1 | """ |
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2 | Generic parsers to use when reading in configuration data |
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3 | - methods available to deal with both XML and INI (flat text key/val) formats |
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4 | """ |
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5 | __author__ = "C Byrom - Tessella" |
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6 | __date__ = "28/08/08" |
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7 | __copyright__ = "(C) 2009 Science and Technology Facilities Council" |
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8 | __license__ = "BSD - see LICENSE file in top-level directory" |
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9 | __contact__ = "Philip.Kershaw@stfc.ac.uk" |
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10 | __revision__ = '$Id: $' |
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11 | import traceback |
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12 | import logging, os, sys |
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13 | log = logging.getLogger(__name__) |
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14 | |
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15 | |
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16 | class ClassFactoryError(Exception): |
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17 | """Exception handling for NDG classfactory module.""" |
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18 | def __init__(self, msg): |
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19 | log.error(msg) |
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20 | Exception.__init__(self, msg) |
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21 | |
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22 | |
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23 | def importClass(moduleName, className=None, objectType=None): |
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24 | '''Import a class from a string module name and class name. |
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25 | |
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26 | @param moduleName: Name of module containing the class |
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27 | @type moduleName: str |
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28 | @param className: Name of the class to import. If none is given, the |
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29 | class name will be assumed to be the last component of modulePath |
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30 | @type className: str |
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31 | @rtype: class object |
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32 | @return: imported class''' |
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33 | |
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34 | if className is None: |
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35 | _moduleName, className = moduleName.rsplit('.', 1) |
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36 | else: |
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37 | _moduleName = moduleName |
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38 | |
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39 | log.debug("Importing class %s ..." % className) |
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40 | |
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41 | module = __import__(_moduleName, globals(), locals(), []) |
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42 | components = _moduleName.split('.') |
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43 | try: |
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44 | for component in components[1:]: |
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45 | module = getattr(module, component) |
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46 | except AttributeError, e: |
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47 | raise AttributeError("Error importing class %s: %s" % |
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48 | (className, traceback.format_exc())) |
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49 | |
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50 | importedClass = getattr(module, className) |
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51 | |
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52 | # Check class inherits from a base class |
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53 | if objectType and not issubclass(importedClass, objectType): |
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54 | raise TypeError("Specified class %s must be derived from %s; got %s" % |
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55 | (className, objectType, importedClass)) |
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56 | |
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57 | log.info('Imported "%s" class from module, "%s"', className, _moduleName) |
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58 | return importedClass |
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59 | |
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60 | |
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61 | def instantiateClass(moduleName, className=None, moduleFilePath=None, |
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62 | objectType=None, classArgs=(), classProperties={}): |
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63 | ''' |
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64 | Create and return an instance of the specified class |
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65 | @param moduleName: Name of module containing the class |
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66 | @type moduleName: str |
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67 | @param className: Name of the class to instantiate. May be None in |
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68 | which case, the class name is parsed from the moduleName last element |
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69 | @type className: str |
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70 | @param moduleFilePath: Path to the module - if unset, assume module on |
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71 | system path already |
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72 | @type moduleFilePath: str |
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73 | @param classProperties: dict of properties to use when instantiating the |
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74 | class |
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75 | @type classProperties: dict |
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76 | @param objectType: expected type for the object to instantiate - to |
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77 | enforce use of specific interfaces |
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78 | @type objectType: object |
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79 | @return: object - instance of the class specified |
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80 | ''' |
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81 | |
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82 | |
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83 | # ensure that classproperties is a dict - NB, it may be passed in as a null |
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84 | # value which can override the default val |
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85 | if not classProperties: |
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86 | classProperties = {} |
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87 | |
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88 | # variable to store original state of the system path |
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89 | sysPathBak = None |
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90 | try: |
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91 | try: |
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92 | # Module file path may be None if the new module to be loaded |
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93 | # can be found in the existing system path |
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94 | if moduleFilePath: |
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95 | if not os.path.exists(moduleFilePath): |
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96 | raise IOError("Module file path '%s' doesn't exist" % |
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97 | moduleFilePath) |
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98 | |
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99 | # Temporarily extend system path ready for import |
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100 | sysPathBak = sys.path |
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101 | |
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102 | sys.path.append(moduleFilePath) |
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103 | |
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104 | |
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105 | # Import module name specified in properties file |
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106 | importedClass = importClass(moduleName, |
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107 | className=className, |
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108 | objectType=objectType) |
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109 | finally: |
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110 | # revert back to original sys path, if necessary |
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111 | # NB, python requires the use of a try/finally OR a try/except |
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112 | # block - not both combined |
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113 | if sysPathBak: |
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114 | sys.path = sysPathBak |
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115 | |
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116 | except Exception, e: |
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117 | log.error('%s module import raised %s type exception: %s' % |
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118 | (moduleName, e.__class__, e)) |
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119 | raise |
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120 | |
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121 | # Instantiate class |
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122 | log.debug('Instantiating class "%s"' % importedClass.__name__) |
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123 | try: |
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124 | if classArgs: |
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125 | object = importedClass(*classArgs, **classProperties) |
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126 | else: |
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127 | object = importedClass(**classProperties) |
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128 | |
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129 | return object |
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130 | |
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131 | except Exception, e: |
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132 | log.error("Instantiating class, %s: %s" % (importedClass.__name__, |
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133 | traceback.format_exc())) |
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134 | raise |
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135 | |
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136 | |
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