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from django import template |
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from django.template.base import VariableDoesNotExist |
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from django.template.defaulttags import IfNode |
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from django.template.smartif import IfParser, Literal |
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register = template.Library() |
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# Used as a value for ifdef and ifndef tags |
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undefined = object() |
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class IfDefLiteral(Literal): |
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def eval(self, context): |
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if not self.value in context: |
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# Can't raise an exception here because Operator catches it |
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return undefined |
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class IfDefParser(IfParser): |
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def create_var(self, value): |
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return IfDefLiteral(value) |
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class IfDefNode(IfNode): |
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def __init__(self, defined=True, *args, **kwargs): |
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self.defined = defined |
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super(IfDefNode, self).__init__(*args, **kwargs) |
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def __repr__(self): |
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return "<%s>" % self.__class__.__name__ |
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def render(self, context): |
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for condition, nodelist in self.conditions_nodelists: |
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match = undefined |
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if condition is not None: # if / elif clause |
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try: |
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match = condition.eval(context) |
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except VariableDoesNotExist: |
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pass |
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if condition is None or ( # else clause, always render |
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(self.defined and match is not undefined) or |
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(match is undefined and not self.defined)): |
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return nodelist.render(context) |
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return '' |
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def _gen_ifdef(parser, token, block_tokens, defined): |
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# {% if ... %} |
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bits = token.split_contents()[1:] |
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condition = IfDefParser(bits).parse() |
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nodelist = parser.parse(block_tokens) |
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conditions_nodelists = [(condition, nodelist)] |
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token = parser.next_token() |
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# {% elif ... %} (repeatable) |
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while token.contents.startswith(block_tokens[0]): |
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bits = token.split_contents()[1:] |
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condition = IfDefParser(bits).parse() |
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nodelist = parser.parse(block_tokens) |
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conditions_nodelists.append((condition, nodelist)) |
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token = parser.next_token() |
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# {% else %} (optional) |
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if token.contents == 'else': |
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nodelist = parser.parse(block_tokens[-1:]) |
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conditions_nodelists.append((None, nodelist)) |
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token = parser.next_token() |
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# {% endif %} |
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assert token.contents == block_tokens[-1] |
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return IfDefNode(defined, conditions_nodelists) |
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@register.tag |
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def ifdef(parser, token): |
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"""Check if variable is defined in the context |
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Unlike the {% if %} tag, this renders the block if the variable(s) |
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exist within the context, not only if they are truthy. That is, variables |
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with None, 0 or [] values would also render the block. |
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""" |
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return _gen_ifdef(parser, token, ('elifdef', 'else', 'endifdef'), True) |
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@register.tag |
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def ifndef(parser, token): |
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"""Check if variable is *not* defined in the context |
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This is the opposite of {% ifdef %}. |
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""" |
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return _gen_ifdef(parser, token, ('elifndef', 'else', 'endifndef'), False) |
