path: root/rdflib/util.py

"""
Some utility functions.

Miscellaneous utilities

* list2set
* first
* uniq
* more_than

Term characterisation and generation

* to_term
* from_n3

Date/time utilities

* date_time
* parse_date_time

Statement and component type checkers

* check_context
* check_subject
* check_predicate
* check_object
* check_statement
* check_pattern

"""

from calendar import timegm
from time import altzone
# from time import daylight
from time import gmtime
from time import localtime
from time import time
from time import timezone

from os.path import splitext
from StringIO import StringIO

from rdflib.exceptions import ContextTypeError
from rdflib.exceptions import ObjectTypeError
from rdflib.exceptions import PredicateTypeError
from rdflib.exceptions import SubjectTypeError
from rdflib.graph import Graph
from rdflib.graph import QuotedGraph
from rdflib.namespace import Namespace
from rdflib.namespace import NamespaceManager
from rdflib.term import BNode
from rdflib.term import Literal
from rdflib.term import URIRef
from rdflib.py3compat import sign

__all__ = [
    'list2set', 'first', 'uniq', 'more_than', 'to_term', 'from_n3',
    'date_time', 'parse_date_time', 'check_context', 'check_subject',
    'check_predicate', 'check_object', 'check_statement', 'check_pattern',
    'guess_format', 'find_roots', 'get_tree']


def list2set(seq):
    """
    Return a new list without duplicates.
    Preserves the order, unlike set(seq)
    """
    seen = set()
    return [x for x in seq if x not in seen and not seen.add(x)]


def first(seq):
    """
    return the first element in a python sequence
    for graphs, use graph.value instead
    """
    for result in seq:
        return result
    return None


def uniq(sequence, strip=0):
    """removes duplicate strings from the sequence."""
    if strip:
        return set(s.strip() for s in sequence)
    else:
        return set(sequence)


def more_than(sequence, number):
    "Returns 1 if sequence has more items than number and 0 if not."
    i = 0
    for item in sequence:
        i += 1
        if i > number:
            return 1
    return 0


def to_term(s, default=None):
    """
    Creates and returns an Identifier of type corresponding
    to the pattern of the given positional argument string ``s``:

    '' returns the ``default`` keyword argument value or ``None``

    '<s>' returns ``URIRef(s)`` (i.e. without angle brackets)

    '"s"' returns ``Literal(s)`` (i.e. without doublequotes)

    '_s' returns ``BNode(s)`` (i.e. without leading underscore)

    """
    if not s:
        return default
    elif s.startswith("<") and s.endswith(">"):
        return URIRef(s[1:-1])
    elif s.startswith('"') and s.endswith('"'):
        return Literal(s[1:-1])
    elif s.startswith("_"):
        return BNode(s)
    else:
        msg = "Unrecognised term syntax: '%s'" % s
        raise Exception(msg)


def from_n3(s, default=None, backend=None, nsm=None):
    r'''
    Creates the Identifier corresponding to the given n3 string.

        >>> from_n3('<http://ex.com/foo>') == URIRef('http://ex.com/foo')
        True
        >>> from_n3('"foo"@de') == Literal('foo', lang='de')
        True
        >>> from_n3('"""multi\nline\nstring"""@en') == Literal(
        ...     'multi\nline\nstring', lang='en')
        True
        >>> from_n3('42') == Literal(42)
        True
        >>> from_n3(Literal(42).n3()) == Literal(42)
        True
        >>> from_n3('"42"^^xsd:integer') == Literal(42)
        True
        >>> from rdflib import RDFS
        >>> from_n3('rdfs:label') == RDFS['label']
        True
        >>> nsm = NamespaceManager(Graph())
        >>> nsm.bind('dbpedia', 'http://dbpedia.org/resource/')
        >>> berlin = URIRef('http://dbpedia.org/resource/Berlin')
        >>> from_n3('dbpedia:Berlin', nsm=nsm) == berlin
        True

    '''
    if not s:
        return default
    if s.startswith('<'):
        return URIRef(s[1:-1])
    elif s.startswith('"'):
        if s.startswith('"""'):
            quotes = '"""'
        else:
            quotes = '"'
        value, rest = s.rsplit(quotes, 1)
        value = value[len(quotes):]  # strip leading quotes
        datatype = None
        language = None

        # as a given datatype overrules lang-tag check for it first
        dtoffset = rest.rfind('^^')
        if dtoffset >= 0:
            # found a datatype
            # datatype has to come after lang-tag so ignore everything before
            # see: http://www.w3.org/TR/2011/WD-turtle-20110809/
            # #prod-turtle2-RDFLiteral
            datatype = from_n3(rest[dtoffset + 2:], default, backend, nsm)
        else:
            if rest.startswith("@"):
                language = rest[1:]  # strip leading at sign

        value = value.replace(r'\"', '"').replace('\\\\', '\\')
        # Hack: this should correctly handle strings with either native unicode
        # characters, or \u1234 unicode escapes.
        value = value.encode("raw-unicode-escape").decode("unicode-escape")
        return Literal(value, language, datatype)
    elif s == 'true' or s == 'false':
        return Literal(s == 'true')
    elif s.isdigit():
        return Literal(int(s))
    elif s.startswith('{'):
        identifier = from_n3(s[1:-1])
        return QuotedGraph(backend, identifier)
    elif s.startswith('['):
        identifier = from_n3(s[1:-1])
        return Graph(backend, identifier)
    elif s.startswith("_:"):
        return BNode(s[2:])
    elif ':' in s:
        if nsm is None:
            # instantiate default NamespaceManager and rely on its defaults
            nsm = NamespaceManager(Graph())
        prefix, last_part = s.split(':', 1)
        ns = dict(nsm.namespaces())[prefix]
        return Namespace(ns)[last_part]
    else:
        return BNode(s)


def check_context(c):
    if not (isinstance(c, URIRef) or
            isinstance(c, BNode)):
        raise ContextTypeError("%s:%s" % (c, type(c)))


def check_subject(s):
    """ Test that s is a valid subject identifier."""
    if not (isinstance(s, URIRef) or isinstance(s, BNode)):
        raise SubjectTypeError(s)


def check_predicate(p):
    """ Test that p is a valid predicate identifier."""
    if not isinstance(p, URIRef):
        raise PredicateTypeError(p)


def check_object(o):
    """ Test that o is a valid object identifier."""
    if not (isinstance(o, URIRef) or
            isinstance(o, Literal) or
            isinstance(o, BNode)):
        raise ObjectTypeError(o)


def check_statement(triple):
    (s, p, o) = triple
    if not (isinstance(s, URIRef) or isinstance(s, BNode)):
        raise SubjectTypeError(s)

    if not isinstance(p, URIRef):
        raise PredicateTypeError(p)

    if not (isinstance(o, URIRef) or
            isinstance(o, Literal) or
            isinstance(o, BNode)):
        raise ObjectTypeError(o)


def check_pattern(triple):
    (s, p, o) = triple
    if s and not (isinstance(s, URIRef) or isinstance(s, BNode)):
        raise SubjectTypeError(s)

    if p and not isinstance(p, URIRef):
        raise PredicateTypeError(p)

    if o and not (isinstance(o, URIRef) or
                  isinstance(o, Literal) or
                  isinstance(o, BNode)):
        raise ObjectTypeError(o)


def date_time(t=None, local_time_zone=False):
    """http://www.w3.org/TR/NOTE-datetime ex: 1997-07-16T19:20:30Z

    >>> date_time(1126482850)
    '2005-09-11T23:54:10Z'

    @@ this will change depending on where it is run
    #>>> date_time(1126482850, local_time_zone=True)
    #'2005-09-11T19:54:10-04:00'

    >>> date_time(1)
    '1970-01-01T00:00:01Z'

    >>> date_time(0)
    '1970-01-01T00:00:00Z'
    """
    if t is None:
        t = time()

    if local_time_zone:
        time_tuple = localtime(t)
        if time_tuple[8]:
            tz_mins = altzone // 60
        else:
            tz_mins = timezone // 60
        tzd = "-%02d:%02d" % (tz_mins // 60, tz_mins % 60)
    else:
        time_tuple = gmtime(t)
        tzd = "Z"

    year, month, day, hh, mm, ss, wd, y, z = time_tuple
    s = "%0004d-%02d-%02dT%02d:%02d:%02d%s" % (
        year, month, day, hh, mm, ss, tzd)
    return s


def parse_date_time(val):
    """always returns seconds in UTC

    # tests are written like this to make any errors easier to understand
    >>> parse_date_time('2005-09-11T23:54:10Z') - 1126482850.0
    0.0

    >>> parse_date_time('2005-09-11T16:54:10-07:00') - 1126482850.0
    0.0

    >>> parse_date_time('1970-01-01T00:00:01Z') - 1.0
    0.0

    >>> parse_date_time('1970-01-01T00:00:00Z') - 0.0
    0.0
    >>> parse_date_time("2005-09-05T10:42:00") - 1125916920.0
    0.0
    """

    if "T" not in val:
        val += "T00:00:00Z"

    ymd, time = val.split("T")
    hms, tz_str = time[0:8], time[8:]

    if not tz_str or tz_str == "Z":
        time = time[:-1]
        tz_offset = 0
    else:
        signed_hrs = int(tz_str[:3])
        mins = int(tz_str[4:6])
        secs = (sign(signed_hrs) * mins + signed_hrs * 60) * 60
        tz_offset = -secs

    year, month, day = ymd.split("-")
    hour, minute, second = hms.split(":")

    t = timegm((int(year), int(month), int(day), int(hour),
                int(minute), int(second), 0, 0, 0))
    t = t + tz_offset
    return t





SUFFIX_FORMAT_MAP = {
    'rdf': 'xml',
    'rdfs': 'xml',
    'owl': 'xml',
    'n3': 'n3',
    'ttl': 'turtle',
    'nt': 'nt',
    'trix': 'trix',
    'xhtml': 'rdfa',
    'html': 'rdfa',
    'svg': 'rdfa',
    'nq': 'nquads',
    'trig': 'trig'
}


def guess_format(fpath, fmap=None):
    """
    Guess RDF serialization based on file suffix. Uses
    ``SUFFIX_FORMAT_MAP`` unless ``fmap`` is provided. Examples:

        >>> guess_format('path/to/file.rdf')
        'xml'
        >>> guess_format('path/to/file.owl')
        'xml'
        >>> guess_format('path/to/file.ttl')
        'turtle'
        >>> guess_format('path/to/file.xhtml')
        'rdfa'
        >>> guess_format('path/to/file.svg')
        'rdfa'
        >>> guess_format('path/to/file.xhtml', {'xhtml': 'grddl'})
        'grddl'

    This also works with just the suffixes, with or without leading dot, and
    regardless of letter case::

        >>> guess_format('.rdf')
        'xml'
        >>> guess_format('rdf')
        'xml'
        >>> guess_format('RDF')
        'xml'
    """
    fmap = fmap or SUFFIX_FORMAT_MAP
    return fmap.get(_get_ext(fpath)) or fmap.get(fpath.lower())


def _get_ext(fpath, lower=True):
    """
    Gets the file extension from a file(path); stripped of leading '.' and in
    lower case. Examples:

        >>> _get_ext("path/to/file.txt")
        'txt'
        >>> _get_ext("OTHER.PDF")
        'pdf'
        >>> _get_ext("noext")
        ''
        >>> _get_ext(".rdf")
        'rdf'
    """
    ext = splitext(fpath)[-1]
    if ext == '' and fpath.startswith("."):
        ext = fpath
    if lower:
        ext = ext.lower()
    if ext.startswith('.'):
        ext = ext[1:]
    return ext


def find_roots(graph, prop, roots=None):
    """
    Find the roots in some sort of transitive hierarchy.

    find_roots(graph, rdflib.RDFS.subClassOf)
    will return a set of all roots of the sub-class hierarchy

    Assumes triple of the form (child, prop, parent), i.e. the direction of
    RDFS.subClassOf or SKOS.broader

    """

    non_roots = set()
    if roots is None:
        roots = set()
    for x, y in graph.subject_objects(prop):
        non_roots.add(x)
        if x in roots:
            roots.remove(x)
        if y not in non_roots:
            roots.add(y)
    return roots


def get_tree(graph,
             root,
             prop,
             mapper=lambda x: x,
             sortkey=None,
             done=None,
             dir='down'):
    """
    Return a nested list/tuple structure representing the tree
    built by the transitive property given, starting from the root given

    i.e.

    get_tree(graph,
       rdflib.URIRef("http://xmlns.com/foaf/0.1/Person"),
       rdflib.RDFS.subClassOf)

    will return the structure for the subClassTree below person.

    dir='down' assumes triple of the form (child, prop, parent),
    i.e. the direction of RDFS.subClassOf or SKOS.broader
    Any other dir traverses in the other direction

    """

    if done is None:
        done = set()
    if root in done:
        return
    done.add(root)
    tree = []

    if dir == 'down':
        branches = graph.subjects(prop, root)
    else:
        branches = graph.objects(root, prop)

    for branch in branches:
        t = get_tree(graph, branch, prop, mapper, sortkey, done, dir)
        if t:
            tree.append(t)

    return (mapper(root), sorted(tree, key=sortkey))




def test():
    import doctest
    doctest.testmod()

if __name__ == "__main__":
    # try to make the tests work outside of the time zone they were written in
    # import os, time
    # os.environ['TZ'] = 'US/Pacific'
    # try:
    #    time.tzset()
    # except AttributeError, e:
    #    print e
        # pass
        # tzset missing! see
        # http://mail.python.org/pipermail/python-dev/2003-April/034480.html
    test()  # pragma: no cover