try:

    import cPickle as pickle

except ImportError:

    import pickle



from django.conf import settings

from django.forms import BooleanField

from django.utils.crypto import salted_hmac

from django.utils.hashcompat import md5_constructor





def security_hash(request, form, *args):

    """

    Calculates a security hash for the given Form instance.



    This creates a list of the form field names/values in a deterministic

    order, pickles the result with the SECRET_KEY setting, then takes an md5

    hash of that.

    """

    import warnings

    warnings.warn("security_hash is deprecated; use form_hmac instead",

                  PendingDeprecationWarning)

    data = []

    for bf in form:

        # Get the value from the form data. If the form allows empty or hasn't

        # changed then don't call clean() to avoid trigger validation errors.

        if form.empty_permitted and not form.has_changed():

            value = bf.data or ''

        else:

            value = bf.field.clean(bf.data) or ''

        if isinstance(value, basestring):

            value = value.strip()

        data.append((bf.name, value))

        

    data.extend(args)

    data.append(settings.SECRET_KEY)



    # Use HIGHEST_PROTOCOL because it's the most efficient. It requires

    # Python 2.3, but Django requires 2.4 anyway, so that's OK.

    pickled = pickle.dumps(data, pickle.HIGHEST_PROTOCOL)



    return md5_constructor(pickled).hexdigest()





def form_hmac(form):

    """

    Calculates a security hash for the given Form instance.

    """

    data = []

    for bf in form:

        # Get the value from the form data. If the form allows empty or hasn't

        # changed then don't call clean() to avoid trigger validation errors.

        if form.empty_permitted and not form.has_changed():

            value = bf.data or ''

        else:

            value = bf.field.clean(bf.data) or ''

        if isinstance(value, basestring):

            value = value.strip()

        data.append((bf.name, value))



    pickled = pickle.dumps(data, pickle.HIGHEST_PROTOCOL)

    key_salt = 'django.contrib.formtools'

    return salted_hmac(key_salt, pickled).hexdigest()