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Diffstat (limited to 'Doc/howto')
| -rw-r--r-- | Doc/howto/functional.rst | 144 | ||||
| -rw-r--r-- | Doc/howto/logging-cookbook.rst | 4 | ||||
| -rw-r--r-- | Doc/howto/logging.rst | 4 | ||||
| -rw-r--r-- | Doc/howto/regex.rst | 24 | ||||
| -rw-r--r-- | Doc/howto/urllib2.rst | 2 |
5 files changed, 107 insertions, 71 deletions
diff --git a/Doc/howto/functional.rst b/Doc/howto/functional.rst index 7189c65..97c90c7 100644 --- a/Doc/howto/functional.rst +++ b/Doc/howto/functional.rst @@ -3,7 +3,7 @@ ******************************** :Author: A. M. Kuchling -:Release: 0.31 +:Release: 0.32 In this document, we'll take a tour of Python's features suitable for implementing programs in a functional style. After an introduction to the @@ -15,9 +15,9 @@ concepts of functional programming, we'll look at language features such as Introduction ============ -This section explains the basic concept of functional programming; if you're -just interested in learning about Python language features, skip to the next -section. +This section explains the basic concept of functional programming; if +you're just interested in learning about Python language features, +skip to the next section on :ref:`functional-howto-iterators`. Programming languages support decomposing problems in several different ways: @@ -173,6 +173,8 @@ new programs by arranging existing functions in a new configuration and writing a few functions specialized for the current task. +.. _functional-howto-iterators: + Iterators ========= @@ -670,7 +672,7 @@ indexes at which certain conditions are met:: :func:`sorted(iterable, key=None, reverse=False) <sorted>` collects all the elements of the iterable into a list, sorts the list, and returns the sorted -result. The *key*, and *reverse* arguments are passed through to the +result. The *key* and *reverse* arguments are passed through to the constructed list's :meth:`~list.sort` method. :: >>> import random @@ -836,7 +838,8 @@ Another group of functions chooses a subset of an iterator's elements based on a predicate. :func:`itertools.filterfalse(predicate, iter) <itertools.filterfalse>` is the -opposite, returning all elements for which the predicate returns false:: +opposite of :func:`filter`, returning all elements for which the predicate +returns false:: itertools.filterfalse(is_even, itertools.count()) => 1, 3, 5, 7, 9, 11, 13, 15, ... @@ -864,6 +867,77 @@ iterable's results. :: itertools.dropwhile(is_even, itertools.count()) => 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ... +:func:`itertools.compress(data, selectors) <itertools.compress>` takes two +iterators and returns only those elements of *data* for which the corresponding +element of *selectors* is true, stopping whenever either one is exhausted:: + + itertools.compress([1,2,3,4,5], [True, True, False, False, True]) => + 1, 2, 5 + + +Combinatoric functions +---------------------- + +The :func:`itertools.combinations(iterable, r) <itertools.combinations>` +returns an iterator giving all possible *r*-tuple combinations of the +elements contained in *iterable*. :: + + itertools.combinations([1, 2, 3, 4, 5], 2) => + (1, 2), (1, 3), (1, 4), (1, 5), + (2, 3), (2, 4), (2, 5), + (3, 4), (3, 5), + (4, 5) + + itertools.combinations([1, 2, 3, 4, 5], 3) => + (1, 2, 3), (1, 2, 4), (1, 2, 5), (1, 3, 4), (1, 3, 5), (1, 4, 5), + (2, 3, 4), (2, 3, 5), (2, 4, 5), + (3, 4, 5) + +The elements within each tuple remain in the same order as +*iterable* returned them. For example, the number 1 is always before +2, 3, 4, or 5 in the examples above. A similar function, +:func:`itertools.permutations(iterable, r=None) <itertools.permutations>`, +removes this constraint on the order, returning all possible +arrangements of length *r*:: + + itertools.permutations([1, 2, 3, 4, 5], 2) => + (1, 2), (1, 3), (1, 4), (1, 5), + (2, 1), (2, 3), (2, 4), (2, 5), + (3, 1), (3, 2), (3, 4), (3, 5), + (4, 1), (4, 2), (4, 3), (4, 5), + (5, 1), (5, 2), (5, 3), (5, 4) + + itertools.permutations([1, 2, 3, 4, 5]) => + (1, 2, 3, 4, 5), (1, 2, 3, 5, 4), (1, 2, 4, 3, 5), + ... + (5, 4, 3, 2, 1) + +If you don't supply a value for *r* the length of the iterable is used, +meaning that all the elements are permuted. + +Note that these functions produce all of the possible combinations by +position and don't require that the contents of *iterable* are unique:: + + itertools.permutations('aba', 3) => + ('a', 'b', 'a'), ('a', 'a', 'b'), ('b', 'a', 'a'), + ('b', 'a', 'a'), ('a', 'a', 'b'), ('a', 'b', 'a') + +The identical tuple ``('a', 'a', 'b')`` occurs twice, but the two 'a' +strings came from different positions. + +The :func:`itertools.combinations_with_replacement(iterable, r) <itertools.combinations_with_replacement>` +function relaxes a different constraint: elements can be repeated +within a single tuple. Conceptually an element is selected for the +first position of each tuple and then is replaced before the second +element is selected. :: + + itertools.combinations_with_replacement([1, 2, 3, 4, 5], 2) => + (1, 1), (1, 2), (1, 3), (1, 4), (1, 5), + (2, 2), (2, 3), (2, 4), (2, 5), + (3, 3), (3, 4), (3, 5), + (4, 4), (4, 5), + (5, 5) + Grouping elements ----------------- @@ -986,6 +1060,17 @@ write the obvious :keyword:`for` loop:: for i in [1,2,3]: product *= i +A related function is `itertools.accumulate(iterable, func=operator.add) <itertools.accumulate`. +It performs the same calculation, but instead of returning only the +final result, :func:`accumulate` returns an iterator that also yields +each partial result:: + + itertools.accumulate([1,2,3,4,5]) => + 1, 3, 6, 10, 15 + + itertools.accumulate([1,2,3,4,5], operator.mul) => + 1, 2, 6, 24, 120 + The operator module ------------------- @@ -1159,51 +1244,6 @@ features in Python 2.5. .. comment - Topics to place - ----------------------------- - - XXX os.walk() - - XXX Need a large example. - - But will an example add much? I'll post a first draft and see - what the comments say. - -.. comment - - Original outline: - Introduction - Idea of FP - Programs built out of functions - Functions are strictly input-output, no internal state - Opposed to OO programming, where objects have state - - Why FP? - Formal provability - Assignment is difficult to reason about - Not very relevant to Python - Modularity - Small functions that do one thing - Debuggability: - Easy to test due to lack of state - Easy to verify output from intermediate steps - Composability - You assemble a toolbox of functions that can be mixed - - Tackling a problem - Need a significant example - - Iterators - Generators - The itertools module - List comprehensions - Small functions and the lambda statement - Built-in functions - map - filter - -.. comment - Handy little function for printing part of an iterator -- used while writing this document. @@ -1214,5 +1254,3 @@ features in Python 2.5. sys.stdout.write(str(elem)) sys.stdout.write(', ') print(elem[-1]) - - diff --git a/Doc/howto/logging-cookbook.rst b/Doc/howto/logging-cookbook.rst index 3f256e1..feb9b6c 100644 --- a/Doc/howto/logging-cookbook.rst +++ b/Doc/howto/logging-cookbook.rst @@ -704,9 +704,7 @@ the basis for code meeting your own specific requirements:: break logger = logging.getLogger(record.name) logger.handle(record) # No level or filter logic applied - just do it! - except (KeyboardInterrupt, SystemExit): - raise - except: + except Exception: import sys, traceback print('Whoops! Problem:', file=sys.stderr) traceback.print_exc(file=sys.stderr) diff --git a/Doc/howto/logging.rst b/Doc/howto/logging.rst index 6cd0677..a5e24b0 100644 --- a/Doc/howto/logging.rst +++ b/Doc/howto/logging.rst @@ -901,10 +901,10 @@ provided: disk files, rotating the log file at certain timed intervals. #. :class:`~handlers.SocketHandler` instances send messages to TCP/IP - sockets. + sockets. Since 3.4, Unix domain sockets are also supported. #. :class:`~handlers.DatagramHandler` instances send messages to UDP - sockets. + sockets. Since 3.4, Unix domain sockets are also supported. #. :class:`~handlers.SMTPHandler` instances send messages to a designated email address. diff --git a/Doc/howto/regex.rst b/Doc/howto/regex.rst index 5203e53..fbe763b 100644 --- a/Doc/howto/regex.rst +++ b/Doc/howto/regex.rst @@ -271,8 +271,8 @@ performing string substitutions. :: >>> import re >>> p = re.compile('ab*') - >>> p #doctest: +ELLIPSIS - <_sre.SRE_Pattern object at 0x...> + >>> p + re.compile('ab*') :func:`re.compile` also accepts an optional *flags* argument, used to enable various special features and syntax variations. We'll go over the available @@ -383,8 +383,8 @@ Python interpreter, import the :mod:`re` module, and compile a RE:: >>> import re >>> p = re.compile('[a-z]+') - >>> p #doctest: +ELLIPSIS - <_sre.SRE_Pattern object at 0x...> + >>> p + re.compile('[a-z]+') Now, you can try matching various strings against the RE ``[a-z]+``. An empty string shouldn't match at all, since ``+`` means 'one or more repetitions'. @@ -402,7 +402,7 @@ should store the result in a variable for later use. :: >>> m = p.match('tempo') >>> m #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(0, 5), match='tempo'> Now you can query the :ref:`match object <match-objects>` for information about the matching string. :ref:`match object <match-objects>` instances @@ -441,7 +441,7 @@ case. :: >>> print(p.match('::: message')) None >>> m = p.search('::: message'); print(m) #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(4, 11), match='message'> >>> m.group() 'message' >>> m.span() @@ -493,7 +493,7 @@ the RE string added as the first argument, and still return either ``None`` or a >>> print(re.match(r'From\s+', 'Fromage amk')) None >>> re.match(r'From\s+', 'From amk Thu May 14 19:12:10 1998') #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(0, 5), match='From '> Under the hood, these functions simply create a pattern object for you and call the appropriate method on it. They also store the compiled @@ -685,7 +685,7 @@ given location, they can obviously be matched an infinite number of times. line, the RE to use is ``^From``. :: >>> print(re.search('^From', 'From Here to Eternity')) #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(0, 4), match='From'> >>> print(re.search('^From', 'Reciting From Memory')) None @@ -697,11 +697,11 @@ given location, they can obviously be matched an infinite number of times. or any location followed by a newline character. :: >>> print(re.search('}$', '{block}')) #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(6, 7), match='}'> >>> print(re.search('}$', '{block} ')) None >>> print(re.search('}$', '{block}\n')) #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(6, 7), match='}'> To match a literal ``'$'``, use ``\$`` or enclose it inside a character class, as in ``[$]``. @@ -726,7 +726,7 @@ given location, they can obviously be matched an infinite number of times. >>> p = re.compile(r'\bclass\b') >>> print(p.search('no class at all')) #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(3, 8), match='class'> >>> print(p.search('the declassified algorithm')) None >>> print(p.search('one subclass is')) @@ -744,7 +744,7 @@ given location, they can obviously be matched an infinite number of times. >>> print(p.search('no class at all')) None >>> print(p.search('\b' + 'class' + '\b')) #doctest: +ELLIPSIS - <_sre.SRE_Match object at 0x...> + <_sre.SRE_Match object; span=(0, 7), match='\x08class\x08'> Second, inside a character class, where there's no use for this assertion, ``\b`` represents the backspace character, for compatibility with Python's diff --git a/Doc/howto/urllib2.rst b/Doc/howto/urllib2.rst index 74eeee0..7b217ea 100644 --- a/Doc/howto/urllib2.rst +++ b/Doc/howto/urllib2.rst @@ -507,7 +507,7 @@ than the URL you pass to .add_password() will also match. :: -- ``ProxyHandler`` (if a proxy setting such as an :envvar:`http_proxy` environment variable is set), ``UnknownHandler``, ``HTTPHandler``, ``HTTPDefaultErrorHandler``, ``HTTPRedirectHandler``, ``FTPHandler``, - ``FileHandler``, ``HTTPErrorProcessor``. + ``FileHandler``, ``DataHandler``, ``HTTPErrorProcessor``. ``top_level_url`` is in fact *either* a full URL (including the 'http:' scheme component and the hostname and optionally the port number) |