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# 2.7v3.5

## Comparisons

#### Strings

|                    2 | 3                        |
| -------------------: | ------------------------ |
| Default 8-bit String | Default unicode          |
|  `u'Hi'` for unicode | `b'Hi'` for 8-bit string |

#### Division

2, truncates by default:

`3/2` => 1

`3.0//2` => 1.0

3, // for truncating

`3.0/2` => 1

`3//2` => 1

#### Iterators 3 vs Lists 2

Optimized native functions used iterators in 3 vs lists in 2

i.e `range`, `map`, `filter`, `dict.[ft]`, `zip`

#### Print

In 2 can do `print Hello`

In 3, print is a regular ft so must include () `print(Hello)`

**Raw Input in 2.7 s now input in 3**

## 2.7 Specific Stuff

```python
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
```

Import python 3 functionality(good for migration and changes fundamental python props), needs to be near top of code because imported differently and changes things about language

## 3.5 New Features

### Dictionary Comprehensions

`{k: v for k, v in stuff}`

### Iterable Unwrapping

```python
#Python 2
first, rest, last = seq[0], seq[1:-1], seq[-1]
#Python 3
first, *rest, last = seq
```

### Objects

python 3 has different objects or something look it up

### Formatting Print

```python
name = 'World'
program = 'Python'
print(f'Hello {name}! This is {program}')
```

### Typing Hinting

This doesn't make python a staticly typed language suddenly, but basically inline comments

```python
def greeting(name: str) -> str:
    return 'Hello ' + name
```

#### Type Alias

```python
from typing import List
Vector = List[float]

def scale(scalar: float, vector: Vector) -> Vector:
    return [scalar * num for num in vector]

# typechecks; a list of floats qualifies as a Vector.
new_vector = scale(2.0, [1.0, -4.2, 5.4])
```

#### Dataclass

Actually creates a \_\_str and \_\_init for you

```python
from dataclasses import dataclass

@dataclass
class Armor:
    armor: float
    description: str
    level: int = 1

    def power(self) -> float:
        return self.armor * self.level

armor = Armor(5.2, "Common armor.", 2)
armor.power()
# 10.4
print(armor)
```

### Actually Type Checking

Use pycharm or something with this (atom has a mypy plugin)

OR

`pip install mypy`

`mypy [file]`


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