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Wingardium Leviosa

Wingardium Leviosa

Python declarative magic basics

200442040b9d038626d92d408f499642?s=128

Serge Matveenko

April 25, 2014
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  1. «Вингардиум левиоса» Основы декларативной магии Сергей Матвеенко

  2. «Harry Potter and the Philosopher's Stone»

  3. http://xkcd.com/353/

  4. ➢ Описания: существительные и прилагательные, а не глаголы ➢ Независимость

    от реализации ➢ Валидация без компиляции ➢ Не нужно уметь программировать ➢ GUI для редактирования ➢ Потому что это модно :) Декларативное программирование
  5. ➢ Декораторы ➢ Метаклассы ◦ Атрибуты классов ◦ Аргументы классов

    ◦ Аннотации аргументов методов ➢ Import hooks ◦ Модификация AST ◦ Генерация кода ➢ Внешние описания ◦ YAML Декларативность в Python
  6. Декораторы @this_is_decorator(safe_mode=True) def method(arg1, arg2): # we will have just

    a few lines here return arg1 + arg2 @abstractclass class ObjectBase: def foo(self): return NotImplemented
  7. Метаклассы: атрибуты классов class MyClass(ObjectBase): sequence = True sorted =

    False seq = MyClass() seq.extend([3, 2, 5]) print(seq) > [3, 2, 5]
  8. Метаклассы: атрибуты классов class ObjectMeta(type): def __new__(cls, name, bases, attrs):

    type_new = type.__new__(cls, name, bases, attrs) if attrs.get('sequence', False): # add sequence realization if attrs.get('sorted', False): # add sorted realization return type_new class ObjectBase(metaclass=ObjectMeta): pass class MyClass(ObjectBase): sequence = True sorted = False
  9. Метаклассы: аргументы классов class SequenceMeta(type): def __new__(cls, name, bases, attrs,

    sorted=False): type_new = type.__new__(cls, name, bases, attrs) if sorted: # add sorted realization return type_new class SortedSequence(metaclass=SequenceMeta, sorted=True): pass seq = SortedSequence()
  10. Метаклассы: аннотации import inspect class StrictMeta(type): def __new__(cls, name, bases,

    args): type_new = type.__new__(cls, name, bases, args) for attr_name in dir(type_new): method = getattr(type_new.attr_name) if callable(method): parameters = inspect.signature(method).parameters.values() # construct decorated method setattr(new_type, attr_name, method) return new_type class TextNumber(metaclass=StrictMeta): value = "0" def __add__(self, value: r'[\d\.]+'): # add implementation return self.value
  11. Import hooks: модификация AST # smart_sql.py class MyImporter: def load_module(self,

    name): # modify AST return module sys.path_hooks.insert(0, MyImporter) # prog.py import smart_sql query = ( id, Point(x, y) for id, x, y in "sql_table_name" if len([(x0, y0), (x, y)]) < 3)
  12. Import hooks: генерация кода # smart_sql.py class MyImporter: def find_module(self,

    fullname, path=None): # find path to DSL source file self.path = path return self def load_module(self, name): # generate and compile python module from DSL return module sys.meta_path.insert(0, MyImporter) # prog.py import smart_sql from dsl_queries import query result = query.find(radius)
  13. YAML # pytest-yamlwsgi test_index: - path: / assert_status: 200 assert_contains:

    Hello - path: / assert_contains: Hello - path: / assert_status: 200
  14. Django ORM from django.db import models class Musician(models.Model): first_name =

    models.CharField(max_length=50) last_name = models.CharField(max_length=50) instrument = models.CharField(max_length=100) class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) release_date = models.DateField() num_stars = models.IntegerField()
  15. Django class-based generic views class PublisherDetail(DetailView): context_object_name = 'publisher' queryset

    = Publisher.objects.all() class BookList(ListView): queryset = Book.objects.order_by('-publication_date') context_object_name = 'book_list' class AcmeBookList(ListView): context_object_name = 'book_list' queryset = Book.objects.filter(publisher__name='Acme') template_name = 'books/acme_list.html'
  16. Function annotations # http://code.activestate.com/recipes/578528/ @typecheck def happy1(a:int, b:list, c:tuple=(1,2,3)) ->

    float: return 3.14 @typecheck def happy_wo_annotation(a:int, b, c:tuple=(1,2,3)) -> float: return 3.14 @typecheck def unhappy1(a:int, b:str) -> float: return 314 # This can never succeed in return type
  17. Вопросы? github.com/lig ptsecurity.com