update the tutorial to use str.format

benjaminp · benjaminp · commit f9ef9881d778 · 2008-05-26T00:54:22.000Z
diff --git a/Doc/tutorial/controlflow.rst b/Doc/tutorial/controlflow.rst
@@ -445,8 +445,8 @@ 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. ::
 
-   def fprintf(file, format, *args):
-       file.write(format % args)
+   def fprintf(file, template, *args):
+       file.write(template.format(args))
 
 
 .. _tut-unpacking-arguments:
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst
@@ -550,7 +550,7 @@ with the :func:`zip` function. ::
    >>> questions = ['name', 'quest', 'favorite color']
    >>> answers = ['lancelot', 'the holy grail', 'blue']
    >>> for q, a in zip(questions, answers):
-   ...     print 'What is your %s?  It is %s.' % (q, a)
+   ...     print 'What is your {0}?  It is {1}.'.format(q, a)
    ...	
    What is your name?  It is lancelot.
    What is your quest?  It is the holy grail.
diff --git a/Doc/tutorial/errors.rst b/Doc/tutorial/errors.rst
@@ -132,7 +132,7 @@ the exception (allowing a caller to handle the exception as well)::
        s = f.readline()
        i = int(s.strip())
    except IOError as (errno, strerror):
-       print "I/O error(%s): %s" % (errno, strerror)
+       print "I/O error({0}): {1}".format(errno, strerror)
    except ValueError:
        print "Could not convert data to an integer."
    except:
diff --git a/Doc/tutorial/floatingpoint.rst b/Doc/tutorial/floatingpoint.rst
@@ -132,9 +132,8 @@ that every float operation can suffer a new rounding error.
 While pathological cases do exist, for most casual use of floating-point
 arithmetic you'll see the result you expect in the end if you simply round the
 display of your final results to the number of decimal digits you expect.
-:func:`str` usually suffices, and for finer control see the discussion of
-Python's ``%`` format operator: the ``%g``, ``%f`` and ``%e`` format codes
-supply flexible and easy ways to round float results for display.
+:func:`str` usually suffices, and for finer control see the :meth:`str.format`
+method's format specifiers in :ref:`formatstrings`.
 
 
 .. _tut-fp-error:
diff --git a/Doc/tutorial/inputoutput.rst b/Doc/tutorial/inputoutput.rst
@@ -27,16 +27,13 @@ first way is to do all the string handling yourself; using string slicing and
 concatenation operations you can create any layout you can imagine.  The
 standard module :mod:`string` contains some useful operations for padding
 strings to a given column width; these will be discussed shortly.  The second
-way is to use the ``%`` operator with a string as the left argument.  The ``%``
-operator interprets the left argument much like a :cfunc:`sprintf`\ -style
-format string to be applied to the right argument, and returns the string
-resulting from this formatting operation.
+way is to use the :meth:`str.format` method.
 
 One question remains, of course: how do you convert values to strings? Luckily,
 Python has ways to convert any value to a string: pass it to the :func:`repr`
 or :func:`str` functions.  Reverse quotes (``````) are equivalent to
-:func:`repr`, but they are no longer used in modern Python code and will likely
-not be in future versions of the language.
+:func:`repr`, but they are no longer used in modern Python code and are removed
+in future versions of the language.
 
 The :func:`str` function is meant to return representations of values which are
 fairly human-readable, while :func:`repr` is meant to generate representations
@@ -94,7 +91,7 @@ Here are two ways to write a table of squares and cubes::
    10 100 1000
 
    >>> for x in range(1,11):
-   ...     print '%2d %3d %4d' % (x, x*x, x*x*x)
+   ...     print '{0:2d} {1:3d} {2:4d}'.format(x, x*x, x*x*x)
    ... 
     1   1    1
     2   4    8
@@ -129,42 +126,91 @@ with zeros.  It understands about plus and minus signs::
    >>> '3.14159265359'.zfill(5)
    '3.14159265359'
 
-Using the ``%`` operator looks like this::
+Basic usage of the :meth:`str.format` method looks like this::
+
+   >>> print 'We are the {0} who say "{1}!"'.format('knights', 'Ni')
+   We are the knights who say "Ni!"
+
+The brackets and characters within them (called format fields) are replaced with
+the objects passed into the format method.  The number in the brackets refers to
+the position of the object passed into the format method. ::
+
+   >>> print '{0} and {1}'.format('spam', 'eggs')
+   spam and eggs
+   >>> print '{1} and {0}'.format('spam', 'eggs')
+   eggs and spam
+
+If keyword arguments are used in the format method, their values are referred to
+by using the name of the argument. ::
+
+   >>> print 'This {food} is {adjective}.'.format(food='spam', adjective='absolutely horrible')
+   This spam is absolutely horrible.
+
+Positional and keyword arguments can be arbitrarily combined::
+
+   >>> print 'The story of {0}, {1}, and {other}.'.format('Bill', 'Manfred', other='Georg')
+   The story of Bill, Manfred, and Georg.
+
+An optional ``':``` and format specifier can follow the field name. This also
+greater control over how the value is formatted.  The following example
+truncates the Pi to three places after the decimal.
 
    >>> import math
-   >>> print 'The value of PI is approximately %5.3f.' % math.pi
+   >>> print 'The value of PI is approximately {0:.3f}.'.format(math.pi)
    The value of PI is approximately 3.142.
 
-If there is more than one format in the string, you need to pass a tuple as
-right operand, as in this example::
+Passing an integer after the ``':'`` will cause that field to be a minimum
+number of characters wide.  This is useful for making tables pretty.::
 
    >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
    >>> for name, phone in table.items():
-   ...     print '%-10s ==> %10d' % (name, phone)
+   ...     print '{0:10} ==> {1:10d}'.format(name, phone)
    ... 
    Jack       ==>       4098
    Dcab       ==>       7678
    Sjoerd     ==>       4127
 
-Most formats work exactly as in C and require that you pass the proper type;
-however, if you don't you get an exception, not a core dump. The ``%s`` format
-is more relaxed: if the corresponding argument is not a string object, it is
-converted to string using the :func:`str` built-in function.  Using ``*`` to
-pass the width or precision in as a separate (integer) argument is supported.
-The C formats ``%n`` and ``%p`` are not supported.
-
 If you have a really long format string that you don't want to split up, it
 would be nice if you could reference the variables to be formatted by name
-instead of by position.  This can be done by using form ``%(name)format``, as
-shown here::
+instead of by position.  This can be done by simply passing the dict and using
+square brackets ``'[]'`` to access the keys ::
+
+   >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
+   >>> print 'Jack: {0[Jack]:d}; Sjoerd: {0[Sjoerd]:d}; Dcab: {0[Dcab]:d}'.format(table)
+   Jack: 4098; Sjoerd: 4127; Dcab: 8637678
+
+This could also be done by passing the table as keyword arguments with the '**'
+notation.::
 
    >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
-   >>> print 'Jack: %(Jack)d; Sjoerd: %(Sjoerd)d; Dcab: %(Dcab)d' % table
+   >>> print 'Jack: {Jack:d}; Sjoerd: {Sjoerd:d}; Dcab: {Dcab:d}'.format(**table)
    Jack: 4098; Sjoerd: 4127; Dcab: 8637678
 
 This is particularly useful in combination with the new built-in :func:`vars`
 function, which returns a dictionary containing all local variables.
 
+For a complete overview of string formating with :meth:`str.format`, see
+:ref:`formatstrings`.
+
+
+Old string formatting
+---------------------
+
+The ``%`` operator can also be used for string formatting. It interprets the
+left argument much like a :cfunc:`sprintf`\ -style format string to be applied
+to the right argument, and returns the string resulting from this formatting
+operation. For example::
+
+   >>> import math
+   >>> print 'The value of PI is approximately %5.3f.' % math.pi
+   The value of PI is approximately 3.142.
+
+Since :meth:`str.format` is quite new, a lot of Python code still uses the ``%``
+operator. However, because this old style of formatting will eventually removed
+from the language :meth:`str.format` should generally be used.
+
+More information can be found in the :ref:`string-formatting` section.
+
 
 .. _tut-files:
 
diff --git a/Doc/tutorial/introduction.rst b/Doc/tutorial/introduction.rst
@@ -372,9 +372,13 @@ The built-in function :func:`len` returns the length of a string::
       Both strings and Unicode strings support a large number of methods for
       basic transformations and searching.
 
+   :ref:`new-string-formatting`
+      Information about string formatting with :meth:`str.format` is described
+      here.
+
    :ref:`string-formatting`
-      The formatting operations invoked when strings and Unicode strings are the
-      left operand of the ``%`` operator are described in more detail here.
+      The old formatting operations invoked when strings and Unicode strings are
+      the left operand of the ``%`` operator are described in more detail here.
 
 
 .. _tut-unicodestrings:
diff --git a/Doc/tutorial/stdlib2.rst b/Doc/tutorial/stdlib2.rst
@@ -116,7 +116,7 @@ placeholders such as the current date, image sequence number, or file format::
    >>> for i, filename in enumerate(photofiles):
    ...     base, ext = os.path.splitext(filename)
    ...     newname = t.substitute(d=date, n=i, f=ext)
-   ...     print '%s --> %s' % (filename, newname)
+   ...     print '{0} --> {1}'.format(filename, newname)
 
    img_1074.jpg --> Ashley_0.jpg
    img_1076.jpg --> Ashley_1.jpg
