### TUPLES ###

* like lists, but they don't change size
* properties: ordered, iterable, immutable, can contain multiple data types

## create a tuple
```python
digits = (0, 1, 'two')          # create a tuple directly
digits = tuple([0, 1, 'two'])   # create a tuple from a list
zero = (0,)                     # trailing comma is required to indicate it's a tuple
```

## examine a tuple
```python
digits[2]           # returns 'two'
len(digits)         # returns 3
digits.count(0)     # counts the number of instances of that value (1)
digits.index(1)     # returns the index of the first instance of that value (1)
```

## elements of a tuple cannot be modified
```python
digits[2] = 2       # throws an error
```

## concatenate tuples
```python
digits = digits + (3, 4)
```

## create a single tuple with elements repeated (also works with lists)
```python
(3, 4) * 2          # returns (3, 4, 3, 4)
```

## sort a list of tuples
```python
tens = [(20, 60), (10, 40), (20, 30)]
sorted(tens)        # sorts by first element in tuple, then second element
                    #   returns [(10, 40), (20, 30), (20, 60)]
```

## tuple unpacking
```python
bart = ('male', 10, 'simpson')  # create a tuple
(sex, age, surname) = bart      # assign three values at once
```python