speaklater 1.3

implements a lazy string for python useful for use with gettext

A module that provides lazy strings for translations. Basically you get an object that appears to be a string but changes the value every time the value is evaluated based on a callable you provide.

For example you can have a global lazy_gettext function that returns a lazy string with the value of the current set language.

Example:

>>> from speaklater import make_lazy_string
>>> sval = u'Hello World'
>>> string = make_lazy_string(lambda: sval)

This lazy string will evaluate to the value of the sval variable.

>>> string
lu'Hello World'
>>> unicode(string)
u'Hello World'
>>> string.upper()
u'HELLO WORLD'

If you change the value, the lazy string will change as well:

>>> sval = u'Hallo Welt'
>>> string.upper()
u'HALLO WELT'

This is especially handy when combined with a thread local and gettext translations or dicts of translatable strings:

>>> from speaklater import make_lazy_gettext
>>> from threading import local
>>> l = local()
>>> l.translations = {u'Yes': 'Ja'}
>>> lazy_gettext = make_lazy_gettext(lambda: l.translations.get)
>>> yes = lazy_gettext(u'Yes')
>>> print yes
Ja
>>> l.translations[u'Yes'] = u'Si'
>>> print yes
Si

Lazy strings are no real strings so if you pass this sort of string to a function that performs an instance check, it will fail. In that case you have to explicitly convert it with unicode and/or string depending on what string type the lazy string encapsulates.

To check if a string is lazy, you can use the is_lazy_string function:

>>> from speaklater import is_lazy_string
>>> is_lazy_string(u'yes')
False
>>> is_lazy_string(yes)
True

New in version 1.2: It’s now also possible to pass keyword arguments to the callback used with make_lazy_string.