Boston Python Workshop 4/Twitter handout

Twitter goals

 * practice for loops
 * practice using functions
 * practice implementing functions
 * see what it's like to use an API
 * have fun collecting data from Twitter

Indentation reminder
In Python, indentation matters. Everything is indented by a multiple of some number of spaces, often 4.

In  statements, you indent everything you want to be run if the if conditional is. For example:

>>> James = 35 >>> Alice = 30 >>> if James > Alice: ...    print "James is older than Alice." ... James is older than Alice. >>>

Because James really is older than Alice, the  conditional is  , so Python does execute the code indented under the if line. In this case we print "James is older than Alice."

>>> James = 35 >>> Alice = 30 >>> if James < Alice: ...    print "James is younger than Alice." ... >>>

Because James is not older than Alice, the  conditional is , so Python does not execute the code indented under the if line.

In for loops, you indent everything you want to be run each loop For example:

>>> names = ["Jessica", "Adam", "Liz"] >>> for name in names: ...    print "Hello", name ... Hello Jessica Hello Adam Hello Liz

The  line is indented 4 spaces under the. That's how Python knows to execute the print line for every name in names.

Functions
Let's review what we know about functions:


 * They do some useful bit of work.
 * They let us re-use code without having to type it out each time.
 * They take input and possibly produce output (we say they return a value). You can assign a variable to this output.
 * You define a function using the def keyword.
 * You call a function by using its name followed by its arguments in parenthesis.

Here's an example:

>>> def add(x, y): ...    return x + y ... >>> add(1, 2) 3 >>> add(-1, 1) 0 >>> add(.5, .75) 1.25

Pass
pass is a keyword that just means "do nothing". It most often shows up as a place-holder for code that doesn't exist yet. For example:

>>> def testFunction: ...    pass ... >>>

Imports
Imports look like this:

>>> import random >>> import time

In the above example,  and   are both Python modules. Modules are Python files outside of the current Python file that contain Python code, like functions and variables. You can use code from modules by first importing the module. Here's an example from the module:

>>> import random >>> random.randint(0, 10) 7 >>> random.randint(0, 10) 6 >>> random.randint(0, 10) 1 >>> random.randint(0, 10) 3 >>> random.randint(0, 10) 4 >>> random.randint(0, 10) 9

is a function in the  module. It takes a lower bound as the first argument and an upper bound as the second argument and returns a random integer between those bounds.

keyword
to say backwards:

>>> fruits[::-1] ['cherries', 'bananas', 'apples']

Regular expressions

 * ^ is an anchor that means "beginning"
 * $ is an anchor that means "end"
 * . means a single wildcard character
 * .* means any number (including zero) of wildcard characters

Examples:


 * will match anything that contains "rstu", for example "understudy".
 * will match anything that starts with "aa", for example "aardvark".
 * will match anything containing "a", then any single character, then "b", then any single character, then "c", for example "iambic".
 * will match anything containing "ss", then anything, then "ss", for example "messiness".
 * will match anything that starts with "c", then any single character, then d, then any single character, then ends with an "e", for example "cadre".