如何在没有明确接受的情况下将自己变成Python方法

Question

我正在开发一个文档测试框架 - 基本上是PDF的单元测试.测试是框架定义的类实例的(修饰)方法,它们在运行时定位和实例化,并调用方法来执行测试.

我的目标是减少编写测试的人需要关注的古怪Python语法的数量,因为这些人可能是也可能不是Python程序员,甚至根本不是程序员.所以我希望他们能够为方法编写"def foo():"而不是"def foo(self):",但仍然可以使用"self"来访问成员.

在一个普通的程序中,我会认为这是一个可怕的想法,但在像这样的特定于域的语言类程序中,似乎值得一试.

我已经通过使用装饰器成功地从方法签名中消除了自我(实际上,因为我已经为测试用例使用了装饰器,我只是将其滚动到那个),但是"self"不会引用任何内容.测试用例方法.

我已经考虑过使用global for self,甚至提出了一个或多或少有效的实现,但我宁愿污染最小的命名空间,这就是为什么我更愿意将变量直接注入test case方法的本地命名空间.有什么想法吗？

Answer 1

我对这个问题的接受答案非常愚蠢,但我刚刚开始.这是一个更好的方法.这只是经过严格测试,但它有助于演示正确的做这件事的方法.它肯定适用于2.6.5.我还没有测试任何其他版本,但没有操作码硬编码到它,所以它应该像大多数其他2.x代码一样可移植.

add_self 可以作为装饰器应用,但这会失败的目的(为什么不只是键入'self'？)从我的其他答案中调整元类很容易应用这个函数.

import opcode
import types



def instructions(code):
    """Iterates over a code string yielding integer [op, arg] pairs

    If the opcode does not take an argument, just put None in the second part
    """
    code = map(ord, code)
    i, L = 0, len(code)
    extended_arg = 0
    while i < L:
        op = code[i]
        i+= 1
        if op < opcode.HAVE_ARGUMENT:
            yield [op, None]
            continue
        oparg = code[i] + (code[i+1] << 8) + extended_arg
        extended_arg = 0
        i += 2
        if op == opcode.EXTENDED_ARG:
            extended_arg = oparg << 16
            continue
        yield [op, oparg]


def write_instruction(inst):
    """Takes an integer [op, arg] pair and returns a list of character bytecodes"""
    op, oparg = inst
    if oparg is None:
        return [chr(op)]
    elif oparg <= 65536L:
        return [chr(op), chr(oparg & 255), chr((oparg >> 8) & 255)]
    elif oparg <= 4294967296L:
        # The argument is large enough to need 4 bytes and the EXTENDED_ARG opcode
        return [chr(opcode.EXTENDED_ARG),
                chr((oparg >> 16) & 255),
                chr((oparg >> 24) & 255),
                chr(op),
                chr(oparg & 255),
                chr((oparg >> 8) & 255)]
    else:
        raise ValueError("Invalid oparg: {0} is too large".format(oparg))


def add_self(f):
    """Add self to a method

    Creates a new function by prepending the name 'self' to co_varnames, and      
    incrementing co_argcount and co_nlocals. Increase the index of all other locals
    by 1 to compensate. Also removes 'self' from co_names and decrease the index of 
    all names that occur after it by 1. Finally, replace all occurrences of 
    `LOAD_GLOBAL i,j` that make reference to the old 'self' with 'LOAD_FAST 0,0'.   

    Essentially, just create a code object that is exactly the same but has one more
    argument. 
    """
    code_obj = f.func_code
    try:
        self_index = code_obj.co_names.index('self')
    except ValueError:
        raise NotImplementedError("self is not a global")

    # The arguments are just the first co_argcount co_varnames
    varnames = ('self', ) + code_obj.co_varnames   
    names = tuple(name for name in code_obj.co_names if name != 'self')

    code = []

    for inst in instructions(code_obj.co_code):
        op = inst[0]
        if op in opcode.haslocal:
            # The index is now one greater because we added 'self' at the head of
            # the tuple
            inst[1] += 1
        elif op in opcode.hasname:
            arg = inst[1]
            if arg == self_index:
                # This refers to the old global 'self'
                if op == opcode.opmap['LOAD_GLOBAL']:
                    inst[0] = opcode.opmap['LOAD_FAST']
                    inst[1] = 0
                else:
                    # If `self` is used as an attribute, real global, module
                    # name, module attribute, or gets looked at funny, bail out.
                    raise NotImplementedError("Abnormal use of self")
            elif arg > self_index:
                # This rewrites the index to account for the old global 'self'
                # having been removed.
                inst[1] -= 1

        code += write_instruction(inst)

    code = ''.join(code)

    # type help(types.CodeType) at the interpreter prompt for this one   
    new_code_obj = types.CodeType(code_obj.co_argcount + 1,
                                  code_obj.co_nlocals + 1,
                                  code_obj.co_stacksize,
                                  code_obj.co_flags, 
                                  code,
                                  code_obj.co_consts,
                                  names, 
                                  varnames, 
                                  '<OpcodeCity>',
                                  code_obj.co_name,  
                                  code_obj.co_firstlineno,
                                  code_obj.co_lnotab, 
                                  code_obj.co_freevars,
                                  code_obj.co_cellvars)


    # help(types.FunctionType)
    return types.FunctionType(new_code_obj, f.func_globals)



class Test(object):

    msg = 'Foo'

    @add_self
    def show(msg):
        print self.msg + msg


t = Test()
t.show('Bar')

Answer 2

aaronasterling解决方案的升级很少(我没有足够的声誉来评论它):

def wrap(f):
    @functools.wraps(f)
    def wrapper(self,*arg,**kw):
        f.func_globals['self'] = self        
        return f(*arg,**kw)
    return wrapper

但是如果为不同的实例递归调用f函数,这两个解决方案都将无法预测,所以你必须像这样克隆它:

import types
class wrap(object):
    def __init__(self,func):
        self.func = func
    def __get__(self,obj,type):
        new_globals = self.func.func_globals.copy()
        new_globals['self'] = obj
        return types.FunctionType(self.func.func_code,new_globals)
class C(object):
    def __init__(self,word):
        self.greeting = word
    @wrap
    def greet(name):
        print(self.greeting+' , ' + name+ '!')
C('Hello').greet('kindall')

Answer 3

这是一个单行方法装饰器，它似乎可以完成这项工作，而无需修改可调用类型*标记为只读的任何特殊属性：

# method decorator -- makes undeclared 'self' argument available to method
injectself = lambda f: lambda self: eval(f.func_code, dict(self=self))

class TestClass:
    def __init__(self, thing):
        self.attr = thing

    @injectself
    def method():
        print 'in TestClass::method(): self.attr = %r' % self.attr
        return 42

test = TestClass("attribute's value")
ret = test.method()
print 'return value:', ret

# output:
# in TestClass::method(): self.attr = "attribute's value"
# return value: 42

请注意，除非您采取预防措施来防止它，否则该函数的副作用eval()可能是它自动添加一些条目（例如对__builtin__键下模块的引用__builtins__）dict传递给它。

@kendall：根据您关于如何将其与容器类中的方法一起使用的评论（但暂时忽略其他变量的注入）——以下内容是否类似于您正在做的事情？我很难理解框架和用户编写的内容之间是如何划分的。对我来说，这听起来是一个有趣的设计模式。

# method decorator -- makes undeclared 'self' argument available to method
injectself = lambda f: lambda self: eval(f.func_code, dict(self=self))

class methodclass:
    def __call__():
        print 'in methodclass::__call__(): self.attr = %r' % self.attr
        return 42

class TestClass:
    def __init__(self, thing):
        self.attr = thing

    method = injectself(methodclass.__call__)

test = TestClass("attribute's value")
ret = test.method()
print 'return value:', ret

# output
# in methodclass::__call__(): self.attr = "attribute's value"
# return value: 42