This section describes the Python API for Mako templates. If you are using Mako within a web framework such as Pylons, the work of integrating Mako's API is already done for you, in which case you can skip to the next section, Syntax.
The most basic way to create a template and render it is through the Template class:
from mako.template import Template
mytemplate = Template("hello world!")
print mytemplate.render()
Above, the text argument to Template is compiled into a Python module representation. This module contains a function called render_body(), which produces the output of the template. When mytemplate.render() is called, Mako sets up a runtime environment for the template and calls the render_body() function, capturing the output into a buffer and returning its string contents.
The code inside the render_body() function has access to a namespace of variables. You can specify these variables by sending them as additional keyword arguments to the render() method:
from mako.template import Template
mytemplate = Template("hello, ${name}!")
print mytemplate.render(name="jack")
The template.render() method calls upon Mako to create a Context object, which stores all the variable names accessible to the template and also stores a buffer used to capture output. You can create this Context yourself and have the template render with it, using the render_context method:
from mako.template import Template
from mako.runtime import Context
from StringIO import StringIO
mytemplate = Template("hello, ${name}!")
buf = StringIO()
ctx = Context(buf, name="jack")
mytemplate.render_context(ctx)
print buf.getvalue()
A Template can also load its template source code from a file, using the filename keyword argument:
from mako.template import Template
mytemplate = Template(filename='/docs/mytmpl.txt')
print mytemplate.render()
For improved performance, a Template which is loaded from a file can also cache the source code to its generated module on the filesystem as a regular Python module file (i.e. a .py file). To do this, just add the module_directory argument to the template:
from mako.template import Template
mytemplate = Template(filename='/docs/mytmpl.txt', module_directory='/tmp/mako_modules')
print mytemplate.render()
When the above code is rendered, a file /tmp/mako_modules/docs/mytmpl.txt.py is created containing the source code for the module. The next time a Template with the same arguments is created, this module file will be automatically re-used.
All of the examples thus far have dealt with the usage of a single Template object. If the code within those templates tries to locate another template resource, it will need some way to find them, using simple URI strings. For this need, the resolution of other templates from within a template is accomplished by the TemplateLookup class. This class is constructed given a list of directories in which to search for templates, as well as keyword arguments that will be passed to the Template objects it creates.
from mako.template import Template
from mako.lookup import TemplateLookup
mylookup = TemplateLookup(directories=['/docs'])
mytemplate = Template("""<%include file="header.txt"/> hello world!""", lookup=mylookup)
Above, we created a textual template which includes the file header.txt. In order for it to have somewhere to look for header.txt, we passed a TemplateLookup object to it, which will search in the directory /docs for the file header.txt.
Usually, an application will store most or all of its templates as text files on the filesystem. So far, all of our examples have been a little bit contrived in order to illustrate the basic concepts. But a real application would get most or all of its templates directly from the TemplateLookup, using the aptly named get_template method, which accepts the URI of the desired template:
from mako.template import Template
from mako.lookup import TemplateLookup
mylookup = TemplateLookup(directories=['/docs'], module_directory='/tmp/mako_modules')
def serve_template(templatename, **kwargs):
mytemplate = mylookup.get_template(templatename)
print mytemplate.render(**kwargs)
In the example above, we create a TemplateLookup which will look for templates in the /docs directory, and will store generated module files in the /tmp/mako_modules directory. The lookup locates templates by appending the given URI to each of its search directories; so if you gave it a URI of /etc/beans/info.txt, it would search for the file /docs/etc/beans/info.txt, else raise a TopLevelNotFound exception, which is a custom Mako exception.
When the lookup locates templates, it will also assign a uri property to the Template which is the uri passed to the get_template() call. Template uses this uri to calculate the name of its module file. So in the above example, a templatename argument of /etc/beans/info.txt will create a module file /tmp/mako_modules/etc/beans/info.txt.py.
The TemplateLookup also serves the important need of caching a fixed set of templates in memory at a given time, so that successive uri lookups do not result in full template compilations and/or module reloads on each request. By default, the TemplateLookup size is unbounded. You can specify a fixed size using the collection_size argument:
mylookup = TemplateLookup(directories=['/docs'],
module_directory='/tmp/mako_modules', collection_size=500)
The above lookup will continue to load templates into memory until it reaches a count of around 500. At that point, it will clean out a certain percentage of templates using a least recently used scheme.
back to section topAnother important flag on TemplateLookup is filesystem_checks. This defaults to True, and says that each time a template is returned by the get_template() method, the revision time of the original template file is checked against the last time the template was loaded, and if the file is newer will reload its contents and recompile the template. On a production system, setting filesystem_checks to False can afford a small to moderate performance increase (depending on the type of filesystem used).
Both Template and TemplateLookup accept output_encoding and encoding_errors parameters which can be used to encode the output in any Python supported codec:
from mako.template import Template
from mako.lookup import TemplateLookup
mylookup = TemplateLookup(directories=['/docs'], output_encoding='utf-8', encoding_errors='replace')
mytemplate = mylookup.get_template("foo.txt")
print mytemplate.render()
When using Python 3, the render() method will return a bytes object, if output_encoding is set. Otherwise it returns a string.
Additionally, the render_unicode() method exists which will return the template output as a Python unicode object, or in Python 3 a string:
print mytemplate.render_unicode()
The above method disregards the output encoding keyword argument; you can encode yourself by saying:
print mytemplate.render_unicode().encode('utf-8', 'replace')
Note that Mako's ability to return data in any encoding and/or unicode implies that the underlying output stream of the template is a Python unicode object. This behavior is described fully in The Unicode Chapter.
Template exceptions can occur in two distinct places. One is when you lookup, parse and compile the template, the other is when you run the template. Within the running of a template, exceptions are thrown normally from whatever Python code originated the issue. Mako has its own set of exception classes which mostly apply to the lookup and lexer/compiler stages of template construction. Mako provides some library routines that can be used to help provide Mako-specific information about any exception's stack trace, as well as formatting the exception within textual or HTML format. In all cases, the main value of these handlers is that of converting Python filenames, line numbers, and code samples into Mako template filenames, line numbers, and code samples. All lines within a stack trace which correspond to a Mako template module will be converted to be against the originating template file.
To format exception traces, the text_error_template and html_error_template functions are provided. They make usage of sys.exc_info() to get at the most recently thrown exception. Usage of these handlers usually looks like:
from mako import exceptions
try:
template = lookup.get_template(uri)
print template.render()
except:
print exceptions.text_error_template().render()
Or for the HTML render function:
from mako import exceptions
try:
template = lookup.get_template(uri)
print template.render()
except:
print exceptions.html_error_template().render()
The html_error_template template accepts two options: specifying full=False causes only a section of an HTML document to be rendered. Specifying css=False will disable the default stylesheet from being rendered.
E.g.:
print exceptions.html_error_template().render(full=False)
The HTML render function is also available built-in to Template using the format_exceptions flag. In this case, any exceptions raised within the render stage of the template will result in the output being substituted with the output of html_error_template.
template = Template(filename="/foo/bar", format_exceptions=True)
print template.render()
Note that the compile stage of the above template occurs when you construct the Template itself, and no output stream is defined. Therefore exceptions which occur within the lookup/parse/compile stage will not be handled and will propagate normally. While the pre-render traceback usually will not include any Mako-specific lines anyway, it will mean that exceptions which occur previous to rendering and those which occur within rendering will be handled differently...so the try/except patterns described previously are probably of more general use.
The underlying object used by the error template functions is the RichTraceback object. This object can also be used directly to provide custom error views. Here's an example usage which describes its general API:
from mako.exceptions import RichTraceback
try:
template = lookup.get_template(uri)
print template.render()
except:
traceback = RichTraceback()
for (filename, lineno, function, line) in traceback.traceback:
print "File %s, line %s, in %s" % (filename, lineno, function)
print line, "\n"
print "%s: %s" % (str(traceback.error.__class__.__name__), traceback.error)
Further information about RichTraceback is available within the module-level documentation for mako.exceptions.
The Mako distribution includes a little bit of helper code for the purpose of using Mako in some popular web framework scenarios. This is a brief description of whats included.
The standard plugin methodology used by Turbogears as well as Pylons is included in the module mako.ext.turbogears, using the TGPlugin class. This is also a setuptools entrypoint under the heading python.templating.engines with the name mako.
A sample WSGI application is included in the distrubution in the file examples/wsgi/run_wsgi.py. This runner is set up to pull files from a templates as well as an htdocs directory and includes a rudimental two-file layout. The WSGI runner acts as a fully functional standalone web server, using wsgiutils to run itself, and propagates GET and POST arguments from the request into the Context, can serve images, css files and other kinds of files, and also displays errors using Mako's included exception-handling utilities.
A Pygments-compatible syntax highlighting module is included under mako.ext.pygmentplugin. This module is used in the generation of Mako documentation and also contains various setuptools entry points under the heading pygments.lexers, including mako, html+mako, xml+mako (see the setup.py file for all the entry points).
Mako provides support for extracting gettext messages from templates via a Babel extractor entry point under mako.ext.babelplugin.
Gettext messages are extracted from all Python code sections, even the more obscure ones such as control structures, def tag function declarations, call tag exprs and even page tag args.
Translator comments may also be extracted from Mako templates when a comment tag is specified to Babel (such as with the -c option).
For example, a project 'myproj' contains the following Mako template at myproj/myproj/templates/name.html:
<div id="name">
Name:
## TRANSLATORS: This is a proper name. See the gettext
## manual, section Names.
${_('Francois Pinard')}
</div>
To extract gettext messages from this template the project needs a Mako section in its Babel Extraction Method Mapping file (typically located at myproj/babel.cfg):
# Extraction from Python source files
[python: myproj/**.py]
# Extraction from Mako templates
[mako: myproj/templates/**.html]
input_encoding = utf-8
The Mako extractor supports an optional input_encoding parameter specifying the encoding of the templates (identical to Template/TemplateLookup's input_encoding parameter).
Invoking Babel's extractor at the command line in the project's root directory:
myproj$ pybabel extract -F babel.cfg -c "TRANSLATORS:" .
Will output a gettext catalog to stdout including the following:
#. TRANSLATORS: This is a proper name. See the gettext
#. manual, section Names.
#: myproj/templates/name.html:5
msgid "Francois Pinard"
msgstr ""
This is only a basic example: Babel can be invoked from setup.py and its command line options specified in the accompanying setup.cfg via Babel Distutils/Setuptools Integration.
Comments must immediately precede a gettext message to be extracted. In the following case the TRANSLATORS: comment would not have been extracted:
<div id="name">
## TRANSLATORS: This is a proper name. See the gettext
## manual, section Names.
Name: ${_('Francois Pinard')}
</div>
See the Babel User Guide for more information.