A simple and powerful templating engine.
Project description
RNDR is a simple templating engine that unleashes the full power of Python within templates.
Deriving much inspiration from PHP’s templating system, RNDR aims to exploit Python’s inherent utility for templating in a manner that is simple, configurable, and requiring little to learn.
Usage
Syntax
RNDR’s syntax is easy to learn as it involves little more than enclosing a single-line Python statement within a pair of tags.
These tags, the start-tag and the end-tag, are by default @R and R@ respectively.
>>> r = RNDR( ... "<xml>" ... "@R echo( 1 + 1 ) R@" ... "</xml>" ... ) >>> r.render() '<xml>2</xml>'
The output function echo is used in-place of Python’s print as the latter appends a new line, which may or may not be desirable.
Rather than calling the echo function one may also use the output tag: a start tag appended, by default, with an equal sign:
>>> r = RNDR( ... "<xml>" ... "@R= 1 + 1 R@" ... "</xml>" ... ) >>> r.render() '<xml>2</xml>'
The Python language groups the statement blocks of control structures through the use of indentation. Unfortunately, using indentation as a means for managing control-structures within templates is restrictive, fragile, and generally unpleasant.
In its place RNDR allows control structures to be explicitly terminated by providing a control-structure termination statement: end<control-structure>.
>>> r = RNDR( ... "<html>" ... " Hello" ... "@R if 1+1 is 2: R@" ... " World! " ... "@R endif R@" ... "</html>" ... ) >>> print( r.render() ) <html> Hello World! </html>
The syntax described so far is akin to (and drew its inspiration from) the PHP templating engine.
Much like the PHP templating engine, there is no esoteric or neutered templating language to learn: RNDR simply executes Python code placed within statement tags.
>>> r = RNDR( ... "<html>" ... "@R for i in [1,2,3]: R@" ... "@R= i R@ " ... "@R endfor R@" ... "</html>" ... ) >>> print( r.render() ) <html>1 2 3 </html>
>>> r = RNDR( ... "<html>" ... "@R i = 0 R@" ... "@R while True: R@" ... "@R i += 1 R@" ... "@R if i == 3: R@" ... " I'm finally three! " ... "@R break R@" ... "@R endif R@" ... "@R endwhile R@" ... "</html>" ... ) >>> print( r.render() ) <html> I'm finally three! </html>
One can take this to great extremes:
>>> r = RNDR( ... "<html>" ... "@R try: R@" ... "@R 1/0 R@" ... "@R except Exception as e: R@" ... " @R= e R@ is fun! " ... "@R endtry R@" ... "</html>" ... ) >>> print( r.render() ) <html> integer division or modulo by zero is fun! </html>
With respect to the principle of concern separation, seldom could such practice be considered a good idea. Ideally, complex or sensitive functionality should be contained in a domain removed from presentation; logic delegated to the template should be the simplest kind able to perform the given task.
Templates and Context
RNDR accepts templates in the form of Python strings ( both bytestrings and unicode ), and file objects.
>>> f = open('test.rndr.xml','w')
>>> r = f.write(
... "<xml>"
... "@R= 1+1 R@"
... "</xml>"
... )
>>> f.close()
>>> r = RNDR( open('test.rndr.xml') )
>>> r.render()
'<xml>2</xml>'
RNDR also accepts context variables: the variables that will provide the namespace for statements found in the template.
>>> r = RNDR(
... "<xml>"
... "@R= my_var R@"
... "</xml>"
... )
>>> r.render( {'my_var': 'Hello'} )
'<xml>Hello</xml>'
These context variables may be of any type.
>>> r = RNDR(
... "<xml>"
... "@R= my_func('Moe') R@"
... "</xml>"
... )
>>> r.render( {'my_func': lambda x: "Hello " + x } )
'<xml>Hello Moe</xml>'
File and Template Inclusion
RNDR also supports the inclusion of files and other RNDR templates into a template. The content of a file inclusion statement takes the form:
<include_tag_suffix> "filename" | filename_variable
The include_tag_suffix is the tag leading the start_tag of a statement. By default, the include_tag_suffix is an opening angle bracket (‘<’).
@R< "filename" R@ @R< filename_variable R@
Templates included into other templates will share the same context variables.
To provide a complete illustration:
>>> with open('plain.txt','w') as plain, open('renderable.rndr.txt','w') as renderable:
... plain.write(
... " Hello World. "
... )
... renderable.write(
... "@R if name: R@"
... "Hello @R= name R@."
... "@R endif R@"
... )
>>> r = RNDR(
... "<x>"
... "@R< 'plain.txt' R@"
... "@R< 'renderable.rndr.txt' R@"
... "</x>"
... )
>>> print( r.render( context = {'name':'Moe'} ) )
<x> Hello World. Hello Moe.</x>
Django Integration
Some users may want to integrate RNDR into their Django projects. This can be done quite easily: simply insert the line "rndr.loaders.RNDRLoader" into the TEMPLATE_LOADERS list in your projects settings.py file. Note that the RNDR template loader will only load templates that contain the nested/secondary extension ‘.rndr’ (e.g. template.rndr.html ).
TEMPLATE_LOADERS = ( 'rndr.loaders.FileSystemLoader', 'rndr.loaders.AppDirectoriesLoader', ... )
Command-line interface
RNDR also includes a very simple console interface for rendering template in a command-line environment.
There are two positional arguments that may be passed. The first is the path of the template file and the second is the file to which rendered content will be written to.
$ python -m rndr template.rndr.html rendered.html
They default to the standard input and output streams respectively, meaining they can be used in pipes and standard stream redirections.
$ echo "@R if True: R@ Hello @R endfor R@" | python -m rndr Hello $ echo "@R for i in (1,2,3): R@ Hello @R endfor R@" | python -m rndr > rendered.html
One may also provide the context variables for a template by creating a file containing an evaluatable Python dictionary expression ( e.g. {'context_var':123} ) or a JSON array (e.g. { "context_var":123 } ) and providing its file path as the value for the -c or --context arguments.
python -m rndr template.rndr.html rendered.html -c context.py
Finally, one may retrieve the version number by passing the -v and --version arguments, or the help message via -h and --help.
Configuration
RNDR permits the configuration of a few of its features: tags, control structure tracking, and the output function used to print rendered components.
Control-structure tracking
By default, RNDR tracks control structures: every time a control structure is initiated (e.g. if A == B: ) it will be recorded as being active until explicitly terminated (e.g. endif). This allows RNDR to determine exactly what control structures are active or unterminated, and how to manage the indentation of the virtual source built from the statements.
This feature can be disabled. This will result in RNDR being unable to track the particular control structures active, and will require explicit block management through use of the block_start_tag and block_end_tag symbols.
The start of a block is denoted by the block_start symbol, which is found at the end of a statement. The end of a block is denoted by the block_end symbol, which is found at the beginning of a statement. By default, both use the colon (‘:’).
>>> rc = Config( cs_tracking = False ) >>> r = RNDR( ... "<html>" ... " Hello" ... "@R if 1+1 is 3: R@" ... " Fail" ... "@R :else: R@" ... " World! " ... "@R :end R@" ... "</html>", rc ... ) >>> print( r.render() ) <html> Hello World! </html>
This syntax is similar to that of the Templite+ templating engine. Taking advantage of the configurable start_tag and end_tag values, RNDR can fully support a Templite+ template.
>>> templite_config = Config( ... cs_tracking = False, start_tag = '<<', end_tag='>>', ... ) >>> r = RNDR( ... "<html>" ... " Hello" ... "<< if 1+1 is 3: >>" ... " Fail" ... "<< :else: >>" ... " World! " ... "<< :endif >>" ... "</html>", templite_config ... ) >>> print( r.render() ) <html> Hello World! </html>
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