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1 # -*- coding: utf-8 -*-
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2 #
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3 # Copyright (C) 2007 Edgewall Software
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4 # All rights reserved.
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5 #
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6 # This software is licensed as described in the file COPYING, which
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7 # you should have received as part of this distribution. The terms
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8 # are also available at http://genshi.edgewall.org/wiki/License.
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9 #
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10 # This software consists of voluntary contributions made by many
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11 # individuals. For the exact contribution history, see the revision
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12 # history and logs, available at http://genshi.edgewall.org/log/.
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13
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14 """String interpolation routines, i.e. the splitting up a given text into some
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15 parts that are literal strings, and others that are Python expressions.
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16 """
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17
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18 from itertools import chain
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19 import os
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20 from tokenize import tokenprog
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21
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22 from genshi.core import TEXT
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23 from genshi.template.base import TemplateSyntaxError, EXPR
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24 from genshi.template.eval import Expression
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25
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26 __all__ = ['interpolate']
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27 __docformat__ = 'restructuredtext en'
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28
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29 NAMESTART = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_'
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30 NAMECHARS = NAMESTART + '.0123456789'
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31 PREFIX = '$'
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32
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33 def interpolate(text, basedir=None, filename=None, lineno=-1, offset=0,
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34 lookup='lenient'):
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35 """Parse the given string and extract expressions.
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36
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37 This function is a generator that yields `TEXT` events for literal strings,
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38 and `EXPR` events for expressions, depending on the results of parsing the
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39 string.
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40
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41 >>> for kind, data, pos in interpolate("hey ${foo}bar"):
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42 ... print kind, `data`
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43 TEXT u'hey '
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44 EXPR Expression('foo')
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45 TEXT u'bar'
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46
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47 :param text: the text to parse
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48 :param basedir: base directory of the file in which the text was found
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49 (optional)
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50 :param filename: basename of the file in which the text was found (optional)
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51 :param lineno: the line number at which the text was found (optional)
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52 :param offset: the column number at which the text starts in the source
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53 (optional)
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54 :param lookup: the variable lookup mechanism; either "lenient" (the
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55 default), "strict", or a custom lookup class
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56 :return: a list of `TEXT` and `EXPR` events
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57 :raise TemplateSyntaxError: when a syntax error in an expression is
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58 encountered
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59 """
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60 filepath = filename
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61 if filepath and basedir:
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62 filepath = os.path.join(basedir, filepath)
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63 pos = [filepath, lineno, offset]
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64
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65 textbuf = []
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66 textpos = None
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67 for is_expr, chunk in chain(lex(text, pos, filepath), [(True, '')]):
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68 if is_expr:
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69 if textbuf:
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70 yield TEXT, u''.join(textbuf), textpos
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71 del textbuf[:]
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72 textpos = None
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73 if chunk:
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74 try:
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75 expr = Expression(chunk.strip(), pos[0], pos[1],
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76 lookup=lookup)
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77 yield EXPR, expr, tuple(pos)
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78 except SyntaxError, err:
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79 raise TemplateSyntaxError(err, filepath, pos[1],
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80 pos[2] + (err.offset or 0))
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81 else:
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82 textbuf.append(chunk)
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83 if textpos is None:
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84 textpos = tuple(pos)
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85
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86 if '\n' in chunk:
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87 lines = chunk.splitlines()
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88 pos[1] += len(lines) - 1
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89 pos[2] += len(lines[-1])
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90 else:
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91 pos[2] += len(chunk)
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92
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93 def lex(text, textpos, filepath):
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94 offset = pos = 0
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95 end = len(text)
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96 escaped = False
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97
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98 while 1:
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99 if escaped:
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100 offset = text.find(PREFIX, offset + 2)
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101 escaped = False
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102 else:
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103 offset = text.find(PREFIX, pos)
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104 if offset < 0 or offset == end - 1:
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105 break
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106 next = text[offset + 1]
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107
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108 if next == '{':
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109 if offset > pos:
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110 yield False, text[pos:offset]
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111 pos = offset + 2
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112 level = 1
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113 while level:
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114 match = tokenprog.match(text, pos)
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115 if match is None:
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116 raise TemplateSyntaxError('invalid syntax', filepath,
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117 *textpos[1:])
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118 pos = match.end()
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119 tstart, tend = match.regs[3]
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120 token = text[tstart:tend]
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121 if token == '{':
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122 level += 1
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123 elif token == '}':
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124 level -= 1
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125 yield True, text[offset + 2:pos - 1]
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126
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127 elif next in NAMESTART:
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128 if offset > pos:
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129 yield False, text[pos:offset]
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130 pos = offset
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131 pos += 1
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132 while pos < end:
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133 char = text[pos]
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134 if char not in NAMECHARS:
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135 break
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136 pos += 1
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137 yield True, text[offset + 1:pos].strip()
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138
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139 elif not escaped and next == PREFIX:
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140 escaped = True
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141 pos = offset + 1
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142
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143 else:
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144 yield False, text[pos:offset + 1]
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145 pos = offset + 1
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146
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147 if pos < end:
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148 yield False, text[pos:]
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