Solution

Use this snippet to dynamically fetch a validation method from Django's suite of "localflavor" form fields using the ISO 3166-1 two character country code.

def get_postcode_validator(country_code):
    # Django 1.3 uses 'UK' instead of GB - this changes in 1.4
    if country_code == 'GB':
        country_code = 'UK'
    module_path = 'django.contrib.localflavor.%s' % country_code.lower()
    try:
        module = __import__(module_path, fromlist=['forms'])
    except ImportError:
        # No forms module for this country
        return lambda x: x

    fieldname_variants = ['%sPostcodeField',
                          '%sPostCodeField',
                          '%sPostalCodeField',
                          '%sZipCodeField',]
    for variant in fieldname_variants:
        fieldname = variant % country_code.upper()
        if hasattr(module.forms, fieldname):
            return getattr(module.forms, fieldname)().clean
    return lambda x: x

As these validators are from forms, they will raise django.forms.ValidationError if the passed postcode is invalid. Hence your client code should look something like:

from django.forms import ValidationError

def is_postcode_valid(postcode, country_code):
    try:
        get_postcode_validator(country_code)(postcode)
    except ValidationError:
        return False
    return True