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1 """A simple Python template renderer, for a nano-subset of Django syntax.""" | |
2 | |
3 # Coincidentally named the same as http://code.activestate.com/recipes/496702/ | |
4 | |
5 import re, sys | |
6 | |
7 class Templite(object): | |
8 """A simple template renderer, for a nano-subset of Django syntax. | |
9 | |
10 Supported constructs are extended variable access:: | |
11 | |
12 {{var.modifer.modifier|filter|filter}} | |
13 | |
14 loops:: | |
15 | |
16 {% for var in list %}...{% endfor %} | |
17 | |
18 and ifs:: | |
19 | |
20 {% if var %}...{% endif %} | |
21 | |
22 Comments are within curly-hash markers:: | |
23 | |
24 {# This will be ignored #} | |
25 | |
26 Construct a Templite with the template text, then use `render` against a | |
27 dictionary context to create a finished string. | |
28 | |
29 """ | |
30 def __init__(self, text, *contexts): | |
31 """Construct a Templite with the given `text`. | |
32 | |
33 `contexts` are dictionaries of values to use for future renderings. | |
34 These are good for filters and global values. | |
35 | |
36 """ | |
37 self.text = text | |
38 self.context = {} | |
39 for context in contexts: | |
40 self.context.update(context) | |
41 | |
42 # Split the text to form a list of tokens. | |
43 toks = re.split(r"(?s)({{.*?}}|{%.*?%}|{#.*?#})", text) | |
44 | |
45 # Parse the tokens into a nested list of operations. Each item in the | |
46 # list is a tuple with an opcode, and arguments. They'll be | |
47 # interpreted by TempliteEngine. | |
48 # | |
49 # When parsing an action tag with nested content (if, for), the current | |
50 # ops list is pushed onto ops_stack, and the parsing continues in a new | |
51 # ops list that is part of the arguments to the if or for op. | |
52 ops = [] | |
53 ops_stack = [] | |
54 for tok in toks: | |
55 if tok.startswith('{{'): | |
56 # Expression: ('exp', expr) | |
57 ops.append(('exp', tok[2:-2].strip())) | |
58 elif tok.startswith('{#'): | |
59 # Comment: ignore it and move on. | |
60 continue | |
61 elif tok.startswith('{%'): | |
62 # Action tag: split into words and parse further. | |
63 words = tok[2:-2].strip().split() | |
64 if words[0] == 'if': | |
65 # If: ('if', (expr, body_ops)) | |
66 if_ops = [] | |
67 assert len(words) == 2 | |
68 ops.append(('if', (words[1], if_ops))) | |
69 ops_stack.append(ops) | |
70 ops = if_ops | |
71 elif words[0] == 'for': | |
72 # For: ('for', (varname, listexpr, body_ops)) | |
73 assert len(words) == 4 and words[2] == 'in' | |
74 for_ops = [] | |
75 ops.append(('for', (words[1], words[3], for_ops))) | |
76 ops_stack.append(ops) | |
77 ops = for_ops | |
78 elif words[0].startswith('end'): | |
79 # Endsomething. Pop the ops stack | |
80 ops = ops_stack.pop() | |
81 assert ops[-1][0] == words[0][3:] | |
82 else: | |
83 raise SyntaxError("Don't understand tag %r" % words) | |
84 else: | |
85 ops.append(('lit', tok)) | |
86 | |
87 assert not ops_stack, "Unmatched action tag: %r" % ops_stack[-1][0] | |
88 self.ops = ops | |
89 | |
90 def render(self, context=None): | |
91 """Render this template by applying it to `context`. | |
92 | |
93 `context` is a dictionary of values to use in this rendering. | |
94 | |
95 """ | |
96 # Make the complete context we'll use. | |
97 ctx = dict(self.context) | |
98 if context: | |
99 ctx.update(context) | |
100 | |
101 # Run it through an engine, and return the result. | |
102 engine = _TempliteEngine(ctx) | |
103 engine.execute(self.ops) | |
104 return "".join(engine.result) | |
105 | |
106 | |
107 class _TempliteEngine(object): | |
108 """Executes Templite objects to produce strings.""" | |
109 def __init__(self, context): | |
110 self.context = context | |
111 self.result = [] | |
112 | |
113 def execute(self, ops): | |
114 """Execute `ops` in the engine. | |
115 | |
116 Called recursively for the bodies of if's and loops. | |
117 | |
118 """ | |
119 for op, args in ops: | |
120 if op == 'lit': | |
121 self.result.append(args) | |
122 elif op == 'exp': | |
123 try: | |
124 self.result.append(str(self.evaluate(args))) | |
125 except: | |
126 exc_class, exc, _ = sys.exc_info() | |
127 new_exc = exc_class("Couldn't evaluate {{ %s }}: %s" | |
128 % (args, exc)) | |
129 raise new_exc | |
130 elif op == 'if': | |
131 expr, body = args | |
132 if self.evaluate(expr): | |
133 self.execute(body) | |
134 elif op == 'for': | |
135 var, lis, body = args | |
136 vals = self.evaluate(lis) | |
137 for val in vals: | |
138 self.context[var] = val | |
139 self.execute(body) | |
140 else: | |
141 raise AssertionError("TempliteEngine doesn't grok op %r" % op) | |
142 | |
143 def evaluate(self, expr): | |
144 """Evaluate an expression. | |
145 | |
146 `expr` can have pipes and dots to indicate data access and filtering. | |
147 | |
148 """ | |
149 if "|" in expr: | |
150 pipes = expr.split("|") | |
151 value = self.evaluate(pipes[0]) | |
152 for func in pipes[1:]: | |
153 value = self.evaluate(func)(value) | |
154 elif "." in expr: | |
155 dots = expr.split('.') | |
156 value = self.evaluate(dots[0]) | |
157 for dot in dots[1:]: | |
158 try: | |
159 value = getattr(value, dot) | |
160 except AttributeError: | |
161 value = value[dot] | |
162 if hasattr(value, '__call__'): | |
163 value = value() | |
164 else: | |
165 value = self.context[expr] | |
166 return value | |
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