speaklater3

speaklater

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, text_type
>>> sval = u'Hello World'
>>> string = make_lazy_string(lambda: sval)

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

>>> string
l'Hello World'
>>> text_type(string) == u'Hello World'
True
>>> string.upper() == u'HELLO WORLD'
True

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

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

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 1.4: python >= 3.3 (and also 2.6 and 2.7) support,
                    repr(lazystring) is l"foo" on py2 and py3 - no "u" on py2!

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