2008.09.22 00:12


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파이썬(Python)의 클래스 메커니즘은 C++과 Modula-3의 혼합물이다.
C++ 용어로 모든 클래스 맴버(member)는 public이다. 그리고 모든 맴버 함수(member function)은 virtual 이다. 특별한 생성자 혹은 소멸자가 없다.

파이썬에서는 객체를 다룰 때 자바의 reference 개념과 유사한 듯하다.
a = [ 1, 2, 3 ] # 리스트 객체가 a에 의해 참조됨
b = a            # b는 리스트 객체를 참조함.
b[0] = 9        # 리스트 객체의 첫번째 원소를 9로 변경함.. 
print a, b       # 결과는 [9, 2, 3] [9, 2, 3] 임.

위 예제에서 보듯이 a와 b는 같은 객체를 가리킴.

Python Scopes and Name Spaces

namespace 는 이름과 객체들의 매핑이다. 대부분의 namespace는 파이썬의 dictionary들로 구현되어있다.
namespace들의 예로 내장(built-in) 이름(name)들의 집합, 모듈에서의 전역(global) 이름들, 그리고 함수 호출내의 지역(local) 이름들이 있다. 같은 의미로 객체들의 속성들의 집합(set)은 하나의 namespace를 형성한다.
중요한 건 다른 namespace들내의 이름(name)들 간에 절대적인 관계가 없다는 것이다. 예로 두개의 다른 모듈에서 정의된 "maximize"라는 함수는 혼돈없이 정의할 수 있다.

나머진 다음에... -__-

By the way, I use the word attribute for any name following a dot -- for example, in the expression z.real, real is an attribute of the object z. Strictly speaking, references to names in modules are attribute references: in the expression modname.funcname, modname is a module object and funcname is an attribute of it. In this case there happens to be a straightforward mapping between the module's attributes and the global names defined in the module: they share the same namespace! 9.1

Attributes may be read-only or writable. In the latter case, assignment to attributes is possible. Module attributes are writable: you can write "modname.the_answer = 42". Writable attributes may also be deleted with the del statement. For example, "del modname.the_answer" will remove the attribute the_answer from the object named by modname.

Name spaces are created at different moments and have different lifetimes. The namespace containing the built-in names is created when the Python interpreter starts up, and is never deleted. The global namespace for a module is created when the module definition is read in; normally, module namespaces also last until the interpreter quits. The statements executed by the top-level invocation of the interpreter, either read from a script file or interactively, are considered part of a module called __main__, so they have their own global namespace. (The built-in names actually also live in a module; this is called __builtin__.)

The local namespace for a function is created when the function is called, and deleted when the function returns or raises an exception that is not handled within the function. (Actually, forgetting would be a better way to describe what actually happens.) Of course, recursive invocations each have their own local namespace.

A scope is a textual region of a Python program where a namespace is directly accessible. ``Directly accessible'' here means that an unqualified reference to a name attempts to find the name in the namespace.

Although scopes are determined statically, they are used dynamically. At any time during execution, there are at least three nested scopes whose namespaces are directly accessible: the innermost scope, which is searched first, contains the local names; the namespaces of any enclosing functions, which are searched starting with the nearest enclosing scope; the middle scope, searched next, contains the current module's global names; and the outermost scope (searched last) is the namespace containing built-in names.

If a name is declared global, then all references and assignments go directly to the middle scope containing the module's global names. Otherwise, all variables found outside of the innermost scope are read-only (an attempt to write to such a variable will simply create a new local variable in the innermost scope, leaving the identically named outer variable unchanged).

Usually, the local scope references the local names of the (textually) current function. Outside functions, the local scope references the same namespace as the global scope: the module's namespace. Class definitions place yet another namespace in the local scope.

It is important to realize that scopes are determined textually: the global scope of a function defined in a module is that module's namespace, no matter from where or by what alias the function is called. On the other hand, the actual search for names is done dynamically, at run time -- however, the language definition is evolving towards static name resolution, at ``compile'' time, so don't rely on dynamic name resolution! (In fact, local variables are already determined statically.)

A special quirk of Python is that assignments always go into the innermost scope. Assignments do not copy data -- they just bind names to objects. The same is true for deletions: the statement "del x" removes the binding of x from the namespace referenced by the local scope. In fact, all operations that introduce new names use the local scope: in particular, import statements and function definitions bind the module or function name in the local scope. (The global statement can be used to indicate that particular variables live in the global scope.)


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