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DT_Let.py

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''' The Let tag was contributed to Zope by and is copyright, 1999
    Phillip J. Eby.  Permission has been granted to release the Let tag
    under the Zope Public License.
    

   Let name=value...

   The 'let' tag is used to bind variables to values within a block.

   The text enclosed in the let tag is rendered using information
   from the given variables or expressions.

   For example::

     <!--#let foofunc="foo()" my_bar=bar-->
       foo() = <!--#var foofunc-->,
       bar = <!--#var my_bar-->
     <!--#/let-->

   Notice that both 'name' and 'expr' style attributes may be used to
   specify data.  'name' style attributes (e.g. my_bar=bar) will be
   rendered as they are for var/with/in/etc.  Quoted attributes will
   be treated as Python expressions.

   Variables are processed in sequence, so later assignments can
   reference and/or overwrite the results of previous assignments,
   as desired.
''' 

from DT_Util import render_blocks, Eval, expr_globals, ParseError, regex, strip
from DT_Util import str # Probably needed due to hysterical pickles.


class Let:
    blockContinuations=()
    name='let'
    
    def __init__(self, blocks):
        tname, args, section = blocks[0]
        self.__name__ = args
        self.section = section.blocks
        self.args = args = parse_let_params(args)

        for i in range(len(args)):
            name,expr = args[i]
            if expr[:1]=='"' and expr[-1:]=='"' and len(expr) > 1:
                        # expr shorthand
                expr=expr[1:-1]
                try: args[i] = name, Eval(expr, expr_globals).eval
                except SyntaxError, v:
                    m,(huh,l,c,src) = v
                    raise ParseError, (
                        '<strong>Expression (Python) Syntax error</strong>:'
                        '\n<pre>\n%s\n</pre>\n' % v[0],
                        'let')
    def render(self, md):
        d={}; md._push(d)
        try:
            for name,expr in self.args:
                if type(expr) is type(''): d[name]=md[expr]
                else: d[name]=expr(md)
            return render_blocks(self.section, md)
        finally: md._pop(1)

    __call__ = render

def parse_let_params(text,
            result=None,
            tag='let',
            parmre=regex.compile(
                '\([\0- ]*\([^\0- =\"]+\)=\([^\0- =\"]+\)\)'),
            qparmre=regex.compile(
                '\([\0- ]*\([^\0- =\"]+\)="\([^"]*\)\"\)'),
            **parms):

    result=result or []

    if parmre.match(text) >= 0:
        name=parmre.group(2)
        value=parmre.group(3)
        l=len(parmre.group(1))
    elif qparmre.match(text) >= 0:
        name=qparmre.group(2)
        value='"%s"' % qparmre.group(3)
        l=len(qparmre.group(1))
    else:
        if not text or not strip(text): return result
        raise ParseError, ('invalid parameter: "%s"' % text, tag)
    
    result.append((name,value))

    text=strip(text[l:])
    if text: return apply(parse_let_params,(text,result,tag),parms)
    else: return result


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