# Basics

#### Comments

Comments in Python start with a `#`. There isn't a "true" mutli-line comment like `/**/` in JavaScript.

```python
# This is a comment
# You need multi-line comments?
# Start each line with hash
```

~~haiku~~

#### Primitive Data Types

Python has four primitive data types

* String
* Integer
* Float
* Boolean

```python
type('spam, spam, and spam')
type(3)
type(3.14)
type(True)
type(False)

isinstance('spam, spam, and spam', str)
isinstance(3, int)
isinstance(3.14, float)
isinstance(True, bool)
```

Everything is an object in Python

```python
isinstance('spam, spam, and spam', object)
isinstance(3, object)
isinstance(3.14, object)
isinstance(True, object)
```

#### Variables

To define a variable in Python, type

```python
eggs_ive_eaten = 3
print(eggs_ive_eaten)
```

In Python, variable names:

* must start with a letter or underscore
* cannot start with a number
* contains only alpha-numeric characters and underscors
* are case-sensitive

*NOTE:* The convention for multi-word variable names in Python is snake\_case

Variables can be reassigned

```python
eggs_ive_eaten = 4
print(eggs_ive_eaten)
```

Unlike JavaScript, you cannot declare a variable without initialising it with a value. The closest equivalent would be assigning `None`

```js
let spam
console.log(spam) // -> undefined
```

```python
spam = None
print(spam) # -> None
```

#### String Operators

|     |               |
| --- | ------------- |
| `+` | Concatenation |
| `*` | Replication   |

```python
print('spam, ' * 3 + 'and eggs')
```

#### Arithmetic Operators

|      |                  |
| ---- | ---------------- |
| `+`  | Addition         |
| `-`  | Subtraction      |
| `*`  | Multiplication   |
| `/`  | Division         |
| `//` | Integer Division |
| `%`  | Modulus          |
| `**` | Exponent         |

```python
print(4 + 2 * 3)   # -> 10
print((4 + 2) * 3) # -> 18

print(7 / 3)       # -> 2.3333333333333335
print(7 // 3)      # -> 2

print(4 ** 3)      # -> 64
```

#### Compound Assignment Operators

|       |              | equivalent to      |
| ----- | ------------ | ------------------ |
| `+=`  | `eggs += 2`  | `eggs = eggs + 2`  |
| `-=`  | `eggs -= 2`  | `eggs = eggs - 2`  |
| `*=`  | `eggs *= 2`  | `eggs = eggs * 2`  |
| `/=`  | `eggs /= 2`  | `eggs = eggs / 2`  |
| `//=` | `eggs //= 3` | `eggs = eggs // 2` |
| `%=`  | `eggs %= 2`  | `eggs = eggs % 2`  |
| `**=` | `eggs **= 2` | `eggs = eggs ** 2` |

#### Relational/Comparison Operators

|      |                          |
| ---- | ------------------------ |
| `==` | Equal to                 |
| `!=` | Not equal to             |
| `<`  | Less than                |
| `>`  | Greater than             |
| `<=` | Less than or equal to    |
| `>=` | Greater than or equal to |

```python
print(42 == 42)         # -> True
print(42 == 42.0)       # -> False
print('spam' == 'Spam') # -> False
print('spam' != 'Spam') # -> True
print(42 == '42')       # -> False
```

In Python, you can "chain" conditions

```python
n = 3
print(1 < n < 5) # -> True
```

#### Logical Operators

|       |
| ----- |
| `and` |
| `or`  |
| `not` |

```python
n = '3'
print(1 < n < 5)                      # -> TypeError
print(type(n) == 'int' and 1 < n < 5) # -> False
```


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