Python - metody specjalne

class: center, middle

# Python

## Metody specjalne

### 30/11/2018

Paweł Suder

<pasuder@agh.edu.pl>

https://pasuder.github.io/labs/doc/lab01

---

# Agenda

1. Metody specjalne
1. Operatory i funkcje
1. Przykłady
1. Zadania

---

# Metody specjalne

- podstawowe
- dostępu
- porównania
- wywołania
- konteneryzacji
- matematyczne
- `with`

Więcej informacji:

- [Metody specjalne](https://docs.python.org/3.5/reference/datamodel.html#special-method-names)
- [Standardowe typy](https://docs.python.org/3.5/library/stdtypes.html)

---

# Operatory i funkcje

- podstawowe: `A()` 
- dostępu: `a.b` `a.b = c` `del a.b`
- porównania: `a == b` `a != b` `a < b` `a >= b`
- wywołania: `a()`
- konteneryzacji: `a[b]` `a[b] = c` `del a[b]` `for b in a: ...`

Więcej informacji:

- [Operatory](https://docs.python.org/3.5/library/operator.html)
- [Funkcje](https://docs.python.org/3.5/library/functions.html)

---

### Przykłady - podstawowe

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
```

```python
>>> o = Object('anything')
>>> print(o)
<__main__.Object object at 0x7efe9a213470>
>>> o
<__main__.Object object at 0x7efe9a213470>
```

---

### Przykłady - podstawowe

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    def __str__(self):
        return 'Object: %s' % self.__private_field
```

```python
>>> o = Object('anything')
>>> print(o)
Object: anything
>>> o
<__main__.Object object at 0x7efe9a213748>
```

---

### Przykłady - podstawowe

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    def __str__(self):
        return 'Object: %s' % self.__private_field
    def __repr__(self):
        return '<Object: __private_field=%s>' % self.__private_field
```

```python
>>> o = Object('anything')
>>> print(o)
Object: anything
>>> o
<Object: __private_field=anything>
```

---

### Przykłady - podstawowe

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    ...
    def __hash__(self):
        return hash(self.__private_field)
```

```python
>>> a = Object('first')
>>> b = Object('second')
>>> hash(a), hash(b)
(1666425883664241038, -9168246016793942683)
>>> c = Object('first')
>>> hash(c)
1666425883664241038
>>> hex(id(a)), hex(id(c))
('0x7efe9a213d68', '0x7efe9a213160')
```

---

### Przykłady - podstawowe

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    ...
    def __bool__(self):
        return bool(self.__private_field)
```

```python
>>> o = Object('false')
>>> o
<Object: __private_field=false>
>>> bool(o)
True
>>> o == True, o == False
(False, False)
>>> o is True, o is False
(False, False)
```

---

### Przykłady - podstawowe

```python
>>> o = Object('example')
>>> bool(o)
True
>>> o = Object('')
>>> bool(o)
False
>>> o = Object(0)
>>> bool(o)
False
>>> o = Object(1)
>>> bool(o)
True
```

---

### Przykłady - dostępu

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    ...
    def __getattr__(self, name):
        return self.__private_field.get(name)
```

```python
>>> o = Object({'a': 1, 'b': '2', 'c': object()})
>>> o
<Object: __private_field={'a': 1, 'b': '2', 'c': <object object at 0x7efe9aa2c0d0>}>
>>> o.a
1
>>> o.a, o.b
(1, '2')
>>> o.a, o.b, o.c
(1, '2', <object object at 0x7efe9aa2c0d0>)
```

---

### Przykłady - dostępu

```python
class DynamicObject(object):
    __fields = dict()
    def __repr__(self):
        return '<Object: fields=%s>' % self.__fields
    def __getattr__(self, name):
        return self.__fields.get(name)
    def __setattr__(self, name, value):
        self.__fields[name] = value
```

```python
>>> o = DynamicObject()
>>> o
<Object: fields={}>
>>> o.blah = 'tests'
>>> o
<Object: fields={'blah': 'tests'}>
>>> o.blah
'tests'

```

---

### Przykłady - dostępu

```python
class DynamicObject(object):
    __fields = dict()
    ...
    def __delattr__(self, name):
        del self.__fields[name]
```

```python
>>> o = DynamicObject()
>>> o.blah = 'tests'
>>> o.blah
'tests'
>>> del o.blah
>>> o.blah
>>> o
<Object: fields={}>

```

---

### Przykłady - porównania

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    ...
    def __eq__(self, other):
        return self.__private_field == other.__private_field
```

```python
>>> a = Object('first'); b = Object('second')
>>> a == b
False
>>> a != b
True
>>> c = Object('first')
>>> a == c
True
```

---

### Przykłady - porównania

```python
class Object(object):
    def __init__(self, param):
        self.__private_field = param
    ...
    def __ne__(self, other):
        return True
```

```python
>>> a = Object('first'); b = Object('second')
>>> a == b
False
>>> a != b
True
>>> c = Object('first')
>>> a == c
True
>>> a != c
True
```

---

### Przykłady - porównania

```python
class Object(object):
    ...
    def __lt__(self, other):
        return self.__private_field < other.__private_field
    def __ge__(self, other):
        return not self.__private_field < other.__private_field
```

```python
>>> a = Object(10); b = Object(20); c = Object(10)
>>> a > b, a < b, a <= b, a >= b
(False, True, True, False)
>>> b > a, b < a, b <= a, b >= a
(True, False, False, True)
>>> a > c, a < c, a <= c, a >= c
(False, False, True, True)
>>> c > a, c < a, c <= a, c >= a
(False, False, True, True)

```

---

### Przykłady - wywołania

```python
class CalledObject(object):
    def __init__(self, name):
        self.__name = name
    def __call__(self, *args, **kwargs):
        return 'Called %s with (%s, %s)' % (self.__name, str(args), str(kwargs))
```

```python
>>> c = CalledObject('test')
>>> c()
'Called test with ((), {})'
>>> c(1,2,3)
'Called test with ((1, 2, 3), {})'
>>> c(1,2,3,name='value')
"Called test with ((1, 2, 3), {'name': 'value'})"

```

---