A Mako template is parsed from a text stream containing any kind of content, XML, HTML, email text, etc. The template can further contain Mako-specific directives which represent variable and/or expression substitutions, control structures (i.e. conditionals and loops), server-side comments, full blocks of Python code, as well as various tags that offer additional functionality. All of these constructs compile into real Python code. This means that you can leverage the full power of Python in almost every aspect of a Mako template.
The simplest expression is just a variable substitution. The
syntax for this is the ${}
construct, which is inspired by
Perl, Genshi, JSP EL, and others:
this is x: ${x}
Above, the string representation of x
is applied to the
template’s output stream. If you’re wondering where x
comes
from, it’s usually from the Context
supplied to the
template’s rendering function. If x
was not supplied to the
template and was not otherwise assigned locally, it evaluates to
a special value UNDEFINED
. More on that later.
The contents within the ${}
tag are evaluated by Python
directly, so full expressions are OK:
pythagorean theorem: ${pow(x,2) + pow(y,2)}
The results of the expression are evaluated into a string result in all cases before being rendered to the output stream, such as the above example where the expression produces a numeric result.
Mako includes a number of built-in escaping mechanisms,
including HTML, URI and XML escaping, as well as a “trim”
function. These escapes can be added to an expression
substitution using the |
operator:
${"this is some text" | u}
The above expression applies URL escaping to the expression, and
produces this+is+some+text
. The u
name indicates URL
escaping, whereas h
represents HTML escaping, x
represents XML escaping, and trim
applies a trim function.
Read more about built-in filtering functions, including how to make your own filter functions, in Filtering and Buffering.
A control structure refers to all those things that control the
flow of a program – conditionals (i.e. if
/else
), loops (like
while
and for
), as well as things like try
/except
. In Mako,
control structures are written using the %
marker followed
by a regular Python control expression, and are “closed” by
using another %
marker with the tag “end<name>
”, where
“<name>
” is the keyword of the expression:
% if x==5:
this is some output
% endif
The %
can appear anywhere on the line as long as no text
precedes it; indentation is not significant. The full range of
Python “colon” expressions are allowed here, including
if
/elif
/else
, while
, for
, with
, and even def
,
although Mako has a built-in tag for defs which is more full-featured.
% for a in ['one', 'two', 'three', 'four', 'five']:
% if a[0] == 't':
its two or three
% elif a[0] == 'f':
four/five
% else:
one
% endif
% endfor
The %
sign can also be “escaped”, if you actually want to
emit a percent sign as the first non whitespace character on a
line, by escaping it as in %%
:
%% some text
%% some more text
The loop context provides additional information about a loop
while inside of a % for
structure:
<ul>
% for a in ("one", "two", "three"):
<li>Item ${loop.index}: ${a}</li>
% endfor
</ul>
See The Loop Context for more information on this feature.
New in version 0.7.
The backslash (”\
”) character, placed at the end of any
line, will consume the newline character before continuing to
the next line:
here is a line that goes onto \
another line.
The above text evaluates to:
here is a line that goes onto another line.
Any arbitrary block of python can be dropped in using the <%
%>
tags:
this is a template
<%
x = db.get_resource('foo')
y = [z.element for z in x if x.frobnizzle==5]
%>
% for elem in y:
element: ${elem}
% endfor
Within <% %>
, you’re writing a regular block of Python code.
While the code can appear with an arbitrary level of preceding
whitespace, it has to be consistently formatted with itself.
Mako’s compiler will adjust the block of Python to be consistent
with the surrounding generated Python code.
A variant on <% %>
is the module-level code block, denoted
by <%! %>
. Code within these tags is executed at the module
level of the template, and not within the rendering function of
the template. Therefore, this code does not have access to the
template’s context and is only executed when the template is
loaded into memory (which can be only once per application, or
more, depending on the runtime environment). Use the <%! %>
tags to declare your template’s imports, as well as any
pure-Python functions you might want to declare:
<%!
import mylib
import re
def filter(text):
return re.sub(r'^@', '', text)
%>
Any number of <%! %>
blocks can be declared anywhere in a
template; they will be rendered in the resulting module
in a single contiguous block above all render callables,
in the order in which they appear in the source template.
The rest of what Mako offers takes place in the form of tags.
All tags use the same syntax, which is similar to an XML tag
except that the first character of the tag name is a %
character. The tag is closed either by a contained slash
character, or an explicit closing tag:
<%include file="foo.txt"/>
<%def name="foo" buffered="True">
this is a def
</%def>
All tags have a set of attributes which are defined for each
tag. Some of these attributes are required. Also, many
attributes support evaluation, meaning you can embed an
expression (using ${}
) inside the attribute text:
<%include file="/foo/bar/${myfile}.txt"/>
Whether or not an attribute accepts runtime evaluation depends on the type of tag and how that tag is compiled into the template. The best way to find out if you can stick an expression in is to try it! The lexer will tell you if it’s not valid.
Heres a quick summary of all the tags:
<%page>
¶This tag defines general characteristics of the template, including caching arguments, and optional lists of arguments which the template expects when invoked.
<%page args="x, y, z='default'"/>
Or a page tag that defines caching characteristics:
<%page cached="True" cache_type="memory"/>
Currently, only one <%page>
tag gets used per template, the
rest get ignored. While this will be improved in a future
release, for now make sure you have only one <%page>
tag
defined in your template, else you may not get the results you
want. Further details on what <%page>
is used for are described
in the following sections:
The body() Method - <%page>
is used to define template-level
arguments and defaults
Expression Filtering - expression filters can be applied to all
expressions throughout a template using the <%page>
tag
Caching - options to control template-level caching
may be applied in the <%page>
tag.
<%include>
¶A tag that is familiar from other template languages, %include
is a regular joe that just accepts a file argument and calls in
the rendered result of that file:
<%include file="header.html"/>
hello world
<%include file="footer.html"/>
Include also accepts arguments which are available as <%page>
arguments in the receiving template:
<%include file="toolbar.html" args="current_section='members', username='ed'"/>
<%def>
¶The %def
tag defines a Python function which contains a set
of content, that can be called at some other point in the
template. The basic idea is simple:
<%def name="myfunc(x)">
this is myfunc, x is ${x}
</%def>
${myfunc(7)}
The %def
tag is a lot more powerful than a plain Python def
, as
the Mako compiler provides many extra services with %def
that
you wouldn’t normally have, such as the ability to export defs
as template “methods”, automatic propagation of the current
Context
, buffering/filtering/caching flags, and def calls
with content, which enable packages of defs to be sent as
arguments to other def calls (not as hard as it sounds). Get the
full deal on what %def
can do in Defs and Blocks.
<%block>
¶%block
is a tag that is close to a %def
,
except executes itself immediately in its base-most scope,
and can also be anonymous (i.e. with no name):
<%block filter="h">
some <html> stuff.
</%block>
Inspired by Jinja2 blocks, named blocks offer a syntactically pleasing way to do inheritance:
<html>
<body>
<%block name="header">
<h2><%block name="title"/></h2>
</%block>
${self.body()}
</body>
</html>
Blocks are introduced in Using Blocks and further described in Inheritance.
New in version 0.4.1.
<%namespace>
¶%namespace
is Mako’s equivalent of Python’s import
statement. It allows access to all the rendering functions and
metadata of other template files, plain Python modules, as well
as locally defined “packages” of functions.
<%namespace file="functions.html" import="*"/>
The underlying object generated by %namespace
, an instance of
Namespace
, is a central construct used in
templates to reference template-specific information such as the
current URI, inheritance structures, and other things that are
not as hard as they sound right here. Namespaces are described
in Namespaces.
<%inherit>
¶Inherit allows templates to arrange themselves in inheritance chains. This is a concept familiar in many other template languages.
<%inherit file="base.html"/>
When using the %inherit
tag, control is passed to the topmost
inherited template first, which then decides how to handle
calling areas of content from its inheriting templates. Mako
offers a lot of flexibility in this area, including dynamic
inheritance, content wrapping, and polymorphic method calls.
Check it out in Inheritance.
<%
nsname:
defname>
¶Any user-defined “tag” can be created against
a namespace by using a tag with a name of the form
<%<namespacename>:<defname>>
. The closed and open formats of such a
tag are equivalent to an inline expression and the <%call>
tag, respectively.
<%mynamespace:somedef param="some value">
this is the body
</%mynamespace:somedef>
To create custom tags which accept a body, see Calling a Def with Embedded Content and/or Other Defs.
New in version 0.2.3.
<%call>
¶The call tag is the “classic” form of a user-defined tag, and is
roughly equivalent to the <%namespacename:defname>
syntax
described above. This tag is also described in Calling a Def with Embedded Content and/or Other Defs.
<%doc>
¶The %doc
tag handles multiline comments:
<%doc>
these are comments
more comments
</%doc>
Also the ##
symbol as the first non-space characters on a line can be used for single line comments.
<%text>
¶This tag suspends the Mako lexer’s normal parsing of Mako template directives, and returns its entire body contents as plain text. It is used pretty much to write documentation about Mako:
<%text filter="h">
heres some fake mako ${syntax}
<%def name="x()">${x}</%def>
</%text>
Sometimes you want to stop processing a template or <%def>
method in the middle and just use the text you’ve accumulated so
far. This is accomplished by using return
statement inside
a Python block. It’s a good idea for the return
statement
to return an empty string, which prevents the Python default return
value of None
from being rendered by the template. This
return value is for semantic purposes provided in templates via
the STOP_RENDERING
symbol:
% if not len(records):
No records found.
<% return STOP_RENDERING %>
% endif
Or perhaps:
<%
if not len(records):
return STOP_RENDERING
%>
In older versions of Mako, an empty string can be substituted for
the STOP_RENDERING
symbol:
<% return '' %>
New in version 1.0.2: - added the STOP_RENDERING
symbol which serves
as a semantic identifier for the empty string ""
used by a
Python return
statement.
Comments¶
Comments come in two varieties. The single line comment uses
##
as the first non-space characters on a line:A multiline version exists using
<%doc> ...text... </%doc>
: