加載器

加載器負(fù)責(zé)從諸如文件系統(tǒng)的資源加載模板。環(huán)境會(huì)把編譯的模塊像 Python 的sys.modules?一樣保持在內(nèi)存中。與?sys.models?不同，無(wú)論如何這個(gè) 緩存默認(rèn)有大小限制，且模板會(huì)自動(dòng)重新加載。 所有的加載器都是?BaseLoader?的子類。如果你想要?jiǎng)?chuàng)建自己的加載器，繼 承?BaseLoader?并重載?get_source?。

class?jinja2.BaseLoader

Baseclass for all loaders. Subclass this and override?get_source?to implement a custom loading mechanism. The environment provides a?get_template?method that calls the loader’s?load?method to get the?Template?object.

A very basic example for a loader that looks up templates on the file system could look like this:

from jinja2 import BaseLoader, TemplateNotFound
from os.path import join, exists, getmtime

class MyLoader(BaseLoader):

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

    def get_source(self, environment, template):
        path = join(self.path, template)
        if not exists(path):
            raise TemplateNotFound(template)
        mtime = getmtime(path)
        with file(path) as f:
            source = f.read().decode('utf-8')
        return source, path, lambda: mtime == getmtime(path)

get_source(environment,?template)

Get the template source, filename and reload helper for a template. It’s passed the environment and template name and has to return a tuple in the form(source,?filename,?uptodate)?or raise a?TemplateNotFound?error if it can’t locate the template.

The source part of the returned tuple must be the source of the template as unicode string or a ASCII bytestring. The filename should be the name of the file on the filesystem if it was loaded from there, otherwise?None. The filename is used by python for the tracebacks if no loader extension is used.

The last item in the tuple is the?uptodate?function. If auto reloading is enabled it’s always called to check if the template changed. No arguments are passed so the function must store the old state somewhere (for example in a closure). If it returns?False?the template will be reloaded.

load(environment,?name,?globals=None)

Loads a template. This method looks up the template in the cache or loads one by calling?get_source(). Subclasses should not override this method as loaders working on collections of other loaders (such as?PrefixLoader?or?ChoiceLoader) will not call this method but?get_source?directly.

這里有一個(gè) Jinja2 提供的內(nèi)置加載器的列表:

class?jinja2.FileSystemLoader(searchpath,?encoding='utf-8')

Loads templates from the file system. This loader can find templates in folders on the file system and is the preferred way to load them.

The loader takes the path to the templates as string, or if multiple locations are wanted a list of them which is then looked up in the given order:

>>> loader = FileSystemLoader('/path/to/templates')
>>> loader = FileSystemLoader(['/path/to/templates', '/other/path'])

Per default the template encoding is?'utf-8'?which can be changed by setting theencoding?parameter to something else.

class?jinja2.PackageLoader(package_name,?package_path='templates',?encoding='utf-8')

Load templates from python eggs or packages. It is constructed with the name of the python package and the path to the templates in that package:

loader = PackageLoader('mypackage', 'views')

If the package path is not given,?'templates'?is assumed.

Per default the template encoding is?'utf-8'?which can be changed by setting theencoding?parameter to something else. Due to the nature of eggs it’s only possible to reload templates if the package was loaded from the file system and not a zip file.

class?jinja2.DictLoader(mapping)

Loads a template from a python dict. It’s passed a dict of unicode strings bound to template names. This loader is useful for unittesting:

>>> loader = DictLoader({'index.html': 'source here'})

Because auto reloading is rarely useful this is disabled per default.

class?jinja2.FunctionLoader(load_func)

A loader that is passed a function which does the loading. The function becomes the name of the template passed and has to return either an unicode string with the template source, a tuple in the form?(source,?filename,?uptodatefunc)?or?None?if the template does not exist.

>>> def load_template(name):
...     if name == 'index.html':
...         return '...'
...
>>> loader = FunctionLoader(load_template)

The?uptodatefunc?is a function that is called if autoreload is enabled and has to returnTrue?if the template is still up to date. For more details have a look atBaseLoader.get_source()?which has the same return value.

class?jinja2.PrefixLoader(mapping,?delimiter='/')

A loader that is passed a dict of loaders where each loader is bound to a prefix. The prefix is delimited from the template by a slash per default, which can be changed by setting the?delimiter?argument to something else:

loader = PrefixLoader({
    'app1':     PackageLoader('mypackage.app1'),
    'app2':     PackageLoader('mypackage.app2')
})

By loading?'app1/index.html'?the file from the app1 package is loaded, by loading'app2/index.html'?the file from the second.

class?jinja2.ChoiceLoader(loaders)

This loader works like the?PrefixLoader?just that no prefix is specified. If a template could not be found by one loader the next one is tried.

>>> loader = ChoiceLoader([
...     FileSystemLoader('/path/to/user/templates'),
...     FileSystemLoader('/path/to/system/templates')
... ])

This is useful if you want to allow users to override builtin templates from a different location.

class?jinja2.ModuleLoader(path)

This loader loads templates from precompiled templates.

Example usage:

>>> loader = ChoiceLoader([
...     ModuleLoader('/path/to/compiled/templates'),
...     FileSystemLoader('/path/to/templates')
... ])

Templates can be precompiled with?Environment.compile_templates().