Project

General

Profile

Edit History

TemplateParser » History » Version 42

Elmer de Looff, 2012-06-01 13:24
Characters for tags

1 1 Elmer de Looff 
h1. TemplateParser
2 25 Elmer de Looff 





    3
    25
    Elmer de Looff
    
{{>toc}}





    4
    1
    Elmer de Looff
    





    5
    1
    Elmer de Looff
    
The µWeb TemplateParser is a in-house developed templating engine that provides tag replacement, tag-functions and template control functions. This document will describe the following:





    6
    38
    Elmer de Looff
    
* *[[TemplateParser#using|Using TemplateParser]]* inside a µWeb PageMaker





    7
    21
    Elmer de Looff
    
* The *[[TemplateParser#template|Template class]]*, used to parse the templating language





    8
    21
    Elmer de Looff
    
* The *[[TemplateParser#parser|Parser class]]*, which provides template loading and caching





    9
    21
    Elmer de Looff
    
* *[[TemplateParser#syntax|Template syntax]]*, an overview of the language's constructs and behaviors





    10
    1
    Elmer de Looff
    





    11
    1
    Elmer de Looff
    
First though, to help with understanding the TemplateParser, a minimal size template document:





    12
    1
    Elmer de Looff
    





    13
    1
    Elmer de Looff
    
<pre><code class="html">





    14
    1
    Elmer de Looff
    
Hello [title] [name]





    15
    1
    Elmer de Looff
    
</code></pre>





    16
    4
    Elmer de Looff
    





    17
    1
    Elmer de Looff
    
The above document contains two simple template tags. These tags are delimited by square brackets, and they will be replaced by the named argument provided during parsing. If this name is not present, then the literal presentation of the tag will remain in the output.





    18
    1
    Elmer de Looff
    





    19
    38
    Elmer de Looff
    
h1(#using). Using TemplateParser inside µWeb





    20
    38
    Elmer de Looff
    





    21
    38
    Elmer de Looff
    
Within the default µWeb @PageMaker@, there is a @parser@ property, which provides a [[TemplateParser#parser|Parser]] object. The class constant @TEMPLATE_DIR@ provides the template search directory. The default template directory is @'templates'@. *N.B.* This path is relative to the file that contains the PageMaker class.





    22
    38
    Elmer de Looff
    





    23
    38
    Elmer de Looff
    
An example of TemplateParser to create a complete response:





    24
    38
    Elmer de Looff
    
<pre><code class="python">





    25
    38
    Elmer de Looff
    
import uweb





    26
    38
    Elmer de Looff
    
import time





    27
    38
    Elmer de Looff
    





    28
    38
    Elmer de Looff
    
class PageMaker(uweb.PageMaker):





    29
    38
    Elmer de Looff
    
  def VersionPage(self):





    30
    38
    Elmer de Looff
    
    return self.parser.Parse(





    31
    38
    Elmer de Looff
    
      'version.utp', year=time.strftime('%Y'), version=uweb.__version__)





    32
    38
    Elmer de Looff
    
</code></pre>





    33
    38
    Elmer de Looff
    





    34
    38
    Elmer de Looff
    
The example template for the above file could look something like this:





    35
    38
    Elmer de Looff
    





    36
    38
    Elmer de Looff
    
<pre><code class="html">





    37
    38
    Elmer de Looff
    
<!DOCTYPE html>





    38
    38
    Elmer de Looff
    
<html>





    39
    38
    Elmer de Looff
    
  <head>





    40
    38
    Elmer de Looff
    
    <title>µWeb version info</title>





    41
    38
    Elmer de Looff
    
  </head>





    42
    38
    Elmer de Looff
    
  <body>





    43
    38
    Elmer de Looff
    
    <p>µWeb version [version] - Copyright 2010-[year] Underdark</p>





    44
    38
    Elmer de Looff
    
  </body>





    45
    38
    Elmer de Looff
    
</html>





    46
    38
    Elmer de Looff
    
</code></pre>





    47
    38
    Elmer de Looff
    





    48
    38
    Elmer de Looff
    
And would result in the following output:





    49
    38
    Elmer de Looff
    





    50
    38
    Elmer de Looff
    
<pre><code class="html">





    51
    38
    Elmer de Looff
    
<!DOCTYPE html>





    52
    38
    Elmer de Looff
    
<html>





    53
    38
    Elmer de Looff
    
  <head>





    54
    38
    Elmer de Looff
    
    <title>µWeb version info</title>





    55
    38
    Elmer de Looff
    
  </head>





    56
    38
    Elmer de Looff
    
  <body>





    57
    38
    Elmer de Looff
    
    <p>µWeb version 0.12 - Copyright 2010-2012 Underdark</p>





    58
    38
    Elmer de Looff
    
  </body>





    59
    38
    Elmer de Looff
    
</html>





    60
    38
    Elmer de Looff
    
</code></pre>





    61
    38
    Elmer de Looff
    





    62
    38
    Elmer de Looff
    
With these initial small demonstrations behind us, let's explore the @TemplateParser@ further





    63
    38
    Elmer de Looff
    





    64
    5
    Elmer de Looff
    
h1(#template). Template class





    65
    4
    Elmer de Looff
    





    66
    4
    Elmer de Looff
    
The @Template@ class provides the interface for pre-parsing templates, loading them from files and parsing single templates to completion. During pre-parsing, constructs such as loops and conditional statements are converted to @TemplateLoop@ and @TemplateConditional@ objects, and their scopes nested appropriately in the @Template@. Tags are replaced by @TemplateTag@ instances, and text is captured in @TemplateText@. All of these provide @Parse@ methods, which together result in the combined parsed template output.





    67
    4
    Elmer de Looff
    





    68
    4
    Elmer de Looff
    
h2. Creating a template





    69
    4
    Elmer de Looff
    





    70
    4
    Elmer de Looff
    
A template is created simple by providing a string input to the @Template@'s constructor. This will return a valid Template instance (or raise an error if there is a problem with the [[TemplateParser#syntax|syntax]]:





    71
    4
    Elmer de Looff
    





    72
    4
    Elmer de Looff
    
<pre><code class="python">





    73
    21
    Elmer de Looff
    
>>> import templateparser





    74
    4
    Elmer de Looff
    
>>> template = templateparser.Template('Hello [title] [name]')





    75
    4
    Elmer de Looff
    
>>> template





    76
    4
    Elmer de Looff
    
Template([TemplateText('Hello '), TemplateTag('[title]'), TemplateText(' '), TemplateTag('[name]')])





    77
    4
    Elmer de Looff
    
</code></pre>





    78
    4
    Elmer de Looff
    





    79
    4
    Elmer de Looff
    
Above can be seen the various parts of the template, which will be combined to output once parsed.





    80
    4
    Elmer de Looff
    





    81
    4
    Elmer de Looff
    
h2. Loading a template from file





    82
    4
    Elmer de Looff
    





    83
    4
    Elmer de Looff
    
The @Template@ class provides a @classmethod@ called @FromFile@, which loads the template at the path.





    84
    4
    Elmer de Looff
    





    85
    4
    Elmer de Looff
    
Loading a template named @example.utp@ from the current working directory:





    86
    4
    Elmer de Looff
    





    87
    4
    Elmer de Looff
    
<pre><code class="python">





    88
    21
    Elmer de Looff
    
>>> import templateparser





    89
    4
    Elmer de Looff
    
>>> template = templateparser.Template.FromFile('example.utp')





    90
    4
    Elmer de Looff
    
>>> template





    91
    4
    Elmer de Looff
    
Template([TemplateText('Hello '), TemplateTag('[title]'), TemplateText(' '), TemplateTag('[name]')])





    92
    4
    Elmer de Looff
    
</code></pre>





    93
    4
    Elmer de Looff
    





    94
    5
    Elmer de Looff
    
h2. Parsing a template





    95
    4
    Elmer de Looff
    





    96
    4
    Elmer de Looff
    
Parsing a template can be done by calling the @Template@'s @Parse@ method. The keyword arguments provided to this call will from the replacement mapping for the template. In the following example, we will provide one such keyword, and leave the other undefined to show the (basic) behavior of the @Template.Parse@ method.





    97
    4
    Elmer de Looff
    





    98
    4
    Elmer de Looff
    
<pre><code class="python">





    99
    21
    Elmer de Looff
    
>>> import templateparser





    100
    4
    Elmer de Looff
    
>>> template = templateparser.Template('Hello [title] [name]')





    101
    8
    Elmer de Looff
    
>>> template.Parse(title='sir')





    102
    8
    Elmer de Looff
    
'Hello sir [name]'





    103
    4
    Elmer de Looff
    
</code></pre>





    104
    1
    Elmer de Looff
    





    105
    1
    Elmer de Looff
    
h1(#parser). Parser class





    106
    6
    Elmer de Looff
    





    107
    1
    Elmer de Looff
    
The @Parser@ class provides simple management of multiple @Template@ objects. It is mainly used to load templates from disk. When initiating a @Parser@, the first argument provides the search path from where templates should be loaded (the default is the current working directory). An optional second argument can be provided to preload the template cache: a mapping of names and @Template@ objects.





    108
    1
    Elmer de Looff
    





    109
    8
    Elmer de Looff
    
h2. Loading templates





    110
    8
    Elmer de Looff
    





    111
    6
    Elmer de Looff
    
Creating a parser object, and loading the 'example.utp' template from the 'templates' directory works like this:





    112
    6
    Elmer de Looff
    





    113
    6
    Elmer de Looff
    
<pre><code class="python">





    114
    21
    Elmer de Looff
    
>>> import templateparser





    115
    7
    Elmer de Looff
    
>>> # This sets the 'templates' directory as the search path for AddTemplate





    116
    7
    Elmer de Looff
    
>>> parser = templateparser.Parser('templates')





    117
    7
    Elmer de Looff
    
>>> # Loads the 'templates/example.utp' and stores it as 'example.utp':





    118
    26
    Elmer de Looff
    
>>> parser.AddTemplate('example.utp')





    119
    27
    Elmer de Looff
    
>>> parser.Parse('example.utp', title='mister', name='Bob Dobalina')





    120
    1
    Elmer de Looff
    
'Hello mister Bob Dobalina'





    121
    6
    Elmer de Looff
    
</code></pre>





    122
    1
    Elmer de Looff
    





    123
    29
    Elmer de Looff
    
The @AddTemplate@ method takes a second optional argument, which allows us to give the template a different name in the cache:





    124
    29
    Elmer de Looff
    





    125
    29
    Elmer de Looff
    
<pre><code class="python">





    126
    29
    Elmer de Looff
    
>>> parser = templateparser.Parser('templates')





    127
    30
    Elmer de Looff
    
>>> parser.AddTemplate('example.utp', name='greeting')





    128
    29
    Elmer de Looff
    
>>> parser.Parse('greeting', title='mister', name='Bob Dobalina')





    129
    29
    Elmer de Looff
    
'Hello mister Bob Dobalina'





    130
    29
    Elmer de Looff
    
</code></pre>





    131
    29
    Elmer de Looff
    





    132
    29
    Elmer de Looff
    
As you can see, the name of the template in the cache is not necessarily the same as the one on disk. Often though, this is not necessary to change, so @AddTemplate@ need only be called with one argument. Or not at all, as the following section will show.





    133
    1
    Elmer de Looff
    





    134
    8
    Elmer de Looff
    
h2. Template cache and auto-loading





    135
    8
    Elmer de Looff
    





    136
    8
    Elmer de Looff
    
The @Parser@ object behaves like a slightly modified dictionary to achieve this. Retrieving keys yields the associated template. Keys that are not present in the cache are _automatically_ retrieved from the filesystem:





    137
    8
    Elmer de Looff
    





    138
    1
    Elmer de Looff
    
<pre><code class="python">





    139
    8
    Elmer de Looff
    
>>> import templateparser





    140
    8
    Elmer de Looff
    
>>> parser = templateparser.Parser('templates')





    141
    8
    Elmer de Looff
    
>>> 'example.utp' in parser





    142
    6
    Elmer de Looff
    
False       # Since we haven't loaded it, the template it not in the parser





    143
    1
    Elmer de Looff
    
>>> parser





    144
    10
    Elmer de Looff
    
Parser({})  # The parser is empty (has no cached templates)





    145
    10
    Elmer de Looff
    
</code></pre>





    146
    10
    Elmer de Looff
    





    147
    10
    Elmer de Looff
    
Attempting to parse a template that doesn't exist in the parser cache triggers an automatic load:





    148
    10
    Elmer de Looff
    





    149
    31
    Jan Klopper
    
<pre><code class="python">





    150
    10
    Elmer de Looff
    
>>> parser['example.utp'].Parse(title='mister', name='Bob Dobalina')





    151
    10
    Elmer de Looff
    
'Hello mister Bob Dobalina'





    152
    10
    Elmer de Looff
    
>>> 'example.utp' in parser





    153
    10
    Elmer de Looff
    
True





    154
    10
    Elmer de Looff
    
>>> parser





    155
    10
    Elmer de Looff
    
Parser({'example.utp': Template([TemplateText('Hello '), TemplateTag('[title]'),





    156
    10
    Elmer de Looff
    
                                 TemplateText(' '), TemplateTag('[name]')])})





    157
    10
    Elmer de Looff
    
</code></pre>





    158
    10
    Elmer de Looff
    





    159
    10
    Elmer de Looff
    
If these cannot be found, @TemplateReadError@ is raised:





    160
    10
    Elmer de Looff
    





    161
    10
    Elmer de Looff
    
<pre><code class="python">





    162
    10
    Elmer de Looff
    
>>> import templateparser





    163
    10
    Elmer de Looff
    
>>> parser = templateparser.Parser('templates')





    164
    10
    Elmer de Looff
    
>>> parser['bad_template.utp'].Parse(failure='imminent')





    165
    10
    Elmer de Looff
    
Traceback (most recent call last):





    166
    10
    Elmer de Looff
    
  File "<stdin>", line 1, in <module>





    167
    1
    Elmer de Looff
    
  File "/var/lib/underdark/libs/uweb/templateparser.py", line 147, in __getitem__





    168
    37
    Elmer de Looff
    
    self.AddTemplate(template)





    169
    37
    Elmer de Looff
    
  File "/var/lib/underdark/libs/uweb/templateparser.py", line 171, in AddTemplate





    170
    37
    Elmer de Looff
    
    raise TemplateReadError('Could not load template %r' % template_path)





    171
    37
    Elmer de Looff
    
underdark.libs.uweb.templateparser.TemplateReadError: Could not load template 'templates/bad_template.utp'





    172
    37
    Elmer de Looff
    
</code></pre>





    173
    37
    Elmer de Looff
    





    174
    37
    Elmer de Looff
    
h2. @Parse@ and @ParseString@ methods





    175
    37
    Elmer de Looff
    





    176
    37
    Elmer de Looff
    
For convencience and consistency, the @Parser@ comes with two handy methods to provide parsing of @Template@ objects, one from its cache, one from raw template strings. It is recommended to use these over the previously shown direct key-based access:





    177
    37
    Elmer de Looff
    





    178
    37
    Elmer de Looff
    
<pre><code class="python">





    179
    37
    Elmer de Looff
    
>>> import templateparser





    180
    37
    Elmer de Looff
    
>>> parser = templateparser.Parser('templates')





    181
    37
    Elmer de Looff
    
>>> parser.Parse('example.utp', title='mister', name='Bob Dobalina')





    182
    10
    Elmer de Looff
    
'Hello mister Bob Dobalina'





    183
    10
    Elmer de Looff
    
>>> parser.ParseString('Hello [title] [name]', title='mister', name='Bob Dobalina')





    184
    10
    Elmer de Looff
    
'Hello mister Bob Dobalina'</code></pre>





    185
    1
    Elmer de Looff
    





    186
    5
    Elmer de Looff
    
h1(#syntax). Templating language syntax





    187
    11
    Elmer de Looff
    





    188
    11
    Elmer de Looff
    
The templating syntax is relatively limited, but with the limited syntax it provides a flexible and rich system to create templates. Covered in these examples are:





    189
    11
    Elmer de Looff
    
* Simple tags (used in various examples above)





    190
    11
    Elmer de Looff
    
* Tag indexing





    191
    11
    Elmer de Looff
    
* Tag functions





    192
    11
    Elmer de Looff
    
* Template language constructs





    193
    11
    Elmer de Looff
    





    194
    11
    Elmer de Looff
    
All examples will consist of three parts:





    195
    11
    Elmer de Looff
    
# The example template





    196
    11
    Elmer de Looff
    
# The python invocation string (the template will be named 'example.utp')





    197
    11
    Elmer de Looff
    
# The resulting output (as source, not as parsed HTML)





    198
    11
    Elmer de Looff
    





    199
    11
    Elmer de Looff
    
h2. Simple tags





    200
    11
    Elmer de Looff
    





    201
    11
    Elmer de Looff
    
This is an example for the most basic form of template tags. The tag is enclosed by square brackets as such: @[tag]@. Tags that match a provided argument to the Parse call get replaced. If there is no argument that matches the tag name, it is returned in the output verbatim. This is also demonstrated in the below example





    202
    11
    Elmer de Looff
    





    203
    11
    Elmer de Looff
    
The example below is a repeat of the example how to use TemplateParser inside µWeb, and shows the template result:





    204
    11
    Elmer de Looff
    





    205
    11
    Elmer de Looff
    
<pre><code class="html">





    206
    11
    Elmer de Looff
    
<!DOCTYPE html>





    207
    11
    Elmer de Looff
    
<html>





    208
    11
    Elmer de Looff
    
  <head>





    209
    11
    Elmer de Looff
    
    <title>µWeb version info</title>





    210
    11
    Elmer de Looff
    
  </head>





    211
    11
    Elmer de Looff
    
  <body>





    212
    11
    Elmer de Looff
    
    <p>µWeb version [version] - Copyright 2010-[year] Underdark</p>





    213
    11
    Elmer de Looff
    
    <p>





    214
    11
    Elmer de Looff
    
      This [paragraph] is not replaced because there is no





    215
    11
    Elmer de Looff
    
      paragraph argument provided to the parser.





    216
    11
    Elmer de Looff
    
    </p>





    217
    11
    Elmer de Looff
    
  </body>





    218
    11
    Elmer de Looff
    
</html>





    219
    11
    Elmer de Looff
    
</code></pre>





    220
    11
    Elmer de Looff
    





    221
    11
    Elmer de Looff
    
<pre><code class="python">





    222
    11
    Elmer de Looff
    
>>> parser.Parse('version.utp', year=time.strftime('%Y'), version=uweb.__version__)





    223
    11
    Elmer de Looff
    
</code></pre>





    224
    11
    Elmer de Looff
    





    225
    11
    Elmer de Looff
    
<pre><code class="html">





    226
    11
    Elmer de Looff
    
<!DOCTYPE html>





    227
    11
    Elmer de Looff
    
<html>





    228
    11
    Elmer de Looff
    
  <head>





    229
    11
    Elmer de Looff
    
    <title>µWeb version info</title>





    230
    11
    Elmer de Looff
    
  </head>





    231
    11
    Elmer de Looff
    
  <body>





    232
    11
    Elmer de Looff
    
    <p>µWeb version 0.11 - Copyright 2010-212 Underdark</p>





    233
    11
    Elmer de Looff
    
    <p>





    234
    11
    Elmer de Looff
    
      This [paragraph] is not replaced because there is no





    235
    11
    Elmer de Looff
    
      paragraph argument provided to the parser.





    236
    11
    Elmer de Looff
    
    </p>





    237
    11
    Elmer de Looff
    
  </body>





    238
    11
    Elmer de Looff
    
</html>





    239
    11
    Elmer de Looff
    
</code></pre>





    240
    11
    Elmer de Looff
    





    241
    42
    Elmer de Looff
    
h3. Tag characters





    242
    42
    Elmer de Looff
    





    243
    42
    Elmer de Looff
    
Tag names are created from the same characters as valid Python variable names. This means they can contain upper and lower case letters, numbers and underscores. In regex terms, a tag should match @\w+@.





    244
    42
    Elmer de Looff
    





    245
    42
    Elmer de Looff
    
*N.B.:* Some names are illegal in Python as variable names but valid as tag names (tag names may start with a number). You can use these and pass the replacements as a dictionary using ** if you have a need for it.





    246
    42
    Elmer de Looff
    





    247
    11
    Elmer de Looff
    
h2. Tag indexing





    248
    11
    Elmer de Looff
    





    249
    32
    Elmer de Looff
    
In addition to simple (re)placement of strings using the @TemplateParser@, you can also provide it with a @list@, @dictionary@, or other indexable object, and from it, fetch various @indices@, @keys@ or @attributes@. The separation character between the _tagname_ and the _index_ is the _colon_ (":"):





    250
    32
    Elmer de Looff
    





    251
    32
    Elmer de Looff
    





    252
    32
    Elmer de Looff
    
h3. List/tuple index addressing





    253
    32
    Elmer de Looff
    





    254
    34
    Elmer de Looff
    
This works for lists and tuples, but also for any other object that supports indexing. That is, every object that accepts integers on its @__getitem__@ method.





    255
    34
    Elmer de Looff
    





    256
    32
    Elmer de Looff
    
<pre><code class="html">





    257
    32
    Elmer de Looff
    
This is [var:0] [var:1].





    258
    32
    Elmer de Looff
    
</code></pre>





    259
    32
    Elmer de Looff
    





    260
    32
    Elmer de Looff
    
<pre><code class="python">





    261
    32
    Elmer de Looff
    
>>> parser.Parse('message.utp', var=('delicious', 'spam'))





    262
    32
    Elmer de Looff
    
</code></pre>





    263
    32
    Elmer de Looff
    





    264
    32
    Elmer de Looff
    
<pre><code class="html">





    265
    32
    Elmer de Looff
    
This is delicious spam.





    266
    32
    Elmer de Looff
    
</code></pre>





    267
    32
    Elmer de Looff
    





    268
    33
    Elmer de Looff
    
h3. Dictionary key addressing





    269
    32
    Elmer de Looff
    





    270
    34
    Elmer de Looff
    
This works for dictionaries, but also for any other object that behaves like a key-value mapping. That is, every object that accepts strings on its @__getitem__@ method.





    271
    34
    Elmer de Looff
    





    272
    32
    Elmer de Looff
    
<pre><code class="html">





    273
    32
    Elmer de Looff
    
This is [var:adjective] [var:noun].





    274
    32
    Elmer de Looff
    
</code></pre>





    275
    32
    Elmer de Looff
    





    276
    32
    Elmer de Looff
    
<pre><code class="python">





    277
    32
    Elmer de Looff
    
>>> parser.Parse('message.utp', var={'adjective': 'delicious', 'noun': 'spam'})





    278
    32
    Elmer de Looff
    
</code></pre>





    279
    32
    Elmer de Looff
    





    280
    32
    Elmer de Looff
    
<pre><code class="html">





    281
    32
    Elmer de Looff
    
This is delicious spam.





    282
    32
    Elmer de Looff
    
</code></pre>





    283
    32
    Elmer de Looff
    





    284
    33
    Elmer de Looff
    
h3. Attribute name addressing





    285
    32
    Elmer de Looff
    





    286
    34
    Elmer de Looff
    
This works for any object that has named attributes. If the attribute is a method, it will *not* be executed automatically, the return value will simply be the (un)bound method itself.





    287
    34
    Elmer de Looff
    





    288
    32
    Elmer de Looff
    
<pre><code class="html">





    289
    32
    Elmer de Looff
    
This is [var:adjective] [var:noun].





    290
    32
    Elmer de Looff
    
</code></pre>





    291
    32
    Elmer de Looff
    





    292
    32
    Elmer de Looff
    
<pre><code class="python">





    293
    32
    Elmer de Looff
    
>>> class Struct(object):





    294
    32
    Elmer de Looff
    
...   pass





    295
    32
    Elmer de Looff
    
...





    296
    32
    Elmer de Looff
    
>>> var = Struct()





    297
    32
    Elmer de Looff
    
>>> var.adjective = 'delicious'





    298
    32
    Elmer de Looff
    
>>> var.noun = 'spam'





    299
    32
    Elmer de Looff
    
>>> parser.Parse('message.utp', var=var)





    300
    32
    Elmer de Looff
    
</code></pre>





    301
    32
    Elmer de Looff
    





    302
    32
    Elmer de Looff
    
<pre><code class="html">





    303
    32
    Elmer de Looff
    
This is delicious spam.





    304
    32
    Elmer de Looff
    
</code></pre>





    305
    32
    Elmer de Looff
    





    306
    33
    Elmer de Looff
    
h3. Lookup order





    307
    32
    Elmer de Looff
    





    308
    32
    Elmer de Looff
    
For objects and constructs that provide multiple ways of looking up information, the lookup order can be very important. For any of the first three steps, if they are successful, the retrieved value is returned, and no further attempts are made:





    309
    32
    Elmer de Looff
    





    310
    32
    Elmer de Looff
    
# If the @needle@ is parseable as integer, it will first be used as an index. This will also work for mappings with numeric keys;





    311
    32
    Elmer de Looff
    
# If the above fails, the @needle@ is assumed to be a string-like mapping key, and this is attempted





    312
    32
    Elmer de Looff
    
# If the above fails, the @needle@ is used as an attribute name;





    313
    32
    Elmer de Looff
    
# If all of the above fail, *@TemplateKeyError@* is raised, as the @needle@ could not be found on the object.





    314
    34
    Elmer de Looff
    





    315
    34
    Elmer de Looff
    
h3. Nested indexes





    316
    34
    Elmer de Looff
    





    317
    34
    Elmer de Looff
    
There may be cases where the value you need is not at the top-level index of an object. This is not a problem, since TemplateParser supports arbitrary-depth nested structures in its index-lookup:





    318
    34
    Elmer de Looff
    





    319
    34
    Elmer de Looff
    
<pre><code class="html">





    320
    34
    Elmer de Looff
    
This is a variable from [some:levels:down:1].





    321
    34
    Elmer de Looff
    
</code></pre>





    322
    34
    Elmer de Looff
    





    323
    34
    Elmer de Looff
    
<pre><code class="python">





    324
    34
    Elmer de Looff
    
>>> class Struct(object):





    325
    34
    Elmer de Looff
    
...   pass





    326
    34
    Elmer de Looff
    
...





    327
    34
    Elmer de Looff
    
>>> var = Struct()





    328
    34
    Elmer de Looff
    
>>> var.levels = {'down': ('the sky', 'the depths')}





    329
    34
    Elmer de Looff
    
>>> parser.Parse('message.utp', some=var)





    330
    34
    Elmer de Looff
    
</code></pre>





    331
    34
    Elmer de Looff
    





    332
    34
    Elmer de Looff
    
<pre><code class="html">





    333
    34
    Elmer de Looff
    
This is a variable from the depths.





    334
    34
    Elmer de Looff
    
</code></pre>





    335
    16
    Elmer de Looff
    





    336
    11
    Elmer de Looff
    
h2. Tag functions





    337
    11
    Elmer de Looff
    





    338
    35
    Elmer de Looff
    
Once you arrive at the tag/value you want, there's often some things that need to happen before the resulting template is sent to the requesting client (browser). HTML escaping is an obvious one, but url quoting of single arguments may also be helpful, as well as uppercasing, printing the length of a list (instead of the raw list) and various other uses.





    339
    15
    Elmer de Looff
    





    340
    21
    Elmer de Looff
    
h3. Default html escaping





    341
    1
    Elmer de Looff
    





    342
    36
    Elmer de Looff
    
Using a tag function is a fairly straightforward process, just add the name of the function after the tagname, separated by a pipe ( | ):





    343
    35
    Elmer de Looff
    





    344
    36
    Elmer de Looff
    
<pre><code class="html">





    345
    36
    Elmer de Looff
    
And he said: [message|html]





    346
    36
    Elmer de Looff
    
</code></pre>





    347
    36
    Elmer de Looff
    





    348
    36
    Elmer de Looff
    
<pre><code class="python">





    349
    36
    Elmer de Looff
    
>>> parser.Parse('message.utp', message='"Hello"')





    350
    36
    Elmer de Looff
    
</code></pre>





    351
    36
    Elmer de Looff
    





    352
    36
    Elmer de Looff
    
<pre><code class="html">





    353
    36
    Elmer de Looff
    
And he said: &quot;Hello&quot;





    354
    36
    Elmer de Looff
    
</code></pre>





    355
    36
    Elmer de Looff
    





    356
    39
    Elmer de Looff
    
Using the *html* tag function makes the tag value safe for printing in an HTML document. Because we believe this is _really_ important, the html escaping tag function is always applied when no other tag function is applied:





    357
    36
    Elmer de Looff
    





    358
    36
    Elmer de Looff
    
<pre><code class="html">





    359
    36
    Elmer de Looff
    
And he said: [message]





    360
    36
    Elmer de Looff
    
</code></pre>





    361
    36
    Elmer de Looff
    





    362
    36
    Elmer de Looff
    
<pre><code class="python">





    363
    36
    Elmer de Looff
    
>>> parser.Parse('message.utp', message='"Hello"')





    364
    36
    Elmer de Looff
    
</code></pre>





    365
    36
    Elmer de Looff
    





    366
    36
    Elmer de Looff
    
<pre><code class="html">





    367
    36
    Elmer de Looff
    
And he said: &quot;Hello&quot;





    368
    36
    Elmer de Looff
    
</code></pre>





    369
    36
    Elmer de Looff
    





    370
    36
    Elmer de Looff
    
Only when you use another tag function, or specifically tell @TemplateParser@ to push the _raw_ tag value into the output, are the quotes allowed through unchanged:





    371
    36
    Elmer de Looff
    





    372
    36
    Elmer de Looff
    
<pre><code class="html">





    373
    36
    Elmer de Looff
    
And he said: [message|raw]





    374
    36
    Elmer de Looff
    
</code></pre>





    375
    36
    Elmer de Looff
    





    376
    36
    Elmer de Looff
    
<pre><code class="python">





    377
    36
    Elmer de Looff
    
>>> parser.Parse('message.utp', message='"Hello"')





    378
    36
    Elmer de Looff
    
</code></pre>





    379
    36
    Elmer de Looff
    





    380
    36
    Elmer de Looff
    
<pre><code class="html">





    381
    36
    Elmer de Looff
    
And he said: "Hello"





    382
    36
    Elmer de Looff
    
</code></pre>





    383
    36
    Elmer de Looff
    





    384
    35
    Elmer de Looff
    
h3. Predefined tag functions





    385
    1
    Elmer de Looff
    





    386
    36
    Elmer de Looff
    
* *html* &ndash; This tag function escapes content to be safe for inclusion in HTML pages. This means that the ampersand ( & ), single and double quotes ( '  &nbsp;and&nbsp; " ) and the pointy brackets ( < &nbsp;and&nbsp; > ) are converted to their respective "character entity references":http://en.wikipedia.org/wiki/Character_entity_reference





    387
    1
    Elmer de Looff
    
* _default_ &ndash; This is the tag function that will be executed when no other tag functions have been specified for a tag. By default, this will do the same as the *html* tag function. This can be adjusted by assigning another tag function to this name.





    388
    35
    Elmer de Looff
    
* *raw* &ndash; This tag function passes the tag through without change. This is the function to use when you have no tag function to apply, but do not want the tag to be HTML-escaped.





    389
    36
    Elmer de Looff
    
* *url* &ndash; This tag function prepares the tag for use in URLs. Space are converted to plus-signs ( + ), and other characters that are considered unsafe for URLs are converted to "percent-notation":http://en.wikipedia.org/wiki/Percent-encoding.





    390
    1
    Elmer de Looff
    





    391
    35
    Elmer de Looff
    
h3. Adding custom functions





    392
    35
    Elmer de Looff
    





    393
    35
    Elmer de Looff
    
Custom methods can be added to a @Parser@ object using the method @RegisterFunction@. This takes a name, and a single-argument function. When this function is encountered in a tag, it will be given the current tag value, and its result will be output to the template, or passed into the next function:





    394
    35
    Elmer de Looff
    





    395
    35
    Elmer de Looff
    
<pre><code class="python">





    396
    35
    Elmer de Looff
    
>>> from uweb import templateparser





    397
    35
    Elmer de Looff
    
>>> parser = templateparser.Parser()





    398
    35
    Elmer de Looff
    
>>> parser.RegisterFunction('len', len)





    399
    35
    Elmer de Looff
    
>>> template = 'The number of people in this group: [people|len].'





    400
    35
    Elmer de Looff
    
>>> parser.ParseString(template, elements=['Eric', 'Michael', 'John', 'Terry'])





    401
    35
    Elmer de Looff
    
'The number of people in this group: 4.'





    402
    35
    Elmer de Looff
    
</code></pre>





    403
    35
    Elmer de Looff
    





    404
    40
    Elmer de Looff
    
*N.B.:* Using custom functions (or in fact any function other than _html_ or no function) will suppress HTML escaping. If your content is still user-driven, or not otherwise made safe for output, *it is strongly recommended you apply html escaping*. This can be achieved by chaining functions, as explained below.





    405
    40
    Elmer de Looff
    





    406
    41
    Elmer de Looff
    
h3. Function chaining





    407
    35
    Elmer de Looff
    





    408
    35
    Elmer de Looff
    
Multiple function calls can be chained after one another. The functions are processed left to right, and the result of each function is passed into the next, without any intermediate editing or changes:





    409
    35
    Elmer de Looff
    





    410
    35
    Elmer de Looff
    
Setting up the parser and registering our tag function





    411
    35
    Elmer de Looff
    
<pre><code class="python">





    412
    35
    Elmer de Looff
    
>>> from uweb import templateparser





    413
    35
    Elmer de Looff
    
>>> parser = templateparser.Parser()





    414
    35
    Elmer de Looff
    
>>> parser.RegisterFunction('first', lambda x: x[0])





    415
    35
    Elmer de Looff
    
</code></pre>





    416
    35
    Elmer de Looff
    





    417
    35
    Elmer de Looff
    
Working just one tag function returns the first element from the list:





    418
    35
    Elmer de Looff
    
<pre><code class="python">





    419
    35
    Elmer de Looff
    
>>> template = 'The first element of list: [elements|first].'





    420
    35
    Elmer de Looff
    
>>> parser.ParseString(template, elements=['Eric', 'Michael', 'John', 'Terry'])





    421
    35
    Elmer de Looff
    
'The first element of list: Eric.'





    422
    35
    Elmer de Looff
    
</code></pre>





    423
    35
    Elmer de Looff
    





    424
    35
    Elmer de Looff
    
Repeating the function on the string returns the first character from that string:





    425
    35
    Elmer de Looff
    
<pre><code class="python">





    426
    35
    Elmer de Looff
    
>>> template = 'The first element of the first element of list: [elements|first|first].'





    427
    35
    Elmer de Looff
    
>>> parser.ParseString(template, elements=['Eric', 'Michael', 'John', 'Terry'])





    428
    35
    Elmer de Looff
    
'The first element of the first element of list: E.'





    429
    35
    Elmer de Looff
    
</code></pre>





    430
    11
    Elmer de Looff
    





    431
    23
    Elmer de Looff
    
h2. TemplateLoop





    432
    11
    Elmer de Looff
    





    433
    23
    Elmer de Looff
    
As a language construct, TemplateParser has an understanding of iteration. The @TemplateLoop@ can be compared to the Python @for@-loop, or the @foreach@ construct in other languages (lazy iteration over the values of an iterable).





    434
    1
    Elmer de Looff
    





    435
    23
    Elmer de Looff
    
h3. Syntax and properties





    436
    23
    Elmer de Looff
    





    437
    23
    Elmer de Looff
    
*Syntax: @{{ for local_var in [collection] }}@*





    438
    20
    Elmer de Looff
    
* The double accolades (curly braces) indicate the beginning and end of the construct;





    439
    20
    Elmer de Looff
    
* The @for@ keyword indicates the structure to execute;





    440
    20
    Elmer de Looff
    
* @local_var@ is the name which references the loop variable;





    441
    20
    Elmer de Looff
    
* @[collection]@ is the tag that provides the iteratable.





    442
    20
    Elmer de Looff
    





    443
    20
    Elmer de Looff
    
*Properties*





    444
    20
    Elmer de Looff
    
* The local name is stated without brackets (as it's no tag itself)





    445
    1
    Elmer de Looff
    
* When it needs to be placed in the output, the local name should have brackets (like any other tag)





    446
    20
    Elmer de Looff
    
* *N.B.* The local variable does _not_ bleed into the outer scope after the loop has completed.





    447
    20
    Elmer de Looff
    
 It is therefore possible (though not recommended) to name the loop variable after the iterable: @{{ for collection in [collection] }}@.





    448
    20
    Elmer de Looff
    





    449
    23
    Elmer de Looff
    
h3. Example of a @TemplateLoop@





    450
    20
    Elmer de Looff
    





    451
    20
    Elmer de Looff
    
<pre><code class="html">





    452
    20
    Elmer de Looff
    
<html>





    453
    20
    Elmer de Looff
    
  <body>





    454
    20
    Elmer de Looff
    
    <ul>





    455
    20
    Elmer de Looff
    
    {{ for name in [presidents] }}





    456
    20
    Elmer de Looff
    
      <li>President [name]</li>





    457
    20
    Elmer de Looff
    
    {{ endfor }}





    458
    20
    Elmer de Looff
    
    </ul>





    459
    20
    Elmer de Looff
    
  </body>





    460
    20
    Elmer de Looff
    
</html>





    461
    20
    Elmer de Looff
    
</code></pre>





    462
    20
    Elmer de Looff
    





    463
    20
    Elmer de Looff
    
<pre><code class="python">





    464
    20
    Elmer de Looff
    
>>> parser.Parse('rushmore.utp', presidents=['Washington', 'Jefferson', 'Roosevelt', 'Lincoln'])





    465
    20
    Elmer de Looff
    
</code></pre>





    466
    20
    Elmer de Looff
    





    467
    20
    Elmer de Looff
    
<pre><code class="html">





    468
    20
    Elmer de Looff
    
<html>





    469
    20
    Elmer de Looff
    
  <body>





    470
    1
    Elmer de Looff
    
    <ul>





    471
    1
    Elmer de Looff
    
      <li>President Washington</li>





    472
    1
    Elmer de Looff
    
      <li>President Jefferson</li>





    473
    1
    Elmer de Looff
    
      <li>President Roosevelt</li>





    474
    1
    Elmer de Looff
    
      <li>President Lincoln</li>





    475
    1
    Elmer de Looff
    
    </ul>





    476
    1
    Elmer de Looff
    
  </body>





    477
    1
    Elmer de Looff
    
</html>





    478
    1
    Elmer de Looff
    
</code></pre>





    479
    1
    Elmer de Looff
    





    480
    1
    Elmer de Looff
    
h2. Inlining templates





    481
    21
    Elmer de Looff
    





    482
    21
    Elmer de Looff
    
Often, there will be snippets of a template that will see a lot of reuse. Page headers and footers are often the same on many pages, and having several redundant copies means that changes will have to be replicated to each of these occurrances. To reduce the need for this, TemplateParser has an @inline@ statement. Using this you can specify a template that is available in the @[[TemplateParser#Parser]]@ instance and the statement will be replaced by the template.





    483
    21
    Elmer de Looff
    





    484
    21
    Elmer de Looff
    
Of course, if the inlined template is not already in the @Parser@ instance, the autoloading mechanism will trigger, and the named template will be search for in the @Parser@'s template directory.





    485
    21
    Elmer de Looff
    





    486
    21
    Elmer de Looff
    
First, we will define our inline template, @'inline_hello.utp'@:





    487
    21
    Elmer de Looff
    





    488
    21
    Elmer de Looff
    
<pre><code class="html">





    489
    21
    Elmer de Looff
    
<p>Hello [name]</p>





    490
    21
    Elmer de Looff
    
</code></pre>





    491
    21
    Elmer de Looff
    





    492
    21
    Elmer de Looff
    
Secondly, our main template, @'hello.utp'@:





    493
    21
    Elmer de Looff
    





    494
    21
    Elmer de Looff
    
<pre><code class="html">





    495
    21
    Elmer de Looff
    
<h1>Greetings</h1>





    496
    21
    Elmer de Looff
    
{{ inline inline_hello.utp }}





    497
    21
    Elmer de Looff
    
</code></pre>





    498
    21
    Elmer de Looff
    





    499
    21
    Elmer de Looff
    
Then we parse the template:





    500
    21
    Elmer de Looff
    





    501
    21
    Elmer de Looff
    
<pre><code class="python">





    502
    21
    Elmer de Looff
    
>>> parser.Parse('hello.utp', name='Dr John')





    503
    21
    Elmer de Looff
    
</code></pre>





    504
    21
    Elmer de Looff
    





    505
    21
    Elmer de Looff
    
<pre><code class="html">





    506
    21
    Elmer de Looff
    
<h1>Greetings</h1>





    507
    21
    Elmer de Looff
    
<p>Hello Dr John</p>





    508
    21
    Elmer de Looff
    
</code></pre>





    509
    11
    Elmer de Looff
    





    510
    11
    Elmer de Looff
    
h2. Conditional statements





    511
    11
    Elmer de Looff
    





    512
    22
    Elmer de Looff
    
Often, you'll want the output of your template to be dependent on the value, presence, or boolean value of another tag. For instance, we may want a print a list of attendees to a party. We start the @if@ conditional by checking the boolean value of the @attendees@ tag. If this list if not-empty, we will print the attendee names, but if it's empty (or contains only a single entry), we'll tell the user in more intelligent ways than giving them a list with zero entries:





    513
    22
    Elmer de Looff
    





    514
    22
    Elmer de Looff
    
<pre><code class="html">





    515
    22
    Elmer de Looff
    
<h1>Party attendees</h1>





    516
    22
    Elmer de Looff
    
{{ if len([attendees]) > 1 }}





    517
    22
    Elmer de Looff
    
  <ol>





    518
    22
    Elmer de Looff
    
    {{ for attendee in [attendees] }}





    519
    22
    Elmer de Looff
    
    <li>[attendee:name]</li>





    520
    22
    Elmer de Looff
    
    {{ endfor }}





    521
    22
    Elmer de Looff
    
  </ol>





    522
    22
    Elmer de Looff
    
{{ elif [attendees] }}





    523
    22
    Elmer de Looff
    
  <p>only [attendees:0:name] is attending.</p>





    524
    22
    Elmer de Looff
    
{{ else }}





    525
    22
    Elmer de Looff
    
  <p>There are no registered attendees yet.</p>





    526
    22
    Elmer de Looff
    
{{ endif }}





    527
    22
    Elmer de Looff
    
</code></pre>





    528
    22
    Elmer de Looff
    





    529
    22
    Elmer de Looff
    
For the case where there are several attendees:





    530
    22
    Elmer de Looff
    





    531
    22
    Elmer de Looff
    
<pre><code class="python">





    532
    22
    Elmer de Looff
    
>>> parser.Parse('party.utp', attendees=[





    533
    22
    Elmer de Looff
    
...    {'name': 'Livingstone'},





    534
    22
    Elmer de Looff
    
...    {'name': 'Cook'},





    535
    22
    Elmer de Looff
    
...    {'name': 'Drake'}])





    536
    22
    Elmer de Looff
    
</code></pre>





    537
    22
    Elmer de Looff
    





    538
    22
    Elmer de Looff
    
<pre><code class="html">





    539
    22
    Elmer de Looff
    
<h1>Party attendees</h1>





    540
    22
    Elmer de Looff
    
<ol>





    541
    22
    Elmer de Looff
    
  <li>Livingstone</li>





    542
    22
    Elmer de Looff
    
  <li>Cook</li>





    543
    22
    Elmer de Looff
    
  <li>Drake</li>





    544
    22
    Elmer de Looff
    
</ol>





    545
    22
    Elmer de Looff
    
</code></pre>





    546
    22
    Elmer de Looff
    





    547
    22
    Elmer de Looff
    
For the case where there is one attendee:





    548
    22
    Elmer de Looff
    





    549
    22
    Elmer de Looff
    
<pre><code class="python">





    550
    22
    Elmer de Looff
    
>>> parser.Parse('party.utp', attendees=[{'name': 'Johnny'}])





    551
    22
    Elmer de Looff
    
</code></pre>





    552
    22
    Elmer de Looff
    





    553
    22
    Elmer de Looff
    
<pre><code class="html">





    554
    22
    Elmer de Looff
    
<h1>Party attendees</h1>





    555
    22
    Elmer de Looff
    
<p>Only Johnny is attending.</p>





    556
    22
    Elmer de Looff
    
</code></pre>





    557
    22
    Elmer de Looff
    





    558
    22
    Elmer de Looff
    
And in the case where there are no attendees:





    559
    22
    Elmer de Looff
    





    560
    22
    Elmer de Looff
    
<pre><code class="python">





    561
    22
    Elmer de Looff
    
>>> parser.Parse('party.utp', attendees=[])





    562
    22
    Elmer de Looff
    
</code></pre>





    563
    22
    Elmer de Looff
    





    564
    22
    Elmer de Looff
    
<pre><code class="html">





    565
    22
    Elmer de Looff
    
<h1>Party attendees</h1>





    566
    22
    Elmer de Looff
    
<p>There are no registered attendees yet.</p>





    567
    22
    Elmer de Looff
    
</code></pre>





    568
    22
    Elmer de Looff
    





    569
    22
    Elmer de Looff
    
h3. Properties of conditional statements





    570
    22
    Elmer de Looff
    





    571
    22
    Elmer de Looff
    
* *All template keys must be referenced as proper tag*





    572
    22
    Elmer de Looff
    
 This is to prevent mixing of the template variables with the functions and reserved names of Python itself. Conditional expressions are evaluated using @eval()@, and proper tags are replaced by temporary names, the values of which are stored in a retrieve-on-demand dictionary. This makes them perfectly safe with regard to the value of template replacements, but some care should be taken with the writing of the conditional expressions.





    573
    22
    Elmer de Looff
    
* *It is possible to index tags in conditional statements*





    574
    22
    Elmer de Looff
    
 This allows for decisions based on the values in those indexes/keys. For instance, @Person@ objects can be checked for gender, so that the correct gender-based icon can be displayed next to them.





    575
    22
    Elmer de Looff
    
* *Referencing a tag or index that doesn't exist raises @TemplateNameError*





    576
    22
    Elmer de Looff
    
 Unlike in regular template text, there is no suitable fallback value for a tag or index that cannot be retrieved. However, in most cases this can be prevented by making use of the following property:





    577
    22
    Elmer de Looff
    
* *Statement evaluation is lazy*





    578
    22
    Elmer de Looff
    
 Template conditions are processed left to right, and short-circuited where possible. If the first member of an @or@ group succeeds, the return value is already known. Similarly, if the first member of an @and@ group fails, the second part need not be evaluated. This way @TemplateNameErrors@ can often be prevented, as in most cases, presence of indexes can be confirmed before accessing.





    579
    22
    Elmer de Looff
    





    580
    22
    Elmer de Looff
    





    581
    11
    Elmer de Looff
    
h2. Template unicode handling





    582
    11
    Elmer de Looff
    





    583
    11
    Elmer de Looff
    
Any @unicode@ object found while parsing, will automatically be encoded to UTF-8:





    584
    11
    Elmer de Looff
    





    585
    11
    Elmer de Looff
    
<pre><code class="python">





    586
    11
    Elmer de Looff
    
>>> template = 'Underdark [love] [app]'





    587
    11
    Elmer de Looff
    
>>> output = parser.ParseString(template, love=u'\u2665', app=u'\N{micro sign}Web')





    588
    11
    Elmer de Looff
    
>>> output





    589
    12
    Elmer de Looff
    
'Underdark \xe2\x99\xa5 \xc2\xb5Web'  # The output in its raw UTF-8 representation





    590
    11
    Elmer de Looff
    
>>> output.decode('UTF8')





    591
    12
    Elmer de Looff
    
u'Underdark \u2665 \xb5Web'           # The output converted to a Unicode object





    592
    19
    Elmer de Looff
    
>>> print output





    593
    19
    Elmer de Looff
    
Underdark ♥ µWeb                      # And the printed UTF-8 as we desired it.





    594
    14
    Elmer de Looff
    
</code></pre>