precis-i18n 1.0.2

Usage

Use the get_profile function to obtain a profile object, then use its enforce method. The enforce method returns a Unicode string.

>>> from precis_i18n import get_profile
>>> username = get_profile('UsernameCaseMapped')
>>> username.enforce('Kevin')
'kevin'
>>> username.enforce('\u212Aevin')
'kevin'
>>> username.enforce('\uFF2Bevin')
'kevin'
>>> username.enforce('\U0001F17Aevin')
Traceback (most recent call last):
    ...
UnicodeEncodeError: 'UsernameCaseMapped' codec can't encode character '\U0001f17a' in position 0: DISALLOWED/symbols

Alternatively, you can use the Python str.encode API. Import the precis_i18n.codec module to register the PRECIS codec names. Now you can use the str.encode method with any Unicode string. The result will be a UTF-8 encoded byte string or a UnicodeEncodeError if the string is disallowed.

>>> import precis_i18n.codec
>>> 'Kevin'.encode('UsernameCasePreserved')
b'Kevin'
>>> '\u212Aevin'.encode('UsernameCasePreserved')
b'Kevin'
>>> '\uFF2Bevin'.encode('UsernameCasePreserved')
b'Kevin'
>>> '\u212Aevin'.encode('UsernameCaseMapped')
b'kevin'
>>> '\uFF2Bevin'.encode('OpaqueString')
b'\xef\xbc\xabevin'
>>> '\U0001F17Aevin'.encode('UsernameCasePreserved')
Traceback (most recent call last):
    ...
UnicodeEncodeError: 'UsernameCasePreserved' codec can't encode character '\U0001f17a' in position 0: DISALLOWED/symbols

Alternative Unicode Versions

The get_profile function uses whatever version of unicodedata is provided by the Python runtime. The Unicode version is usually tied to the major version of the Python runtime. Python 3.7.x uses Unicode 11.0. Python 3.6.x uses Unicode 10.0.

To use an alternative unicodedata implementation, pass the unicodedata keyword argument to get_profile.

For example, you could separately install version 12.0 of the unicodedata2 module from PyPI. Then, pass it to get_profile to retrieve a profile that uses Unicode 12.0.

>> import unicodedata2
>> from precis_i18n import get_profile
>> username = get_profile('UsernameCaseMapped', unicodedata=unicodedata2)
>> username.enforce('Kevin')
'kevin'

Supported Profiles and Codecs

Each PRECIS profile has a corresponding codec name. The CaseMapped variant converts the string to lower case for implementing case-insensitive comparison.

• UsernameCasePreserved

• UsernameCaseMapped

• OpaqueString

• NicknameCasePreserved

• NicknameCaseMapped

The CaseMapped profiles use Unicode ToLower per the latest RFC. Previous verions of this package used Unicode Default Case Folding. There are CaseMapped variants for different case transformations. These profile names are deprecated:

• UsernameCaseMapped:ToLower

• UsernameCaseMapped:CaseFold

• NicknameCaseMapped:ToLower

• NicknameCaseMapped:CaseFold

The PRECIS base string classes are also available as codecs:

• IdentifierClass

• FreeFormClass

Userparts and Space Delimited Usernames

The Username profiles in this implementation do not allow spaces. The Username profiles correspond to the definition of “userparts” in RFC 8265. If you want to allow spaces in your application’s user names, you must split the string first.

def enforce_app_username(name):
    profile = precis_i18n.get_profile('UsernameCasePreserved')
    userparts = [profile.enforce(userpart) for userpart in name.split(' ')]
    return ' '.join(userparts)

Be aware that a username constructed this way can contain bidirectional text in the separate userparts.

Error Messages

A PRECIS profile raises a UnicodeEncodeError exception if a string is disallowed. The reason field specifies the kind of error.