--- rest25/tutorial/controlflow.rst	2008-12-19 16:58:06.000000000 +0900
+++ rest262/tutorial/controlflow.rst	2009-04-05 05:01:50.000000000 +0900
@@ -8,84 +8,83 @@
 control flow statements known from other languages, with some twists.
 
 
 .. _tut-if:
 
 :keyword:`if` Statements
 ========================
 
 Perhaps the most well-known statement type is the :keyword:`if` statement.  For
 example::
 
    >>> x = int(raw_input("Please enter an integer: "))
+   Please enter an integer: 42
    >>> if x < 0:
    ...      x = 0
    ...      print 'Negative changed to zero'
    ... elif x == 0:
    ...      print 'Zero'
    ... elif x == 1:
    ...      print 'Single'
    ... else:
    ...      print 'More'
-   ... 
+   ...
+   More
 
 There can be zero or more :keyword:`elif` parts, and the :keyword:`else` part is
 optional.  The keyword ':keyword:`elif`' is short for 'else if', and is useful
 to avoid excessive indentation.  An  :keyword:`if` ... :keyword:`elif` ...
-:keyword:`elif` ... sequence is a substitute for the :keyword:`switch` or
-:keyword:`case` statements found in other languages.
-
-.. % Weird spacings happen here if the wrapping of the source text
-.. % gets changed in the wrong way.
+:keyword:`elif` ... sequence is a substitute for the ``switch`` or
+``case`` statements found in other languages.
 
 
 .. _tut-for:
 
 :keyword:`for` Statements
 =========================
 
 .. index::
    statement: for
    statement: for
 
 The :keyword:`for` statement in Python differs a bit from what you may be used
 to in C or Pascal.  Rather than always iterating over an arithmetic progression
 of numbers (like in Pascal), or giving the user the ability to define both the
 iteration step and halting condition (as C), Python's :keyword:`for` statement
 iterates over the items of any sequence (a list or a string), in the order that
 they appear in the sequence.  For example (no pun intended):
 
-.. % One suggestion was to give a real C example here, but that may only
-.. % serve to confuse non-C programmers.
+.. One suggestion was to give a real C example here, but that may only serve to
+   confuse non-C programmers.
 
 ::
 
    >>> # Measure some strings:
    ... a = ['cat', 'window', 'defenestrate']
    >>> for x in a:
    ...     print x, len(x)
-   ... 
+   ...
    cat 3
    window 6
    defenestrate 12
 
 It is not safe to modify the sequence being iterated over in the loop (this can
 only happen for mutable sequence types, such as lists).  If you need to modify
 the list you are iterating over (for example, to duplicate selected items) you
 must iterate over a copy.  The slice notation makes this particularly
 convenient::
 
    >>> for x in a[:]: # make a slice copy of the entire list
    ...    if len(x) > 6: a.insert(0, x)
-   ... 
+   ...
    >>> a
    ['defenestrate', 'cat', 'window', 'defenestrate']
 
 
 .. _tut-range:
 
 The :func:`range` Function
 ==========================
 
 If you do need to iterate over a sequence of numbers, the built-in function
 :func:`range` comes in handy.  It generates lists containing arithmetic
 progressions::
@@ -96,37 +95,40 @@
 The given end point is never part of the generated list; ``range(10)`` generates
 a list of 10 values, the legal indices for items of a sequence of length 10.  It
 is possible to let the range start at another number, or to specify a different
 increment (even negative; sometimes this is called the 'step')::
 
    >>> range(5, 10)
    [5, 6, 7, 8, 9]
    >>> range(0, 10, 3)
    [0, 3, 6, 9]
    >>> range(-10, -100, -30)
    [-10, -40, -70]
 
-To iterate over the indices of a sequence, combine :func:`range` and :func:`len`
-as follows::
+To iterate over the indices of a sequence, you can combine :func:`range` and
+:func:`len` as follows::
 
    >>> a = ['Mary', 'had', 'a', 'little', 'lamb']
    >>> for i in range(len(a)):
    ...     print i, a[i]
-   ... 
+   ...
    0 Mary
    1 had
    2 a
    3 little
    4 lamb
 
+In most such cases, however, it is convenient to use the :func:`enumerate`
+function, see :ref:`tut-loopidioms`.
+
 
 .. _tut-break:
 
 :keyword:`break` and :keyword:`continue` Statements, and :keyword:`else` Clauses on Loops
 =========================================================================================
 
 The :keyword:`break` statement, like in C, breaks out of the smallest enclosing
 :keyword:`for` or :keyword:`while` loop.
 
 The :keyword:`continue` statement, also borrowed from C, continues with the next
 iteration of the loop.
 
@@ -135,141 +137,156 @@
 condition becomes false (with :keyword:`while`), but not when the loop is
 terminated by a :keyword:`break` statement.  This is exemplified by the
 following loop, which searches for prime numbers::
 
    >>> for n in range(2, 10):
    ...     for x in range(2, n):
    ...         if n % x == 0:
    ...             print n, 'equals', x, '*', n/x
    ...             break
    ...     else:
    ...         # loop fell through without finding a factor
    ...         print n, 'is a prime number'
-   ... 
+   ...
    2 is a prime number
    3 is a prime number
    4 equals 2 * 2
    5 is a prime number
    6 equals 2 * 3
    7 is a prime number
    8 equals 2 * 4
    9 equals 3 * 3
 
 
 .. _tut-pass:
 
 :keyword:`pass` Statements
 ==========================
 
 The :keyword:`pass` statement does nothing. It can be used when a statement is
 required syntactically but the program requires no action. For example::
 
    >>> while True:
-   ...       pass # Busy-wait for keyboard interrupt
-   ... 
+   ...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)
+   ...
+
+This is commonly used for creating minimal classes::
+
+   >>> class MyEmptyClass:
+   ...     pass
+   ...
 
+Another place :keyword:`pass` can be used is as a place-holder for a function or
+conditional body when you are working on new code, allowing you to keep thinking
+at a more abstract level.  The :keyword:`pass` is silently ignored::
+
+   >>> def initlog(*args):
+   ...     pass   # Remember to implement this!
+   ...
 
 .. _tut-functions:
 
 Defining Functions
 ==================
 
 We can create a function that writes the Fibonacci series to an arbitrary
 boundary::
 
    >>> def fib(n):    # write Fibonacci series up to n
    ...     """Print a Fibonacci series up to n."""
    ...     a, b = 0, 1
    ...     while b < n:
    ...         print b,
    ...         a, b = b, a+b
-   ... 
+   ...
    >>> # Now call the function we just defined:
    ... fib(2000)
    1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
 
 .. index::
    single: documentation strings
    single: docstrings
    single: strings, documentation
 
 The keyword :keyword:`def` introduces a function *definition*.  It must be
 followed by the function name and the parenthesized list of formal parameters.
 The statements that form the body of the function start at the next line, and
-must be indented.  The first statement of the function body can optionally be a
-string literal; this string literal is the function's documentation string, or
-:dfn:`docstring`.
+must be indented.
 
+The first statement of the function body can optionally be a string literal;
+this string literal is the function's documentation string, or :dfn:`docstring`.
+(More about docstrings can be found in the section :ref:`tut-docstrings`.)
 There are tools which use docstrings to automatically produce online or printed
 documentation, or to let the user interactively browse through code; it's good
-practice to include docstrings in code that you write, so try to make a habit of
-it.
+practice to include docstrings in code that you write, so make a habit of it.
 
 The *execution* of a function introduces a new symbol table used for the local
 variables of the function.  More precisely, all variable assignments in a
 function store the value in the local symbol table; whereas variable references
-first look in the local symbol table, then in the global symbol table, and then
-in the table of built-in names. Thus,  global variables cannot be directly
-assigned a value within a function (unless named in a :keyword:`global`
-statement), although they may be referenced.
+first look in the local symbol table, then in the local symbol tables of
+enclosing functions, then in the global symbol table, and finally in the table
+of built-in names. Thus, global variables cannot be directly assigned a value
+within a function (unless named in a :keyword:`global` statement), although they
+may be referenced.
 
 The actual parameters (arguments) to a function call are introduced in the local
 symbol table of the called function when it is called; thus, arguments are
 passed using *call by value* (where the *value* is always an object *reference*,
 not the value of the object). [#]_ When a function calls another function, a new
 local symbol table is created for that call.
 
 A function definition introduces the function name in the current symbol table.
 The value of the function name has a type that is recognized by the interpreter
 as a user-defined function.  This value can be assigned to another name which
 can then also be used as a function.  This serves as a general renaming
 mechanism::
 
    >>> fib
    <function fib at 10042ed0>
    >>> f = fib
    >>> f(100)
    1 1 2 3 5 8 13 21 34 55 89
 
-You might object that ``fib`` is not a function but a procedure.  In Python,
-like in C, procedures are just functions that don't return a value.  In fact,
-technically speaking, procedures do return a value, albeit a rather boring one.
-This value is called ``None`` (it's a built-in name).  Writing the value
-``None`` is normally suppressed by the interpreter if it would be the only value
-written.  You can see it if you really want to::
+Coming from other languages, you might object that ``fib`` is not a function but
+a procedure since it doesn't return a value.  In fact, even functions without a
+:keyword:`return` statement do return a value, albeit a rather boring one.  This
+value is called ``None`` (it's a built-in name).  Writing the value ``None`` is
+normally suppressed by the interpreter if it would be the only value written.
+You can see it if you really want to using :keyword:`print`::
 
+   >>> fib(0)
    >>> print fib(0)
    None
 
 It is simple to write a function that returns a list of the numbers of the
 Fibonacci series, instead of printing it::
 
    >>> def fib2(n): # return Fibonacci series up to n
    ...     """Return a list containing the Fibonacci series up to n."""
    ...     result = []
    ...     a, b = 0, 1
    ...     while b < n:
    ...         result.append(b)    # see below
    ...         a, b = b, a+b
    ...     return result
-   ... 
+   ...
    >>> f100 = fib2(100)    # call it
    >>> f100                # write the result
    [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
 
 This example, as usual, demonstrates some new Python features:
 
 * The :keyword:`return` statement returns with a value from a function.
   :keyword:`return` without an expression argument returns ``None``. Falling off
-  the end of a procedure also returns ``None``.
+  the end of a function also returns ``None``.
 
 * The statement ``result.append(b)`` calls a *method* of the list object
   ``result``.  A method is a function that 'belongs' to an object and is named
   ``obj.methodname``, where ``obj`` is some object (this may be an expression),
   and ``methodname`` is the name of a method that is defined by the object's type.
   Different types define different methods.  Methods of different types may have
   the same name without causing ambiguity.  (It is possible to define your own
   object types and methods, using *classes*, as discussed later in this tutorial.)
   The method :meth:`append` shown in the example is defined for list objects; it
   adds a new element at the end of the list.  In this example it is equivalent to
   ``result = result + [b]``, but more efficient.
 
@@ -377,103 +394,109 @@
    parrot(110, voltage=220)     # duplicate value for argument
    parrot(actor='John Cleese')  # unknown keyword
 
 In general, an argument list must have any positional arguments followed by any
 keyword arguments, where the keywords must be chosen from the formal parameter
 names.  It's not important whether a formal parameter has a default value or
 not.  No argument may receive a value more than once --- formal parameter names
 corresponding to positional arguments cannot be used as keywords in the same
 calls. Here's an example that fails due to this restriction::
 
    >>> def function(a):
    ...     pass
-   ... 
+   ...
    >>> function(0, a=0)
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
    TypeError: function() got multiple values for keyword argument 'a'
 
 When a final formal parameter of the form ``**name`` is present, it receives a
-dictionary (XXX reference: ../lib/typesmapping.html) containing all keyword
-arguments except for those corresponding to a formal parameter.  This may be
-combined with a formal parameter of the form ``*name`` (described in the next
-subsection) which receives a tuple containing the positional arguments beyond
-the formal parameter list.  (``*name`` must occur before ``**name``.) For
-example, if we define a function like this::
+dictionary (see :ref:`typesmapping`) containing all keyword arguments except for
+those corresponding to a formal parameter.  This may be combined with a formal
+parameter of the form ``*name`` (described in the next subsection) which
+receives a tuple containing the positional arguments beyond the formal parameter
+list.  (``*name`` must occur before ``**name``.) For example, if we define a
+function like this::
 
    def cheeseshop(kind, *arguments, **keywords):
-       print "-- Do you have any", kind, '?'
+       print "-- Do you have any", kind, "?"
        print "-- I'm sorry, we're all out of", kind
        for arg in arguments: print arg
-       print '-'*40
+       print "-" * 40
        keys = keywords.keys()
        keys.sort()
-       for kw in keys: print kw, ':', keywords[kw]
+       for kw in keys: print kw, ":", keywords[kw]
 
 It could be called like this::
 
-   cheeseshop('Limburger', "It's very runny, sir.",
+   cheeseshop("Limburger", "It's very runny, sir.",
               "It's really very, VERY runny, sir.",
-              client='John Cleese',
               shopkeeper='Michael Palin',
-              sketch='Cheese Shop Sketch')
+              client="John Cleese",
+              sketch="Cheese Shop Sketch")
 
 and of course it would print::
 
    -- Do you have any Limburger ?
    -- I'm sorry, we're all out of Limburger
    It's very runny, sir.
    It's really very, VERY runny, sir.
    ----------------------------------------
    client : John Cleese
    shopkeeper : Michael Palin
    sketch : Cheese Shop Sketch
 
 Note that the :meth:`sort` method of the list of keyword argument names is
 called before printing the contents of the ``keywords`` dictionary; if this is
 not done, the order in which the arguments are printed is undefined.
 
 
 .. _tut-arbitraryargs:
 
 Arbitrary Argument Lists
 ------------------------
 
+.. index::
+  statement: *
+
 Finally, the least frequently used option is to specify that a function can be
 called with an arbitrary number of arguments.  These arguments will be wrapped
-up in a tuple.  Before the variable number of arguments, zero or more normal
-arguments may occur. ::
+up in a tuple (see :ref:`tut-tuples`).  Before the variable number of arguments,
+zero or more normal arguments may occur. ::
 
-   def fprintf(file, format, *args):
-       file.write(format % args)
+   def write_multiple_items(file, separator, *args):
+       file.write(separator.join(args))
 
 
 .. _tut-unpacking-arguments:
 
 Unpacking Argument Lists
 ------------------------
 
 The reverse situation occurs when the arguments are already in a list or tuple
 but need to be unpacked for a function call requiring separate positional
 arguments.  For instance, the built-in :func:`range` function expects separate
 *start* and *stop* arguments.  If they are not available separately, write the
 function call with the  ``*``\ -operator to unpack the arguments out of a list
 or tuple::
 
    >>> range(3, 6)             # normal call with separate arguments
    [3, 4, 5]
    >>> args = [3, 6]
    >>> range(*args)            # call with arguments unpacked from a list
    [3, 4, 5]
 
+.. index::
+  statement: **
+
 In the same fashion, dictionaries can deliver keyword arguments with the ``**``\
 -operator::
 
    >>> def parrot(voltage, state='a stiff', action='voom'):
    ...     print "-- This parrot wouldn't", action,
    ...     print "if you put", voltage, "volts through it.",
    ...     print "E's", state, "!"
    ...
    >>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
    >>> parrot(**d)
    -- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !
 
@@ -533,30 +556,78 @@
 the entire documentation string.  (We can't use the first line since it is
 generally adjacent to the string's opening quotes so its indentation is not
 apparent in the string literal.)  Whitespace "equivalent" to this indentation is
 then stripped from the start of all lines of the string.  Lines that are
 indented less should not occur, but if they occur all their leading whitespace
 should be stripped.  Equivalence of whitespace should be tested after expansion
 of tabs (to 8 spaces, normally).
 
 Here is an example of a multi-line docstring::
 
    >>> def my_function():
    ...     """Do nothing, but document it.
-   ... 
+   ...
    ...     No, really, it doesn't do anything.
    ...     """
    ...     pass
-   ... 
+   ...
    >>> print my_function.__doc__
    Do nothing, but document it.
 
        No, really, it doesn't do anything.
 
 
+.. _tut-codingstyle:
+
+Intermezzo: Coding Style
+========================
+
+.. sectionauthor:: Georg Brandl <georg@python.org>
+.. index:: pair: coding; style
+
+Now that you are about to write longer, more complex pieces of Python, it is a
+good time to talk about *coding style*.  Most languages can be written (or more
+concise, *formatted*) in different styles; some are more readable than others.
+Making it easy for others to read your code is always a good idea, and adopting
+a nice coding style helps tremendously for that.
+
+For Python, :pep:`8` has emerged as the style guide that most projects adhere to;
+it promotes a very readable and eye-pleasing coding style.  Every Python
+developer should read it at some point; here are the most important points
+extracted for you:
+
+* Use 4-space indentation, and no tabs.
+
+  4 spaces are a good compromise between small indentation (allows greater
+  nesting depth) and large indentation (easier to read).  Tabs introduce
+  confusion, and are best left out.
+
+* Wrap lines so that they don't exceed 79 characters.
+
+  This helps users with small displays and makes it possible to have several
+  code files side-by-side on larger displays.
+
+* Use blank lines to separate functions and classes, and larger blocks of
+  code inside functions.
+
+* When possible, put comments on a line of their own.
+
+* Use docstrings.
+
+* Use spaces around operators and after commas, but not directly inside
+  bracketing constructs: ``a = f(1, 2) + g(3, 4)``.
+
+* Name your classes and functions consistently; the convention is to use
+  ``CamelCase`` for classes and ``lower_case_with_underscores`` for functions
+  and methods.  Always use ``self`` as the name for the first method argument
+  (see :ref:`tut-firstclasses` for more on classes and methods).
+
+* Don't use fancy encodings if your code is meant to be used in international
+  environments.  Plain ASCII works best in any case.
+
 
 .. rubric:: Footnotes
 
-.. [#] Actually, *call by object reference* would be a better description, since if a
-   mutable object is passed, the caller will see any changes the callee makes to it
-   (items inserted into a list).
+.. [#] Actually, *call by object reference* would be a better description,
+   since if a mutable object is passed, the caller will see any changes the
+   callee makes to it (items inserted into a list).
 
