diff options
Diffstat (limited to 'Doc/library')
| -rw-r--r-- | Doc/library/collections.rst | 49 | ||||
| -rw-r--r-- | Doc/library/functions.rst | 10 | ||||
| -rw-r--r-- | Doc/library/stdtypes.rst | 9 |
3 files changed, 42 insertions, 26 deletions
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst index 1982187..e01c52e 100644 --- a/Doc/library/collections.rst +++ b/Doc/library/collections.rst @@ -421,27 +421,31 @@ Example:: __slots__ = () - _fields = ('x', 'y') - def __new__(cls, x, y): return tuple.__new__(cls, (x, y)) + _cast = classmethod(tuple.__new__) + def __repr__(self): return 'Point(x=%r, y=%r)' % self - def _asdict(self): + def _asdict(t): 'Return a new dict which maps field names to their values' - return dict(zip(('x', 'y'), self)) + return {'x': t[0], 'y': t[1]} def _replace(self, **kwds): 'Return a new Point object replacing specified fields with new values' - return Point(*map(kwds.get, ('x', 'y'), self)) + return Point._cast(map(kwds.get, ('x', 'y'), self)) + + @property + def _fields(self): + return ('x', 'y') x = property(itemgetter(0)) y = property(itemgetter(1)) >>> p = Point(11, y=22) # instantiate with positional or keyword arguments - >>> p[0] + p[1] # indexable like the regular tuple (11, 22) + >>> p[0] + p[1] # indexable like the plain tuple (11, 22) 33 >>> x, y = p # unpack like a regular tuple >>> x, y @@ -456,33 +460,30 @@ by the :mod:`csv` or :mod:`sqlite3` modules:: EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade') - from itertools import starmap import csv - for record in starmap(EmployeeRecord, csv.reader(open("employees.csv", "rb"))): + for emp in map(EmployeeRecord._cast, csv.reader(open("employees.csv", "rb"))): print(emp.name, emp.title) import sqlite3 conn = sqlite3.connect('/companydata') cursor = conn.cursor() cursor.execute('SELECT name, age, title, department, paygrade FROM employees') - for emp in starmap(EmployeeRecord, cursor.fetchall()): + for emp in map(EmployeeRecord._cast, cursor.fetchall()): print emp.name, emp.title -When casting a single record to a named tuple, use the star-operator [#]_ to unpack -the values:: +In addition to the methods inherited from tuples, named tuples support +three additonal methods and a read-only attribute. - >>> t = [11, 22] - >>> Point(*t) # the star-operator unpacks any iterable object - Point(x=11, y=22) +.. method:: namedtuple._cast(iterable) -When casting a dictionary to a named tuple, use the double-star-operator:: + Class method returning a new instance taking the positional arguments from the *iterable*. + Useful for casting existing sequences and iterables to named tuples: - >>> d = {'x': 11, 'y': 22} - >>> Point(**d) - Point(x=11, y=22) +:: -In addition to the methods inherited from tuples, named tuples support -two additonal methods and a read-only attribute. + >>> t = [11, 22] + >>> Point._cast(t) + Point(x=11, y=22) .. method:: somenamedtuple._asdict() @@ -529,6 +530,12 @@ function: >>> getattr(p, 'x') 11 +When casting a dictionary to a named tuple, use the double-star-operator [#]_:: + + >>> d = {'x': 11, 'y': 22} + >>> Point(**d) + Point(x=11, y=22) + Since a named tuple is a regular Python class, it is easy to add or change functionality. For example, the display format can be changed by overriding the :meth:`__repr__` method: @@ -551,5 +558,5 @@ and customizing it with :meth:`_replace`: .. rubric:: Footnotes -.. [#] For information on the star-operator see +.. [#] For information on the double-star-operator see :ref:`tut-unpacking-arguments` and :ref:`calls`. diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst index 14fd1a7..02c709c2 100644 --- a/Doc/library/functions.rst +++ b/Doc/library/functions.rst @@ -435,7 +435,8 @@ available. They are listed here in alphabetical order. Convert a string or a number to floating point. If the argument is a string, it must contain a possibly signed decimal or floating point number, possibly - embedded in whitespace. Otherwise, the argument may be an integer + embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf. + Otherwise, the argument may be a plain integer or a floating point number, and a floating point number with the same value (within Python's floating point precision) is returned. If no argument is given, returns ``0.0``. @@ -447,9 +448,10 @@ available. They are listed here in alphabetical order. single: Infinity When passing in a string, values for NaN and Infinity may be returned, depending - on the underlying C library. The specific set of strings accepted which cause - these values to be returned depends entirely on the C library and is known to - vary. + on the underlying C library. Float accepts the strings nan, inf and -inf for + NaN and positive or negative infinity. The case and a leading + are ignored as + well as a leading - is ignored for NaN. Float always represents NaN and infinity + as nan, inf or -inf. The float type is described in :ref:`typesnumeric`. diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst index 6dd374f..196ad49 100644 --- a/Doc/library/stdtypes.rst +++ b/Doc/library/stdtypes.rst @@ -285,7 +285,7 @@ numeric operations have a higher priority than comparison operations): +---------------------+---------------------------------+-------+--------------------+ | ``int(x)`` | *x* converted to integer | \(3) | :func:`int` | +---------------------+---------------------------------+-------+--------------------+ -| ``float(x)`` | *x* converted to floating point | | :func:`float` | +| ``float(x)`` | *x* converted to floating point | \(6) | :func:`float` | +---------------------+---------------------------------+-------+--------------------+ | ``complex(re, im)`` | a complex number with real part | | :func:`complex` | | | *re*, imaginary part *im*. | | | @@ -329,6 +329,13 @@ Notes: as in C; see functions :func:`floor` and :func:`ceil` in the :mod:`math` module for well-defined conversions. +(6) + float also accepts the strings "nan" and "inf" with an optional prefix "+" + or "-" for Not a Number (NaN) and positive or negative infinity. + + .. versionadded:: 2.6 + + .. % XXXJH exceptions: overflow (when? what operations?) zerodivision |