#!/usr/bin/env python """This module supports Cheetah's optional NameMapper syntax. Overview ================================================================================ NameMapper provides a simple syntax for accessing Python data structures, functions, and methods from Cheetah. It's called NameMapper because it 'maps' simple 'names' in Cheetah templates to possibly more complex syntax in Python. Its purpose is to make working with Cheetah easy for non-programmers. Specifically, non-programmers using Cheetah should NOT need to be taught (a) what the difference is between an object and a dictionary, (b) what functions and methods are, and (c) what 'self' is. A further aim (d) is to buffer the code in Cheetah templates from changes in the implementation of the Python data structures behind them. Consider this scenario: You are building a customer information system. The designers with you want to use information from your system on the client's website --AND-- they want to understand the display code and so they can maintian it themselves. You write a UI class with a 'customers' method that returns a dictionary of all the customer objects. Each customer object has an 'address' method that returns the a dictionary with information about the customer's address. The designers want to be able to access that information. Using PSP, the display code for the website would look something like the following, assuming your servlet subclasses the class you created for managing customer information: <%= self.customer()[ID].address()['city'] %> (42 chars) Using Cheetah's NameMapper syntax it could be any of the following: $self.customers()[$ID].address()['city'] (39 chars) --OR-- $customers()[$ID].address()['city'] --OR-- $customers()[$ID].address().city --OR-- $customers()[$ID].address.city --OR-- $customers()[$ID].address.city --OR-- $customers[$ID].address.city (27 chars) Which of these would you prefer to explain to the designers, who have no programming experience? The last form is 15 characters shorter than the PSP and, conceptually, is far more accessible. With PHP or ASP, the code would be even messier than the PSP This is a rather extreme example and, of course, you could also just implement '$getCustomer($ID).city' and obey the Law of Demeter (search Google for more on that). But good object orientated design isn't the point here. Details ================================================================================ The parenthesized letters below correspond to the aims in the second paragraph. DICTIONARY ACCESS (a) --------------------- NameMapper allows access to items in a dictionary using the same dotted notation used to access object attributes in Python. This aspect of NameMapper is known as 'Unified Dotted Notation'. For example, with Cheetah it is possible to write:: $customers()['kerr'].address() --OR-- $customers().kerr.address() where the second form is in NameMapper syntax. This only works with dictionary keys that are also valid python identifiers:: regex = '[a-zA-Z_][a-zA-Z_0-9]*' AUTOCALLING (b,d) ----------------- NameMapper automatically detects functions and methods in Cheetah $vars and calls them if the parentheses have been left off. For example if 'a' is an object, 'b' is a method:: $a.b is equivalent to:: $a.b() If b returns a dictionary, then following variations are possible:: $a.b.c --OR-- $a.b().c --OR-- $a.b()['c'] where 'c' is a key in the dictionary that a.b() returns. Further notes: * NameMapper autocalls the function or method without any arguments. Thus autocalling can only be used with functions or methods that either have no arguments or have default values for all arguments. * NameMapper only autocalls functions and methods. Classes and callable object instances will not be autocalled. * Autocalling can be disabled using Cheetah's 'useAutocalling' setting. LEAVING OUT 'self' (c,d) ------------------------ NameMapper makes it possible to access the attributes of a servlet in Cheetah without needing to include 'self' in the variable names. See the NAMESPACE CASCADING section below for details. NAMESPACE CASCADING (d) ----------------------- ... Implementation details ================================================================================ * NameMapper's search order is dictionary keys then object attributes * NameMapper.NotFound is raised if a value can't be found for a name. Performance and the C version ================================================================================ Cheetah comes with both a C version and a Python version of NameMapper. The C version is significantly faster and the exception tracebacks are much easier to read. It's still slower than standard Python syntax, but you won't notice the difference in realistic usage scenarios. Cheetah uses the optimized C version (_namemapper.c) if it has been compiled or falls back to the Python version if not. """ import inspect from pprint import pformat from Cheetah.compat import PY2 if PY2: from collections import Mapping else: from collections.abc import Mapping _INCLUDE_NAMESPACE_REPR_IN_NOTFOUND_EXCEPTIONS = False _ALLOW_WRAPPING_OF_NOTFOUND_EXCEPTIONS = True __all__ = ['NotFound', 'hasKey', 'valueForKey', 'valueForName', 'valueFromSearchList', 'valueFromFrameOrSearchList', 'valueFromFrame', ] if PY2 and not hasattr(inspect.imp, 'get_suffixes'): # This is to fix broken behavior of the inspect module under the # Google App Engine setattr(inspect.imp, 'get_suffixes', lambda: [('.py', 'U', 1)]) # N.B. An attempt is made at the end of this module to import C versions of # these functions. If _namemapper.c has been compiled succesfully and the # import goes smoothly, the Python versions defined here will be replaced with # the C versions. def _raiseNotFoundException(key, namespace): excString = "cannot find '%s'" % key if _INCLUDE_NAMESPACE_REPR_IN_NOTFOUND_EXCEPTIONS: excString += ' in the namespace %s' % pformat(namespace) raise NotFound(excString) def _wrapNotFoundException(exc, fullName, namespace): if not _ALLOW_WRAPPING_OF_NOTFOUND_EXCEPTIONS: raise else: excStr = exc.args[0] if excStr.find('while searching') == -1: # only wrap once! excStr += " while searching for '%s'" % fullName if _INCLUDE_NAMESPACE_REPR_IN_NOTFOUND_EXCEPTIONS: excStr += ' in the namespace %s' % pformat(namespace) exc.args = (excStr,) raise def _isInstanceOrClass(obj): if isinstance(obj, type): # oldstyle return True if hasattr(obj, "__class__"): # newstyle if hasattr(obj, 'mro'): # type/class return True elif (hasattr(obj, '__func__') or hasattr(obj, '__code__') or hasattr(obj, '__self__')): # method, func, or builtin func return False elif hasattr(obj, '__init__'): # instance return True return False def hasKey(obj, key): """Determine if 'obj' has 'key' """ if isinstance(obj, Mapping) and key in obj: return True elif hasattr(obj, key): return True else: return False def _valueForName(obj, name, executeCallables=False): nameChunks = name.split('.') for key in nameChunks: if isinstance(obj, Mapping) and key in obj: nextObj = obj[key] else: try: nextObj = getattr(obj, key) except AttributeError: _raiseNotFoundException(key, obj) if executeCallables and callable(nextObj) and \ not _isInstanceOrClass(nextObj): obj = nextObj() else: obj = nextObj return obj def _namespaces(callerFrame, searchList=None): yield callerFrame.f_locals if searchList: for namespace in searchList: yield namespace yield callerFrame.f_globals yield __builtins__ def hasName(obj, name): # Not in the C version """Determine if 'obj' has the 'name' """ key = name.split('.')[0] if not hasKey(obj, key): return False try: valueForName(obj, name) return True except NotFound: return False try: from Cheetah._namemapper import NotFound, valueForKey, valueForName, \ valueFromSearchList, valueFromFrameOrSearchList, valueFromFrame C_VERSION = True except Exception: class NotFound(LookupError): pass def valueForKey(obj, key): if isinstance(obj, Mapping) and key in obj: return obj[key] elif hasattr(obj, key): return getattr(obj, key) else: _raiseNotFoundException(key, obj) def valueForName(obj, name, executeCallables=False): try: return _valueForName(obj, name, executeCallables) except NotFound as e: _wrapNotFoundException(e, fullName=name, namespace=obj) def valueFromSearchList(searchList, name, executeCallables=False): key = name.split('.')[0] for namespace in searchList: if hasKey(namespace, key): return _valueForName(namespace, name, executeCallables=executeCallables) _raiseNotFoundException(key, searchList) def valueFromFrame(name, executeCallables=False, frame=None): # @@TR consider implementing the C version the same way # at the moment it provides a seperate but mirror implementation # to valueFromFrameOrSearchList try: if not frame: frame = inspect.stack()[1][0] return valueFromFrameOrSearchList( searchList=None, name=name, executeCallables=executeCallables, frame=frame) finally: del frame def valueFromFrameOrSearchList(searchList, name, executeCallables=False, frame=None): def __valueForName(): try: return _valueForName(namespace, name, executeCallables=executeCallables) except NotFound as e: _wrapNotFoundException(e, fullName=name, namespace=searchList) try: if not frame: frame = inspect.stack()[1][0] key = name.split('.')[0] for namespace in _namespaces(frame, searchList): if hasKey(namespace, key): return __valueForName() _raiseNotFoundException(key, searchList) finally: del frame # It is possible with PyPy, Jython or Windows, for example, # that _namemapper.c hasn't been compiled. C_VERSION = False ################################################## # CLASSES class Mixin: """@@ document me""" def valueForName(self, name): return valueForName(self, name) def valueForKey(self, key): return valueForKey(self, key) ################################################## # if run from the command line ## def example(): class A(Mixin): classVar = 'classVar val' def method(self, arg='method 1 default arg'): return arg def method2(self, arg='meth 2 default arg'): return {'item1': arg} def method3(self, arg='meth 3 default'): return arg class B(A): classBvar = 'classBvar val' a = A() a.one = 'valueForOne' def function(whichOne='default'): values = { 'default': 'default output', 'one': 'output option one', 'two': 'output option two' } return values[whichOne] a.dic = { 'func': function, 'method': a.method3, 'item': 'itemval', 'subDict': {'nestedMethod': a.method3} } # b = 'this is local b' print(valueForKey(a.dic, 'subDict')) print(valueForName(a, 'dic.item')) print(valueForName(vars(), 'b')) print(valueForName(__builtins__, 'dir')()) print(valueForName(vars(), 'a.classVar')) print(valueForName(vars(), 'a.dic.func', executeCallables=True)) print(valueForName(vars(), 'a.method2.item1', executeCallables=True)) if __name__ == '__main__': example()