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import xml.etree.ElementTree as ET
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class XmlBuilder(object):
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'''Build XML document interpolating value from context using str.format() in
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text data. Grammar for schema is:
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schema = tree
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tree = simple | loop
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simple = (tag_name, attribs_dict?, tree*)
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loop = ('?loop', loop_var_name, tree*)
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where tag_name is an ElementTree tag name, or an XML tag name with prefix
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in namespaces, attribs_dict is a list of key values pairs
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The loop construct allow to iterate one variable, the one named by loop_var_name, of the
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context as a subcontext to pass to sub-schemas inside the loop tuple.
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'''
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schema = None
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encoding = 'us-ascii'
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namespaces = None
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def __init__(self, schema=None, encoding=None, namespaces=None):
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self.namespaces = {}
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if schema is not None:
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self.schema = schema
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if encoding is not None:
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self.encoding = encoding
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if namespaces is not None:
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self.namespaces.update(namespaces)
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def resolve_namespace(self, qname):
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if ':' in qname:
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prefix, name = qname.split(':')
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url = self.namespaces[prefix]
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return '{{{0}}}{1}'.format(url, name)
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return qname
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def build(self, context=None):
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tb = ET.TreeBuilder()
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def helper(schema, context):
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tag = schema[0]
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if tag == '?loop':
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var = schema[1]
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for subcontext in context[var]:
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for subschema in schema[2:]:
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helper(subschema, subcontext)
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return
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if context:
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tag = tag.format(**context)
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tag = self.resolve_namespace(tag)
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template_attribs = schema[1] if (len(schema) > 0
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and isinstance(schema[1], dict)) else None
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attribs = None
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if template_attribs:
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for key, value in template_attribs.items():
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if context:
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key = key.format(**context)
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key = self.resolve_namespace(key)
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value = value.format(**context)
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attribs[key] = value
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tb.start(tag, attribs or {})
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if template_attribs is None:
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children = schema[1:]
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else:
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children = schema[2:]
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for child in children:
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if isinstance(child, basestring):
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if context:
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child = child.format(**context)
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tb.data(child)
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else:
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helper(child, context)
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tb.end(tag)
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helper(self.schema, context)
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return tb.close()
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def string(self, context=None, encoding=encoding):
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return ET.tostring(
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self.build(context=context),
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encoding=encoding or self.encoding)
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