Trafaret Tutorial

trafaret_tutorial.py

def trafaret_tutorial():
    """
    So, you have some structure from wild. Say this will be some JSON over API.
    But you cant change this JSON structure.
    """
    sample_data = {
            'userNameFirst': 'Adam',
            'userNameSecond': 'Smith',
            'userPassword': 'supersecretpassword',
            'userEmail': '[email protected]',
            'userRoles': 'teacher, worker, admin',
        }
    """
    And you will not save this structure like this, actually you want something
    like this
    """
    import hashlib

    desired_data = {
            'name': 'Adam',
            'second_name': 'Smith',
            'password': hashlib.md5('supersecretpassword').hexdigest(),
            'email': '[email protected]',
            'roles': ['teacher', 'worker', 'admin'],
        }

    """
    Ok, so you need to convert it somehow. You will write it simple
    """

    new_data = {
            'name': sample_data['userNameFirst'],
            'second_name': sample_data['userNameSecond'],
            'password': hashlib.md5(sample_data['userPassword']).hexdigest(),
            'email': sample_data['userEmail'],
            'roles': [s.strip() for s in sample_data['userRoles'].split(',')]
        }
    assert new_data == desired_data, 'Uh oh'

    """
    And then you will figure out that you can get much more fields
    and decide to optimize your solution with DRY in mind
    """

    FIELDS = {
            'userNameFirst': 'name',
            'userNameSecond': 'second_name',
            'userEmail': 'email',
        }
    new_data = dict((n2, sample_data[n1]) for n1, n2 in FIELDS.items())
    new_data['roles'] = [s.strip() for s
                         in sample_data['userRoles'].split(',')]
    new_data['password'] = hashlib.md5(sample_data['userPassword']).hexdigest()

    assert new_data == desired_data, 'Uh oh'

    """
    Not so bad, if you have many fields it will save your time. But now you get
    new information - 'userEmail' is optional field.
    And specification added field 'userTitle',
    that must be 'bachelor' if not provided'.
    Lets solve it!
    """
    desired_data['title'] = 'Bachelor'  # Update our test to new reality

    FIELDS = {
            'userNameFirst': 'name',
            'userNameSecond': 'second_name',
            'userEmail': ('email', '__optional'),
            'userTitle': ('title', 'Bachelor'),
        }

    new_data = {}
    for old, new in FIELDS.items():
        if isinstance(new, tuple):
            new, default = new
        if old not in sample_data:
            if default == '__optional':
                continue
            new_data[new] = default
        else:
            new_data[new] = sample_data[old]

    new_data['roles'] = [s.strip() for s
                         in sample_data['userRoles'].split(',')]
    new_data['password'] = hashlib.md5(sample_data['userPassword']).hexdigest()

    assert new_data == desired_data, 'Uh oh'

    """
    Hm, ok, so much code, uh oh.
    I think first variant were more straightforward.
    """
    new_data = {
            'name': sample_data['userNameFirst'],
            'second_name': sample_data['userNameSecond'],
            'password': hashlib.md5(sample_data['userPassword']).hexdigest(),
            'roles': [s.strip() for s in sample_data['userRoles'].split(',')]
        }
    if 'userEmail' in sample_data:
        new_data['email'] = sample_data['userEmail']
    new_data['title'] = sample_data.get('userTitle', 'Bachelor')

    assert new_data == desired_data, 'Uh oh'

    """
    Good old code without complicate smell, good, yeah.
    But what if you will have more fields?
    I mean much more, and what will you do?
    It seems you are ready to make new cool library for this things.

    But wait, I did!
    """
    import trafaret as t

    hash_md5 = lambda d: hashlib.md5(d).hexdigest()
    comma_to_list = lambda d: [s.strip() for s in d.split(',')]

    converter = t.Dict({
        t.Key('userNameFirst') >> 'name': t.String,
        # Bonus: validation with regexp!
        t.Key('userNameSecond') >>
                                'second_name': t.String(regex=r'^[a-zA-Z]+$'),
        # You can bind as many converters as you want
        t.Key('userPassword') >> 'password': t.String >> hash_md5,
        # Bonus: trafaret.Email validates that string is valid email
        t.Key('userEmail', optional=True, to_name='email'): t.Email,
        t.Key('userTitle', default='Bachelor', to_name='title'): t.String,
        t.Key('userRoles', to_name='roles'): t.String >> comma_to_list,
    })

    assert converter.check(sample_data) == desired_data

    sample_data['userNameSecond'] += '123'  # this will raise validation error
    try:
        converter.check(sample_data)
        raise Exception('Validation doesn\'t work!')
    except t.DataError:
        pass

    """
    So go to the https://github.com/Deepwalker/trafaret and start using it!
    """

if __name__ == '__main__':
    trafaret_tutorial()