Fluent_python,01-data-model

01-data-model/frenchdeck.py1. When the Python interpreter encounters a special syntax, it uses the special method __ to activate some basic object operations.

The existence of special methods is for the purpose of being interpreted. Without My_object.len (), Len (my_object) should be used.
such as My_collection[key], my_coolection._getitem_(key).
For example, if you implement __len () __ in class Frenchdeck, you can use Len (object).
Implement _GetItem () _ You can use Deck[position].

2. Many times the invocation of the special method __ is implicit

For example, for I in x:-X._iter_(), if __iter__ is implemented in X.

3. Python contains a function random.choice that randomly selects an element from the sequence.

    fromimport choice    = [1,2,3,4,5]    choice(a)

4. Because class Frenchdeck is an iterative __, the __in operator __ can be used on the Frenchdeck class. In addition, if a collection type does not implement the __contains__ method, the in operator does an iterative search sequentially.

>>> Card(‘Q‘‘hearts‘in deckTrue>>> Card(‘Q‘‘beasts‘in deckFalse

01-data-model/vector2d.py5. Use the Special method __abs__ to implement the vector, __add__ implement the ' + ' operator, __mul__ implement ' * ' operator 6. After implementing __repr__

V1 = vector ()
Both print (v1) and repr (v1) can express an object in the form of a string.

7.%s differs from%r,%r output is raw data

%s with Str (). %r use Repr ().
%s to the user,%r for debug.
__REPR__ goal is to be unambiguous
__STR__ goal is to be readable
If an object does not have a __str__ function, the Python interpreter uses __repr__ as an alternative.

fromimport= datetime.today()print(‘%s‘% d)print(‘%r‘% d)

8. BOOL (x) is X._ BOOL (), if no _bool exists() calls __len__ () 9. Special methods List Chinese e-book P57 Summary:

Academic: Python prefers to say data types, which in fact means object models. By implementing a special method of Python data types to provide a rich set of meta-object protocols (the meta-object is the core object for the build language, the protocol means the API to build the core language), the custom type can behave like the built-in content, thus writing more flexible and Pythonic code.

Popularization: By implementing a Special method (_method_), some behaviors and functions of the object can be given.

Fluent_python,01-data-model