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# expr.py - expression handling functions
#
# Copyright (C) 2011, 2012 Arthur de Jong
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301 USA
"""Module for handling expressions used for LDAP searches.
>>> expr = Expression('foo=$foo')
>>> expr.value(dict(foo='XX'))
'foo=XX'
>>> expr = Expression('foo=${foo:-$bar}')
>>> expr.value(dict(foo='', bar='YY'))
'foo=YY'
>>> expr.value(dict(bar=['YY', 'ZZ']))
'foo=YY'
"""
# exported names
__all__ = ('Expression', )
# TODO: do more expression validity checking
class MyIter(object):
"""Custom iterator-like class with a back() method."""
def __init__(self, value):
self.value = value
self.pos = 0
def next(self):
self.pos += 1
try:
return self.value[self.pos - 1]
except IndexError:
return None
def back(self):
self.pos -= 1
def __iter__(self):
return self
def get_name(self):
"""Read a variable name from the value iterator."""
name = ''
for c in self:
if not c or not c.isalnum():
self.back()
return name
name += c
return name
class DollarExpression(object):
"""Class for handling a variable $xxx ${xxx}, ${xxx:-yyy} or ${xxx:+yyy}
expression."""
def __init__(self, value):
"""Parse the expression as the start of a $-expression."""
self.op = None
self.expr = None
c = value.next()
if c == '{':
self.name = value.get_name()
c = value.next()
if c == '}':
return
self.op = c + value.next()
self.expr = Expression(value, endat='}')
elif c == '(':
self.name = None
self.op = value.get_name()
c = value.next()
if c != '(':
raise ValueError("Expecting '('")
self.expr = Expression(value, endat=')')
c = value.next()
if c != ')':
raise ValueError("Expecting ')'")
else:
value.back()
self.name = value.get_name()
def value(self, variables):
"""Expand the expression using the variables specified."""
# lookup the value
value = variables.get(self.name, '')
if value in (None, [], ()):
value = ''
elif isinstance(value, (list, tuple)):
value = value[0]
# TODO: try to return multiple values, one for each value of the list
if self.op == ':-':
return value if value else self.expr.value(variables)
elif self.op == ':+':
return self.expr.value(variables) if value else ''
elif self.op == 'lower':
return self.expr.value(variables).lower()
elif self.op == 'upper':
return self.expr.value(variables).upper()
return value
def variables(self, results):
"""Add the variables used in the expression to results."""
if self.name:
results.add(self.name)
if self.expr:
self.expr.variables(results)
class Expression(object):
"""Class for parsing and expanding an expression."""
def __init__(self, value, endat=None):
"""Parse the expression as a string."""
if not isinstance(value, MyIter):
self.expression = value
value = MyIter(value)
expr = []
literal = ''
c = value.next()
while c != endat:
if c == '$':
if literal:
expr.append(literal)
expr.append(DollarExpression(value))
literal = ''
elif c == '\\':
literal += value.next()
else:
literal += c
c = value.next()
if literal:
expr.append(literal)
self.expr = expr
def value(self, variables):
"""Expand the expression using the variables specified."""
res = ''
for x in self.expr:
if hasattr(x, 'value'):
res += x.value(variables)
else:
res += x
return res
def variables(self, results=None):
"""Return the variables defined in the expression."""
if not results:
results = set()
for x in self.expr:
if hasattr(x, 'variables'):
x.variables(results)
return results
def __str__(self):
return self.expression
def __repr__(self):
return repr(str(self))
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