api.py

"""
Core classes for validation.
"""

import declarative
import textwrap
import re
import os
try:
    from pkg_resources import resource_filename
except ImportError:
    resource_filename = None

__all__ = ['NoDefault', 'Invalid', 'Validator', 'Identity',
           'FancyValidator', 'is_validator']

import gettext

def get_localedir():
    """
    Retrieve the location of locales.

    If we're built as an egg, we need to find the resource within the egg.
    Otherwise, we need to look for the locales on the filesystem or in the
    system message catalog.
    """
    locale_dir = ''
    # Check the egg first
    if resource_filename is not None:
        try:
            locale_dir = resource_filename(__name__, "/i18n")
        except NotImplementedError:
            # resource_filename doesn't work with non-egg zip files
            pass
    if not hasattr(os, 'access'):
        # This happens on Google App Engine
        return os.path.join(os.path.dirname(__file__), 'i18n')
    if os.access(locale_dir, os.R_OK | os.X_OK):
        # If the resource is present in the egg, use it
        return locale_dir

    # Otherwise, search the filesystem
    locale_dir = os.path.join(os.path.dirname(__file__), 'i18n')
    if not os.access(locale_dir, os.R_OK | os.X_OK):
        # Fallback on the system catalog
        locale_dir = os.path.normpath('/usr/share/locale')

    return locale_dir

def set_stdtranslation(domain="FormEncode", languages=None, \
                       localedir = get_localedir()):

    t = gettext.translation(domain=domain, \
                            languages=languages, \
                            localedir=localedir, fallback=True)
    global _stdtrans
    _stdtrans = t.ugettext

set_stdtranslation()

def _(s): return s # dummy i18n translation function, nothing is translated here.
                   # Instead this is actually done in api.Validator.message.
                   # The surrounding _("string") of the strings is only for extracting
                   # the strings automatically
                   # if you run pygettext with this source comment this function out temporarly 

class NoDefault:
    pass

def is_validator(obj):
    return (isinstance(obj, Validator) or
            (isinstance(obj, type) and
             issubclass(obj, Validator)))

class Invalid(Exception):

    """
    This is raised in response to invalid input.  It has several
    public attributes:

    msg:
        The message, *without* values substituted.  For instance, if
        you want HTML quoting of values, you can apply that.
    substituteArgs:
        The arguments (a dictionary) to go with `msg`.
    str(self):
        The message describing the error, with values substituted.
    value:
        The offending (invalid) value.
    state:
        The state that went with this validator.  This is an
        application-specific object.
    error_list:
        If this was a compound validator that takes a repeating value,
        and sub-validator(s) had errors, then this is a list of those
        exceptions.  The list will be the same length as the number of
        values -- valid values will have None instead of an exception.
    error_dict:
        Like `error_list`, but for dictionary compound validators.
    """

    def __init__(self, msg,
                 value, state, error_list=None, error_dict=None):
        Exception.__init__(self, msg)
        self.msg = msg
        self.value = value
        self.state = state
        self.error_list = error_list
        self.error_dict = error_dict
        assert (not self.error_list or not self.error_dict), (
                "Errors shouldn't have both error dicts and lists "
                "(error %s has %s and %s)"
                % (self, self.error_list, self.error_dict))

    def __str__(self):
        val = self.msg
        #if self.value:
        #    val += " (value: %s)" % repr(self.value)
        return val    

    def __unicode__(self):
        if isinstance(self.msg, unicode):
            return self.msg
        elif isinstance(self.msg, str):
            return self.msg.decode('utf8')
        else:
            return unicode(self.msg)

    def unpack_errors(self, encode_variables=False, dict_char='.',
                      list_char='-'):
        """
        Returns the error as a simple data structure -- lists,
        dictionaries, and strings.
        
        If ``encode_variables`` is true, then this will return a flat
        dictionary, encoded with variable_encode
        """
        if self.error_list:
            assert not encode_variables, (
                "You can only encode dictionary errors")
            assert not self.error_dict
            result = []
            for item in self.error_list:
                if not item:
                    result.append(item)
                else:
                    result.append(item.unpack_errors())
            return result
        elif self.error_dict:
            result = {}
            for name, item in self.error_dict.items():
                if isinstance(item, (str, unicode)):
                    result[name] = item
                else:
                    result[name] = item.unpack_errors()
            if encode_variables:
                import variabledecode
                result = variabledecode.variable_encode(result, add_repetitions=False,
                                                        dict_char=dict_char,
                                                        list_char=list_char)
                for key in result.keys():
                    if not result[key]:
                        del result[key]
            return result
        else:
            assert not encode_variables, (
                "You can only encode dictionary errors")
            return self.msg


############################################################
## Base Classes
############################################################

class Validator(declarative.Declarative):

    """
    The base class of most validators.  See `IValidator` for more, and
    `FancyValidator` for the more common (and more featureful) class.
    """

    _messages = {}
    if_missing = NoDefault
    repeating = False
    compound = False
    gettextargs = {}
    use_builtins_gettext = True #In case you dont want to use __builtins__._
                                #altough it may be definied, set this to False
    
    __singletonmethods__ = ('to_python', 'from_python', 'message', 'all_messages',
                            'subvalidators')

    def __classinit__(cls, new_attrs):
        if new_attrs.has_key('messages'):
            cls._messages = cls._messages.copy()
            cls._messages.update(cls.messages)
            del cls.messages
        cls._initialize_docstring()

    def __init__(self, *args, **kw):
        if kw.has_key('messages'):
            self._messages = self._messages.copy()
            self._messages.update(kw['messages'])
            del kw['messages']
        declarative.Declarative.__init__(self, *args, **kw)

    def to_python(self, value, state=None):
        return value

    def from_python(self, value, state=None):
        return value

    def message(self, msgName, state, **kw):
        #determine translation function
        try:
            trans = state._
        except AttributeError:
            try:
                if self.use_builtins_gettext:
                    import __builtin__
                    trans = __builtin__._
                    
                else:
                    trans = _stdtrans
 
            except AttributeError:
                trans = _stdtrans
 
        if not callable(trans):
            trans = _stdtrans


        msg = self._messages[msgName]
        msg = trans(msg, **self.gettextargs)
        try:
            return msg % kw
        except KeyError, e:
            raise KeyError(
                "Key not found (%s) for %r=%r %% %r (from: %s)"
                % (e, msgName, self._messages.get(msgName), kw,
                   ', '.join(self._messages.keys())))

    def all_messages(self):
        """
        Return a dictionary of all the messages of this validator, and
        any subvalidators if present.  Keys are message names, values
        may be a message or list of messages.  This is really just
        intended for documentation purposes, to show someone all the
        messages that a validator or compound validator (like Schemas)
        can produce.

        @@: Should this produce a more structured set of messages, so
        that messages could be unpacked into a rendered form to see
        the placement of all the messages?  Well, probably so.
        """
        msgs = self._messages.copy()
        for v in self.subvalidators():
            inner = v.all_messages()
            for key, msg in inner:
                if key in msgs:
                    if msgs[key] == msg:
                        continue
                    if isinstance(msgs[key], list):
                        msgs[key].append(msg)
                    else:
                        msgs[key] = [msgs[key], msg]
                else:
                    msgs[key] = msg
        return msgs

    def subvalidators(self):
        """
        Return any validators that this validator contains.  This is
        not useful for functional, except to inspect what values are
        available.  Specifically the ``.all_messages()`` method uses
        this to accumulate all possible messages.
        """
        return []

    #@classmethod
    def _initialize_docstring(cls):
        """
        This changes the class's docstring to include information
        about all the messages this validator uses.
        """
        doc = cls.__doc__ or ''
        doc = [textwrap.dedent(doc).rstrip()]
        messages = cls._messages.items()
        messages.sort()
        doc.append('\n\n**Messages**\n\n')
        for name, default in messages:
            default = re.sub(r'(%\(.*?\)[rsifcx])', r'``\1``', default)
            doc.append('``'+name+'``:\n')
            doc.append('  '+default+'\n\n')
        cls.__doc__ = ''.join(doc)
    _initialize_docstring = classmethod(_initialize_docstring)

class _Identity(Validator):
    def __repr__(self):
        return 'validators.Identity'
Identity = _Identity()

class FancyValidator(Validator):

    """
    FancyValidator is the (abstract) superclass for various validators
    and converters.  A subclass can validate, convert, or do both.
    There is no formal distinction made here.

    Validators have two important external methods:
    
    * .to_python(value, state):
      Attempts to convert the value.  If there is a problem, or the
      value is not valid, an Invalid exception is raised.  The
      argument for this exception is the (potentially HTML-formatted)
      error message to give the user.

    * .from_python(value, state):
      Reverses to_python.

    There are five important methods for subclasses to override,
    however none of these *have* to be overridden, only the ones that
    are appropriate for the validator:
    
    * __init__():
      if the `declarative.Declarative` model doesn't work for this.

    * .validate_python(value, state):
      This should raise an error if necessary.  The value is a Python
      object, either the result of to_python, or the input to
      from_python.

    * .validate_other(value, state):
      Validates the source, before to_python, or after from_python.
      It's more common to use `.validate_python()` however.

    * ._to_python(value, state):
      This returns the converted value, or raises an Invalid
      exception if there is an error.  The argument to this exception
      should be the error message.

    * ._from_python(value, state):
      Should undo .to_python() in some reasonable way, returning
      a string.

    Validators should have no internal state besides the
    values given at instantiation.  They should be reusable and
    reentrant.

    All subclasses can take the arguments/instance variables:
    
    * if_empty:
      If set, then this value will be returned if the input evaluates
      to false (empty list, empty string, None, etc), but not the 0 or
      False objects.  This only applies to ``.to_python()``.
      
    * not_empty:
      If true, then if an empty value is given raise an error.
      (Both with ``.to_python()`` and also ``.from_python()``
      if ``.validate_python`` is true).

    * strip:
      If true and the input is a string, strip it (occurs before empty
      tests).

    * if_invalid:
      If set, then when this validator would raise Invalid during
      ``.to_python()``, instead return this value.
      
    * if_invalid_python:
      If set, when the Python value (converted with
      ``.from_python()``) is invalid, this value will be returned.

    * accept_python:
      If True (the default), then ``.validate_python()`` and
      ``.validate_other()`` will not be called when
      ``.from_python()`` is used.
    """

    if_invalid = NoDefault
    if_invalid_python = NoDefault
    if_empty = NoDefault
    not_empty = False
    accept_python = True
    strip = False

    messages = {
        'empty': _("Please enter a value"),
        'badType': _("The input must be a string (not a %(type)s: %(value)r)"),
        'noneType': _("The input must be a string (not None)"),
        }

    def to_python(self, value, state=None):
        try:
            if self.strip and isinstance(value, (str, unicode)):
                value = value.strip()
            elif hasattr(value, 'mixed'):
                # Support Paste's MultiDict
                value = value.mixed()
            if self.is_empty(value):
                if self.not_empty:
                    raise Invalid(self.message('empty', state), value, state)
                else:
                    if self.if_empty is not NoDefault:
                        return self.if_empty
                    else:
                        return self.empty_value(value)
            vo = self.validate_other
            if vo and vo is not self._validate_noop:
                vo(value, state)
            tp = self._to_python
            if tp:
                value = tp(value, state)
            vp = self.validate_python
            if vp and vp is not self._validate_noop:
                vp(value, state)
            return value
        except Invalid:
            if self.if_invalid is NoDefault:
                raise
            else:
                return self.if_invalid

    def from_python(self, value, state=None):
        try:
            if self.strip and isinstance(value, (str, unicode)):
                value = value.strip()
            if not self.accept_python:
                if self.is_empty(value):
                    if self.not_empty:
                        raise Invalid(self.message('empty', state),
                                      value, state)
                    else:
                        return self.empty_value(value)
                vp = self.validate_python
                if vp and vp is not self._validate_noop:
                    vp(value, state)
                fp = self._from_python
                if fp:
                    value = fp(value, state)
                vo = self.validate_other
                if vo and vo is not self._validate_noop:
                    vo(value, state)
                return value
            else:
                if self.is_empty(value):
                    return self.empty_value(value)
                fp = self._from_python
                if fp:
                    value = self._from_python(value, state)
                return value
        except Invalid:
            if self.if_invalid_python is NoDefault:
                raise
            else:
                return self.if_invalid_python

    def is_empty(self, value):
        # None and '' are "empty"
        return value is None or value == '' or (
            isinstance(value, (list, tuple, dict)) and not value)

    def empty_value(self, value):
        return None

    def assert_string(self, value, state):
        if not isinstance(value, (str, unicode)):
            raise Invalid(self.message('badType', state,
                                       type=type(value), value=value),
                          value, state)

    def base64encode(self, value):
        """
        Encode a string in base64, stripping whitespace and removing
        newlines.
        """
        return value.encode('base64').strip().replace('\n', '')

    def _validate_noop(self, value, state):
        """
        A validation method that doesn't do anything.
        """
        pass
    
    validate_python = validate_other = _validate_noop
    _to_python = None
    _from_python = None