decorator.py

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"""
Decorator module, see http://pypi.python.org/pypi/decorator
for the documentation.
"""

__all__ = ["decorator", "FunctionMaker", "deprecated", "getinfo", "new_wrapper"]

import os, sys, re, inspect, warnings

DEF = re.compile('\s*def\s*([_\w][_\w\d]*)\s*\(')

# basic functionality
class FunctionMaker(object):
    """
    An object with the ability to create functions with a given signature.
    It has attributes name, doc, module, signature, defaults, dict and
    methods update and make.
    """
    def __init__(self, func=None, name=None, signature=None,
                 defaults=None, doc=None, module=None, funcdict=None):
        if func:
            # func can also be a class or a callable, but not an instance method
            self.name = func.__name__
            if self.name == '<lambda>': # small hack for lambda functions
                self.name = '_lambda_' 
            self.doc = func.__doc__
            self.module = func.__module__
            if inspect.isfunction(func):
                self.signature = inspect.formatargspec(
                    formatvalue=lambda val: "", *inspect.getargspec(func))[1:-1]
                self.defaults = func.func_defaults
                self.dict = func.__dict__.copy()
        if name:
            self.name = name
        if signature is not None:
            self.signature = signature
        if defaults:
            self.defaults = defaults
        if doc:
            self.doc = doc
        if module:
            self.module = module
        if funcdict:
            self.dict = funcdict
        # check existence required attributes
        assert hasattr(self, 'name')
        if not hasattr(self, 'signature'):
            raise TypeError('You are decorating a non function: %s' % func)

    def update(self, func, **kw):
        "Update the signature of func with the data in self"
        func.__name__ = self.name
        func.__doc__ = getattr(self, 'doc', None)
        func.__dict__ = getattr(self, 'dict', {})
        func.func_defaults = getattr(self, 'defaults', None)
        callermodule = sys._getframe(3).f_globals.get('__name__', '?')
        func.__module__ = getattr(self, 'module', callermodule)
        func.__dict__.update(kw)
 
    def make(self, src_templ, evaldict=None, addsource=False, **attrs):
        "Make a new function from a given template and update the signature"
        src = src_templ % vars(self) # expand name and signature
        evaldict = evaldict or {}
        mo = DEF.match(src)
        if mo is None:
            raise SyntaxError('not a valid function template\n%s' % src)
        name = mo.group(1) # extract the function name
        reserved_names = set([name] + [
            arg.strip(' *') for arg in self.signature.split(',')])
        for n, v in evaldict.iteritems():
            if n in reserved_names:
                raise NameError('%s is overridden in\n%s' % (n, src))
        if not src.endswith('\n'): # add a newline just for safety
            src += '\n'
        try:
            code = compile(src, '<string>', 'single')
            exec code in evaldict
        except:
            print >> sys.stderr, 'Error in generated code:'
            print >> sys.stderr, src
            raise
        func = evaldict[name]
        if addsource:
            attrs['__source__'] = src
        self.update(func, **attrs)
        return func

def decorator(caller, func=None):
    """
    decorator(caller) converts a caller function into a decorator;
    decorator(caller, func) decorates a function using a caller.
    """
    if func is None: # returns a decorator
        fun = FunctionMaker(caller)
        first_arg = inspect.getargspec(caller)[0][0]
        src = 'def %s(%s): return _call_(caller, %s)' % (
            caller.__name__, first_arg, first_arg)
        return fun.make(src, dict(caller=caller, _call_=decorator),
                        undecorated=caller)
    else: # returns a decorated function
        fun = FunctionMaker(func)
        src = """def %(name)s(%(signature)s):
    return _call_(_func_, %(signature)s)"""
        return fun.make(src, dict(_func_=func, _call_=caller), undecorated=func)

###################### deprecated functionality #########################

@decorator
def deprecated(func, *args, **kw):
    "A decorator for deprecated functions"
    warnings.warn(
        ('Calling the deprecated function %r\n'
         'Downgrade to decorator 2.3 if you want to use this functionality')
        % func.__name__, DeprecationWarning, stacklevel=3)
    return func(*args, **kw)

@deprecated
def getinfo(func):
    """
    Returns an info dictionary containing:
    - name (the name of the function : str)
    - argnames (the names of the arguments : list)
    - defaults (the values of the default arguments : tuple)
    - signature (the signature : str)
    - doc (the docstring : str)
    - module (the module name : str)
    - dict (the function __dict__ : str)
    
    >>> def f(self, x=1, y=2, *args, **kw): pass

    >>> info = getinfo(f)

    >>> info["name"]
    'f'
    >>> info["argnames"]
    ['self', 'x', 'y', 'args', 'kw']
    
    >>> info["defaults"]
    (1, 2)

    >>> info["signature"]
    'self, x, y, *args, **kw'
    """
    assert inspect.ismethod(func) or inspect.isfunction(func)
    regargs, varargs, varkwargs, defaults = inspect.getargspec(func)
    argnames = list(regargs)
    if varargs:
        argnames.append(varargs)
    if varkwargs:
        argnames.append(varkwargs)
    signature = inspect.formatargspec(regargs, varargs, varkwargs, defaults,
                                      formatvalue=lambda value: "")[1:-1]
    return dict(name=func.__name__, argnames=argnames, signature=signature,
                defaults = func.func_defaults, doc=func.__doc__,
                module=func.__module__, dict=func.__dict__,
                globals=func.func_globals, closure=func.func_closure)

@deprecated
def update_wrapper(wrapper, model, infodict=None):
    "A replacement for functools.update_wrapper"
    infodict = infodict or getinfo(model)
    wrapper.__name__ = infodict['name']
    wrapper.__doc__ = infodict['doc']
    wrapper.__module__ = infodict['module']
    wrapper.__dict__.update(infodict['dict'])
    wrapper.func_defaults = infodict['defaults']
    wrapper.undecorated = model
    return wrapper

@deprecated
def new_wrapper(wrapper, model):
    """
    An improvement over functools.update_wrapper. The wrapper is a generic
    callable object. It works by generating a copy of the wrapper with the 
    right signature and by updating the copy, not the original.
    Moreovoer, 'model' can be a dictionary with keys 'name', 'doc', 'module',
    'dict', 'defaults'.
    """
    if isinstance(model, dict):
        infodict = model
    else: # assume model is a function
        infodict = getinfo(model)
    assert not '_wrapper_' in infodict["argnames"], (
        '"_wrapper_" is a reserved argument name!')
    src = "lambda %(signature)s: _wrapper_(%(signature)s)" % infodict
    funcopy = eval(src, dict(_wrapper_=wrapper))
    return update_wrapper(funcopy, model, infodict)