PPOL564 | Data Science I - Foundations Data Types in Python

# PPOL564 | Data Science I - Foundations Data Types in Python 
###  Prof. Eric Dunford  ◆  Georgetown University  ◆  McCourt School of Public Policy  ◆  <a href="mailto:eric.dunford@georgetown.edu" class="email">eric.dunford@georgetown.edu</a>

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<div class="slide-footer"> 
PPOL564 | Data Science I - Foundations

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Class 4

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Data Types in Python

</div>

---
class: outline

# Outline for Today

- **_Objects_**

- Cover the **_standard data types_** in Python

- **_Mutable_** vs. _**Immutable_** data types

- **_Copies_**

- Modules

- **Manipulating _Mutable_ Data Structures** (see other notebook)
 
- See supplement notebook for a more detailed look at the functionality of **_strings and dates_**.

---

# Objects

---

# Objects

- `=` assignment operator.

- An objects "type" is defined at runtime; also known as "ducktyping"
  - differs from other languages where type must be made explicit; Python is a dynamically typed language.
  - type cannot be changed once established.
  - An objects class provides a blueprint for object behavior and function.
  
- reference is assigned to an object (e.g. below,  `x` references the object `4` in the statement `x = 4`)

- there can be multiple references to the same object (more on this below)

- objects are assigned a unique object id when initiated.

---

# Objects

![:space 5]

```python
x = 4
x
```

```
## 4
```

```python
type(x)
```

```
## <class 'int'>
```

```python
id(x) # Identity of the object
```

```
## 4477832288
```

---

# Objects

Instantiate objects upon assignment.

```python
x = 4
```

The class defines how the object behaves to different opertions. We use the pointer `.` to access an objects methods.

```python
x.
  |
  V
   __add__()  # method dictating behavior to the `+` operator 
   __mult__() # method dictating behavior to the `*` operator 
   __mod__()  # method dictating behavior to the `%` operator 
   __eq__()   # method dictating behavior to the `==` operator 
     .
     .
     .
```

---

# Objects

Instantiate objects upon assignment.

```python
x = [1,2,3,4]
```

Data classes provide a blueprint for object behavior and functionality (methods).

```python
x.
  |
  V
   append()  # method for appending entries 
   clear()   # method clearing all values from object instance 
   copy()    # method for creating a shallow copy 
   sort()    # method sorting values 
   pop()     # method for removing values for use
   reverse() # method sorting values in reverse
     .
     .
     .
```

---

# Data Types

---

# Data Types

![:space 10]

**_Two ways of instanitating a data class in Python_**

![:space 5]

1. **Literals**: syntatic representation in Python, e.g. `[]`

2. **Constructors**: class constructor, e.g. `list()`

---

# Scalar Data Types

---

## `int` type

`int` literal

```python
x = 1
type(x)
```

```
## <class 'int'>
```

`int` constructor

```python
int(3.4)
```

```
## 3
```

```python
dir(x)
```

```
## ['__abs__', '__add__', '__and__', '__bool__', '__ceil__', '__class__', '__delattr__', '__dir__', '__divmod__', '__doc__', '__eq__', '__float__', '__floor__', '__floordiv__', '__format__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__init__', '__init_subclass__', '__int__', '__invert__', '__le__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__round__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'bit_length', 'conjugate', 'denominator', 'from_bytes', 'imag', 'numerator', 'real', 'to_bytes']
```

---

## `float` type

`float` literal

```python
x = 1.0
type(x)
```

```
## <class 'float'>
```

`float` constructor

```python
float(3)
```

```
## 3.0
```

```python
dir(x)
```

```
## ['__abs__', '__add__', '__bool__', '__class__', '__delattr__', '__dir__', '__divmod__', '__doc__', '__eq__', '__float__', '__floordiv__', '__format__', '__ge__', '__getattribute__', '__getformat__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__int__', '__le__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__pos__', '__pow__', '__radd__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rmod__', '__rmul__', '__round__', '__rpow__', '__rsub__', '__rtruediv__', '__set_format__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', 'as_integer_ratio', 'conjugate', 'fromhex', 'hex', 'imag', 'is_integer', 'real']
```

---

## `bool` type

`float` literal

```python
x = True
type(x)
```

```
## <class 'bool'>
```

`bool` constructor

```python
bool(0)
```

```
## False
```

```python
dir(x)
```

---

## `None` type

`None` literal

```python
x = None
type(x)
```

```
## <class 'NoneType'>
```

```python
dir(x)
```

```
## ['__bool__', '__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']
```

```python
x is None
```

```
## True
```

---

# Collection Data Types

![:space 10]

.center[
|  Type   |  Description  | Example | Mutable | 
|:------:|:------:|:------:|:------:|
| `list` | heterogeneous sequences of objects | `[1,2,3]` | &#10003; |
| `str`  | sequences of characters | `"A word"` | &#10008; |
| `dicts`|  associative array of key/value mappings | `{"a": 1}`| keys &#10008; values  &#10003;
| `sets` | unordered collection of _distinct_ objects | `{1,2,3}` | &#10003; |
|`tuples`| heterogeneous sequence | `(1,2)` | &#10008; | 
]

![:space 2]

We can access the information contained within python collection types using a 0-based index if the container contains an `.index()` method

---

## `list` type

Allows for heterogeneous membership in the various object types

`list` literal

```python
x = [1, 2.2, "str", True, None] 
type(x)
```

```
## <class 'list'>
```

`list` constructor

```python
x = list("This")
type(x)
```

```
## <class 'list'>
```

---

## `str` type

`str` literal

```python
x = "This is a sentence"
type(x)
```

```
## <class 'str'>
```

`str` constructor

```python
x = str(12345)
type(x)
```

```
## <class 'str'>
```

---

## `dict` type

Associative array of key-value pairs; indexed ("hashed") by the keys

`dict` literal

```python
x = {'a':1,'b':2,'c':-2}
type(x)
```

```
## <class 'dict'>
```

`dict` constructor

```python
x = dict(a = 1,b = 2, c= -2)
type(x)
```

```
## <class 'dict'>
```

---

## `set` type

Unordered collection of unique elements

`set` literal

```python
x = {1,2,-2}
type(x)
```

```
## <class 'set'>
```

`set` constructor

```python
x = set([1,2,-2])
type(x)
```

```
## <class 'set'>
```

---

## `tuple` type

Heterogeneous but immutable collection of other data types.

`tuple` literal

```python
x = (1,2)
type(x)
```

```
## <class 'tuple'>
```

`set` constructor

```python
x = tuple([1,2,-2])
type(x)
```

```
## <class 'tuple'>
```