Lecture 9 — Tuples, Modules, and Images¶

Overview¶

While most of this lecture is not covered in our textbook, this lecture serves as an introduction to using more complex data types that are iterables. WE are familiar with one iterable - string.
We will first learn a simple data type called tuples which allow us to work with multiple values together - including returning two or more values from a function.
We will then revisit modules, how functions you write can be used in other programs.
Most of the class we will be learning how to use a new module for manipulating images.
- We will introduce a new data type - an image - which is much more complex than the other data types we have learned so far.
- We will study a module called pillow which is specifically designed for this data type.

A tuple is a simple data type that puts together multiple values as a single unit.
A tuple allows you to access individual elements: first value starts at zero (this “indexing” will turn into a big Computer Science thing!):
```
>>> x = (4, 5, 10)   # note the parentheses
>>> print(x[0])
4
>>> print(x[2])
10
>>> len(x)
3
```
As we will explore in class tuples and strings are similar in many ways:
```
>>> s = 'abc'
>>> s[0]
'a'
>>> s[1]
'b'
```
Just like strings, you cannot change a part of the tuple; you can only change the entire tuple:

Recall that a module is a collection of Python variables, functions and objects, all stored in a file.
Modules allow code to be shared across many different programs.
Before we can use a module, we need to import it. The import of a module and use of functions within the module have the follow general form:
```
>>> import module_name
>>> module_name.function(arguments)
```

PILLOW is a series of modules built around the Image type, our first object type that is not part of the main Python language.
- We have to tell Python about this type through import.
We will use images as a continuing example of what can be done in programming beyond numbers and beyond text.
See

http://pillow.readthedocs.org/en/latest/handbook/tutorial.html

for more details.