicodeString: Portuguese (Brazil)>

A UnicodeString object was allocated for Python and returned.

A UnicodeString can be coerced to a Python unicode string with Python's
unicode() constructor. The usual len(), str(), comparison, [] and [:]
operators are all available, with the additional twists that slicing is
not read-only and that += is also available since a UnicodeString is
mutable. For example:

>>> name = locale.getDisplayName()
<UnicodeString: Portuguese (Brazil)>
>>> unicode(name)
u'Portuguese (Brazil)'
>>> len(name)
>>> str(name) <-- works when chars fit with default encoding
'Portuguese (Brazil)'
>>> name[3]
>>> name[12:18]
<UnicodeString: Brazil>
>>> name[12:18] = 'the country of Brasil'
>>> name
<UnicodeString: Portuguese (the country of Brasil)>
>>> name += ' oh joy'
>>> name
<UnicodeString: Portuguese (the country of Brasil) oh joy>

- error reporting

The C++ ICU library does not use C++ exceptions to report errors. ICU
C++ APIs return errors via a UErrorCode reference argument. All such
APIs are wrapped by Python APIs that omit this argument and throw an
ICUError Python exception instead. The same is true for ICU APIs taking
both a ParseError and a UErrorCode, they are both to be omitted.

For example, the 'UnicodeString &DateFormat::format(const Formattable &,
UnicodeString &, UErrorCode &)' API, documented here
is invoked from Python with:

>>> from PyICU import DateFormat, Formattable
>>> df = DateFormat.createInstance()
>>> df
<SimpleDateFormat: M/d/yy h:mm a>
>>> f = Formattable(940284258.0, Formattable.kIsDate)
>>> df.format(f)
<UnicodeString: 10/18/99 3:04 PM>

Of course, the simpler 'UnicodeString &DateFormat::format(UDate,
UnicodeString &)' documented here:
can be used too:

>>> from PyICU import DateFormat
>>> df = DateFormat.createInstance()
>>> df
<SimpleDateFormat: M/d/yy h:mm a>
>>> df.format(940284258.0)
<UnicodeString: 10/18/99 3:04 PM>

- dates

ICU uses a double floating point type called UDate that represents the
number of milliseconds elapsed since 1970-jan-01 UTC for dates.

In Python, the value returned by the time module's time() function is
the number of seconds since 1970-jan-01 UTC. Because of this difference,
floating point values are multiplied by 1000 when passed to APIs taking
UDate and divided by 1000 when returned as UDate.

Python's datetime objects, with or without timezone information, can
also be used with APIs taking UDate arguments. The datetime objects get
converted to UDate when crossing into the C++ layer.

- arrays

Many ICU API take array arguments. A list of elements of the array
element types is to be passed from Python.

- StringEnumeration

An ICU StringEnumeration has three 'next' methods: next() which returns
a 'str' objects, unext() which returns 'unicode' objects and snext()
which returns 'UnicodeString' objects.
Any of these methods can be used as an iterator, using the Python
built-in 'iter' function.

For example, let e be a StringEnumeration instance:

[s for s in e] is a list of 'str' objects
[s for s in iter(e.unext, None)] is a list of 'unicode' objects
[s for s in iter(e.snext, None)] is a list of 'UnicodeString' objects

- timezones

The ICU TimeZone type may be wrapped with an ICUtzinfo type for usage
with Python's datetime type. For example:

tz = ICUtzinfo(TimeZone.createTimeZone('US/Mountain'))

or, even simpler:

tz = ICUtzinfo.getInstance('Pacific/Fiji')

To get the default time zone use:

defaultTZ = ICUtzinfo.getDefault()

To get the time zone's id, use the 'tzid' attribute or coerce the time
zone to a string:

ICUtzinfo.getInstance('Pacific/Fiji').tzid -> 'Pacific/Fiji'
str(ICUtzinfo.getInstance('Pacific/Fiji')) -> 'Pacific/Fiji'

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