MCL/sf/adapt/qemu: comparison symbian-qemu-0.9.1-12/python-2.6.1/Doc/glossary.rst

equal deleted inserted replaced

-:ffa851df0825
+:2fb8b9db1c86
+.. _glossary:
+********
+Glossary
+********
+.. if you add new entries, keep the alphabetical sorting!
+.. glossary::
+``>>>``
+The default Python prompt of the interactive shell.  Often seen for code
+examples which can be executed interactively in the interpreter.
+``...``
+The default Python prompt of the interactive shell when entering code for
+an indented code block or within a pair of matching left and right
+delimiters (parentheses, square brackets or curly braces).
+2to3
+A tool that tries to convert Python 2.x code to Python 3.x code by
+handling most of the incompatibilites which can be detected by parsing the
+source and traversing the parse tree.
+2to3 is available in the standard library as :mod:`lib2to3`; a standalone
+entry point is provided as :file:`Tools/scripts/2to3`.  See
+:ref:`2to3-reference`.
+abstract base class
+Abstract Base Classes (abbreviated ABCs) complement :term:`duck-typing` by
+providing a way to define interfaces when other techniques like :func:`hasattr`
+would be clumsy. Python comes with many builtin ABCs for data structures
+(in the :mod:`collections` module), numbers (in the :mod:`numbers`
+module), and streams (in the :mod:`io` module). You can create your own
+ABC with the :mod:`abc` module.
+argument
+A value passed to a function or method, assigned to a named local
+variable in the function body.  A function or method may have both
+positional arguments and keyword arguments in its definition.
+Positional and keyword arguments may be variable-length: ``*`` accepts
+or passes (if in the function definition or call) several positional
+arguments in a list, while ``**`` does the same for keyword arguments
+in a dictionary.
+Any expression may be used within the argument list, and the evaluated
+value is passed to the local variable.
+attribute
+A value associated with an object which is referenced by name using
+dotted expressions.  For example, if an object *o* has an attribute
+*a* it would be referenced as *o.a*.
+BDFL
+Benevolent Dictator For Life, a.k.a. `Guido van Rossum
+<http://www.python.org/~guido/>`_, Python's creator.
+bytecode
+Python source code is compiled into bytecode, the internal representation
+of a Python program in the interpreter.  The bytecode is also cached in
+``.pyc`` and ``.pyo`` files so that executing the same file is faster the
+second time (recompilation from source to bytecode can be avoided).  This
+"intermediate language" is said to run on a :term:`virtual machine`
+that executes the machine code corresponding to each bytecode.
+class
+A template for creating user-defined objects. Class definitions
+normally contain method definitions which operate on instances of the
+class.
+classic class
+Any class which does not inherit from :class:`object`.  See
+:term:`new-style class`.  Classic classes will be removed in Python 3.0.
+coercion
+The implicit conversion of an instance of one type to another during an
+operation which involves two arguments of the same type.  For example,
+``int(3.15)`` converts the floating point number to the integer ``3``, but
+in ``3+4.5``, each argument is of a different type (one int, one float),
+and both must be converted to the same type before they can be added or it
+will raise a ``TypeError``.  Coercion between two operands can be
+performed with the ``coerce`` builtin function; thus, ``3+4.5`` is
+equivalent to calling ``operator.add(*coerce(3, 4.5))`` and results in
+``operator.add(3.0, 4.5)``.  Without coercion, all arguments of even
+compatible types would have to be normalized to the same value by the
+programmer, e.g., ``float(3)+4.5`` rather than just ``3+4.5``.
+complex number
+An extension of the familiar real number system in which all numbers are
+expressed as a sum of a real part and an imaginary part.  Imaginary
+numbers are real multiples of the imaginary unit (the square root of
+``-1``), often written ``i`` in mathematics or ``j`` in
+engineering. Python has builtin support for complex numbers, which are
+written with this latter notation; the imaginary part is written with a
+``j`` suffix, e.g., ``3+1j``.  To get access to complex equivalents of the
+:mod:`math` module, use :mod:`cmath`.  Use of complex numbers is a fairly
+advanced mathematical feature.  If you're not aware of a need for them,
+it's almost certain you can safely ignore them.
+context manager
+An object which controls the environment seen in a :keyword:`with`
+statement by defining :meth:`__enter__` and :meth:`__exit__` methods.
+See :pep:`343`.
+CPython
+The canonical implementation of the Python programming language.  The
+term "CPython" is used in contexts when necessary to distinguish this
+implementation from others such as Jython or IronPython.
+decorator
+A function returning another function, usually applied as a function
+transformation using the ``@wrapper`` syntax.  Common examples for
+decorators are :func:`classmethod` and :func:`staticmethod`.
+The decorator syntax is merely syntactic sugar, the following two
+function definitions are semantically equivalent::
+def f(...):
+...
+f = staticmethod(f)
+@staticmethod
+def f(...):
+...
+descriptor
+Any *new-style* object which defines the methods :meth:`__get__`,
+:meth:`__set__`, or :meth:`__delete__`.  When a class attribute is a
+descriptor, its special binding behavior is triggered upon attribute
+lookup.  Normally, using *a.b* to get, set or delete an attribute looks up
+the object named *b* in the class dictionary for *a*, but if *b* is a
+descriptor, the respective descriptor method gets called.  Understanding
+descriptors is a key to a deep understanding of Python because they are
+the basis for many features including functions, methods, properties,
+class methods, static methods, and reference to super classes.
+For more information about descriptors' methods, see :ref:`descriptors`.
+dictionary
+An associative array, where arbitrary keys are mapped to values.  The use
+of :class:`dict` closely resembles that for :class:`list`, but the keys can
+be any object with a :meth:`__hash__` function, not just integers.
+Called a hash in Perl.
+docstring
+A string literal which appears as the first expression in a class,
+function or module.  While ignored when the suite is executed, it is
+recognized by the compiler and put into the :attr:`__doc__` attribute
+of the enclosing class, function or module.  Since it is available via
+introspection, it is the canonical place for documentation of the
+object.
+duck-typing
+A pythonic programming style which determines an object's type by inspection
+of its method or attribute signature rather than by explicit relationship
+to some type object ("If it looks like a duck and quacks like a duck, it
+must be a duck.")  By emphasizing interfaces rather than specific types,
+well-designed code improves its flexibility by allowing polymorphic
+substitution.  Duck-typing avoids tests using :func:`type` or
+:func:`isinstance`. (Note, however, that duck-typing can be complemented
+with abstract base classes.) Instead, it typically employs :func:`hasattr`
+tests or :term:`EAFP` programming.
+EAFP
+Easier to ask for forgiveness than permission.  This common Python coding
+style assumes the existence of valid keys or attributes and catches
+exceptions if the assumption proves false.  This clean and fast style is
+characterized by the presence of many :keyword:`try` and :keyword:`except`
+statements.  The technique contrasts with the :term:`LBYL` style
+common to many other languages such as C.
+expression
+A piece of syntax which can be evaluated to some value.  In other words,
+an expression is an accumulation of expression elements like literals, names,
+attribute access, operators or function calls which all return a value.
+In contrast to many other languages, not all language constructs are expressions.
+There are also :term:`statement`\s which cannot be used as expressions,
+such as :keyword:`print` or :keyword:`if`.  Assignments are also statements,
+not expressions.
+extension module
+A module written in C or C++, using Python's C API to interact with the core and
+with user code.
+function
+A series of statements which returns some value to a caller. It can also
+be passed zero or more arguments which may be used in the execution of
+the body. See also :term:`argument` and :term:`method`.
+__future__
+A pseudo module which programmers can use to enable new language features
+which are not compatible with the current interpreter.  For example, the
+expression ``11/4`` currently evaluates to ``2``. If the module in which
+it is executed had enabled *true division* by executing::
+from __future__ import division
+the expression ``11/4`` would evaluate to ``2.75``.  By importing the
+:mod:`__future__` module and evaluating its variables, you can see when a
+new feature was first added to the language and when it will become the
+default::
+>>> import __future__
+>>> __future__.division
+_Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192)
+garbage collection
+The process of freeing memory when it is not used anymore.  Python
+performs garbage collection via reference counting and a cyclic garbage
+collector that is able to detect and break reference cycles.
+generator
+A function which returns an iterator.  It looks like a normal function
+except that values are returned to the caller using a :keyword:`yield`
+statement instead of a :keyword:`return` statement.  Generator functions
+often contain one or more :keyword:`for` or :keyword:`while` loops which
+:keyword:`yield` elements back to the caller.  The function execution is
+stopped at the :keyword:`yield` keyword (returning the result) and is
+resumed there when the next element is requested by calling the
+:meth:`next` method of the returned iterator.
+.. index:: single: generator expression
+generator expression
+An expression that returns a generator.  It looks like a normal expression
+followed by a :keyword:`for` expression defining a loop variable, range,
+and an optional :keyword:`if` expression.  The combined expression
+generates values for an enclosing function::
+>>> sum(i*i for i in range(10))         # sum of squares 0, 1, 4, ... 81
+285
+GIL
+See :term:`global interpreter lock`.
+global interpreter lock
+The lock used by Python threads to assure that only one thread
+executes in the :term:`CPython` :term:`virtual machine` at a time.
+This simplifies the CPython implementation by assuring that no two
+processes can access the same memory at the same time.  Locking the
+entire interpreter makes it easier for the interpreter to be
+multi-threaded, at the expense of much of the parallelism afforded by
+multi-processor machines.  Efforts have been made in the past to
+create a "free-threaded" interpreter (one which locks shared data at a
+much finer granularity), but so far none have been successful because
+performance suffered in the common single-processor case.
+hashable
+An object is *hashable* if it has a hash value which never changes during
+its lifetime (it needs a :meth:`__hash__` method), and can be compared to
+other objects (it needs an :meth:`__eq__` or :meth:`__cmp__` method).
+Hashable objects which compare equal must have the same hash value.
+Hashability makes an object usable as a dictionary key and a set member,
+because these data structures use the hash value internally.
+All of Python's immutable built-in objects are hashable, while no mutable
+containers (such as lists or dictionaries) are.  Objects which are
+instances of user-defined classes are hashable by default; they all
+compare unequal, and their hash value is their :func:`id`.
+IDLE
+An Integrated Development Environment for Python.  IDLE is a basic editor
+and interpreter environment which ships with the standard distribution of
+Python.  Good for beginners, it also serves as clear example code for
+those wanting to implement a moderately sophisticated, multi-platform GUI
+application.
+immutable
+An object with a fixed value.  Immutable objects include numbers, strings and
+tuples.  Such an object cannot be altered.  A new object has to
+be created if a different value has to be stored.  They play an important
+role in places where a constant hash value is needed, for example as a key
+in a dictionary.
+integer division
+Mathematical division discarding any remainder.  For example, the
+expression ``11/4`` currently evaluates to ``2`` in contrast to the
+``2.75`` returned by float division.  Also called *floor division*.
+When dividing two integers the outcome will always be another integer
+(having the floor function applied to it). However, if one of the operands
+is another numeric type (such as a :class:`float`), the result will be
+coerced (see :term:`coercion`) to a common type.  For example, an integer
+divided by a float will result in a float value, possibly with a decimal
+fraction.  Integer division can be forced by using the ``//`` operator
+instead of the ``/`` operator.  See also :term:`__future__`.
+interactive
+Python has an interactive interpreter which means you can enter
+statements and expressions at the interpreter prompt, immediately
+execute them and see their results.  Just launch ``python`` with no
+arguments (possibly by selecting it from your computer's main
+menu). It is a very powerful way to test out new ideas or inspect
+modules and packages (remember ``help(x)``).
+interpreted
+Python is an interpreted language, as opposed to a compiled one,
+though the distinction can be blurry because of the presence of the
+bytecode compiler.  This means that source files can be run directly
+without explicitly creating an executable which is then run.
+Interpreted languages typically have a shorter development/debug cycle
+than compiled ones, though their programs generally also run more
+slowly.  See also :term:`interactive`.
+iterable
+A container object capable of returning its members one at a
+time. Examples of iterables include all sequence types (such as
+:class:`list`, :class:`str`, and :class:`tuple`) and some non-sequence
+types like :class:`dict` and :class:`file` and objects of any classes you
+define with an :meth:`__iter__` or :meth:`__getitem__` method.  Iterables
+can be used in a :keyword:`for` loop and in many other places where a
+sequence is needed (:func:`zip`, :func:`map`, ...).  When an iterable
+object is passed as an argument to the builtin function :func:`iter`, it
+returns an iterator for the object.  This iterator is good for one pass
+over the set of values.  When using iterables, it is usually not necessary
+to call :func:`iter` or deal with iterator objects yourself.  The ``for``
+statement does that automatically for you, creating a temporary unnamed
+variable to hold the iterator for the duration of the loop.  See also
+:term:`iterator`, :term:`sequence`, and :term:`generator`.
+iterator
+An object representing a stream of data.  Repeated calls to the iterator's
+:meth:`next` method return successive items in the stream.  When no more
+data are available a :exc:`StopIteration` exception is raised instead.  At
+this point, the iterator object is exhausted and any further calls to its
+:meth:`next` method just raise :exc:`StopIteration` again.  Iterators are
+required to have an :meth:`__iter__` method that returns the iterator
+object itself so every iterator is also iterable and may be used in most
+places where other iterables are accepted.  One notable exception is code
+which attempts multiple iteration passes.  A container object (such as a
+:class:`list`) produces a fresh new iterator each time you pass it to the
+:func:`iter` function or use it in a :keyword:`for` loop.  Attempting this
+with an iterator will just return the same exhausted iterator object used
+in the previous iteration pass, making it appear like an empty container.
+More information can be found in :ref:`typeiter`.
+keyword argument
+Arguments which are preceded with a ``variable_name=`` in the call.
+The variable name designates the local name in the function to which the
+value is assigned.  ``**`` is used to accept or pass a dictionary of
+keyword arguments.  See :term:`argument`.
+lambda
+An anonymous inline function consisting of a single :term:`expression`
+which is evaluated when the function is called.  The syntax to create
+a lambda function is ``lambda [arguments]: expression``
+LBYL
+Look before you leap.  This coding style explicitly tests for
+pre-conditions before making calls or lookups.  This style contrasts with
+the :term:`EAFP` approach and is characterized by the presence of many
+:keyword:`if` statements.
+list
+A built-in Python :term:`sequence`.  Despite its name it is more akin
+to an array in other languages than to a linked list since access to
+elements are O(1).
+list comprehension
+A compact way to process all or part of the elements in a sequence and
+return a list with the results.  ``result = ["0x%02x" % x for x in
+range(256) if x % 2 == 0]`` generates a list of strings containing
+even hex numbers (0x..) in the range from 0 to 255. The :keyword:`if`
+clause is optional.  If omitted, all elements in ``range(256)`` are
+processed.
+mapping
+A container object (such as :class:`dict`) which supports arbitrary key
+lookups using the special method :meth:`__getitem__`.
+metaclass
+The class of a class.  Class definitions create a class name, a class
+dictionary, and a list of base classes.  The metaclass is responsible for
+taking those three arguments and creating the class.  Most object oriented
+programming languages provide a default implementation.  What makes Python
+special is that it is possible to create custom metaclasses.  Most users
+never need this tool, but when the need arises, metaclasses can provide
+powerful, elegant solutions.  They have been used for logging attribute
+access, adding thread-safety, tracking object creation, implementing
+singletons, and many other tasks.
+More information can be found in :ref:`metaclasses`.
+method
+A function which is defined inside a class body.  If called as an attribute
+of an instance of that class, the method will get the instance object as
+its first :term:`argument` (which is usually called ``self``).
+See :term:`function` and :term:`nested scope`.
+mutable
+Mutable objects can change their value but keep their :func:`id`.  See
+also :term:`immutable`.
+named tuple
+Any tuple subclass whose indexable elements are also accessible using
+named attributes (for example, :func:`time.localtime` returns a
+tuple-like object where the *year* is accessible either with an
+index such as ``t[0]`` or with a named attribute like ``t.tm_year``).
+A named tuple can be a built-in type such as :class:`time.struct_time`,
+or it can be created with a regular class definition.  A full featured
+named tuple can also be created with the factory function
+:func:`collections.namedtuple`.  The latter approach automatically
+provides extra features such as a self-documenting representation like
+``Employee(name='jones', title='programmer')``.
+namespace
+The place where a variable is stored.  Namespaces are implemented as
+dictionaries.  There are the local, global and builtin namespaces as well
+as nested namespaces in objects (in methods).  Namespaces support
+modularity by preventing naming conflicts.  For instance, the functions
+:func:`__builtin__.open` and :func:`os.open` are distinguished by their
+namespaces.  Namespaces also aid readability and maintainability by making
+it clear which module implements a function.  For instance, writing
+:func:`random.seed` or :func:`itertools.izip` makes it clear that those
+functions are implemented by the :mod:`random` and :mod:`itertools`
+modules, respectively.
+nested scope
+The ability to refer to a variable in an enclosing definition.  For
+instance, a function defined inside another function can refer to
+variables in the outer function.  Note that nested scopes work only for
+reference and not for assignment which will always write to the innermost
+scope.  In contrast, local variables both read and write in the innermost
+scope.  Likewise, global variables read and write to the global namespace.
+new-style class
+Any class which inherits from :class:`object`.  This includes all built-in
+types like :class:`list` and :class:`dict`.  Only new-style classes can
+use Python's newer, versatile features like :attr:`__slots__`,
+descriptors, properties, and :meth:`__getattribute__`.
+More information can be found in :ref:`newstyle`.
+object
+Any data with state (attributes or value) and defined behavior
+(methods).  Also the ultimate base class of any :term:`new-style
+class`.
+positional argument
+The arguments assigned to local names inside a function or method,
+determined by the order in which they were given in the call.  ``*`` is
+used to either accept multiple positional arguments (when in the
+definition), or pass several arguments as a list to a function.  See
+:term:`argument`.
+Python 3000
+Nickname for the next major Python version, 3.0 (coined long ago
+when the release of version 3 was something in the distant future.)  This
+is also abbreviated "Py3k".
+Pythonic
+An idea or piece of code which closely follows the most common idioms
+of the Python language, rather than implementing code using concepts
+common to other languages.  For example, a common idiom in Python is
+to loop over all elements of an iterable using a :keyword:`for`
+statement.  Many other languages don't have this type of construct, so
+people unfamiliar with Python sometimes use a numerical counter instead::
+for i in range(len(food)):
+print food[i]
+As opposed to the cleaner, Pythonic method::
+for piece in food:
+print piece
+reference count
+The number of references to an object.  When the reference count of an
+object drops to zero, it is deallocated.  Reference counting is
+generally not visible to Python code, but it is a key element of the
+:term:`CPython` implementation.  The :mod:`sys` module defines a
+:func:`getrefcount` function that programmers can call to return the
+reference count for a particular object.
+__slots__
+A declaration inside a :term:`new-style class` that saves memory by
+pre-declaring space for instance attributes and eliminating instance
+dictionaries.  Though popular, the technique is somewhat tricky to get
+right and is best reserved for rare cases where there are large numbers of
+instances in a memory-critical application.
+sequence
+An :term:`iterable` which supports efficient element access using integer
+indices via the :meth:`__getitem__` special method and defines a
+:meth:`len` method that returns the length of the sequence.
+Some built-in sequence types are :class:`list`, :class:`str`,
+:class:`tuple`, and :class:`unicode`. Note that :class:`dict` also
+supports :meth:`__getitem__` and :meth:`__len__`, but is considered a
+mapping rather than a sequence because the lookups use arbitrary
+:term:`immutable` keys rather than integers.
+slice
+An object usually containing a portion of a :term:`sequence`.  A slice is
+created using the subscript notation, ``[]`` with colons between numbers
+when several are given, such as in ``variable_name[1:3:5]``.  The bracket
+(subscript) notation uses :class:`slice` objects internally (or in older
+versions, :meth:`__getslice__` and :meth:`__setslice__`).
+statement
+A statement is part of a suite (a "block" of code).  A statement is either
+an :term:`expression` or a one of several constructs with a keyword, such
+as :keyword:`if`, :keyword:`while` or :keyword:`print`.
+triple-quoted string
+A string which is bound by three instances of either a quotation mark
+(") or an apostrophe (').  While they don't provide any functionality
+not available with single-quoted strings, they are useful for a number
+of reasons.  They allow you to include unescaped single and double
+quotes within a string and they can span multiple lines without the
+use of the continuation character, making them especially useful when
+writing docstrings.
+type
+The type of a Python object determines what kind of object it is; every
+object has a type.  An object's type is accessible as its
+:attr:`__class__` attribute or can be retrieved with ``type(obj)``.
+virtual machine
+A computer defined entirely in software.  Python's virtual machine
+executes the :term:`bytecode` emitted by the bytecode compiler.
+Zen of Python
+Listing of Python design principles and philosophies that are helpful in
+understanding and using the language.  The listing can be found by typing
+"``import this``" at the interactive prompt.