Wordplay handout

Wordplay goals

 * practice for loops
 * practice using lists
 * practice manipulating strings
 * get experience with regular expressions
 * have fun cheating at crosswords and Words with Friends

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.

range
>>> range(5) [0, 1, 2, 3, 4] >>> for i in range(5): ...    print "Hi" * i ...

Hi HiHi HiHiHi HiHiHiHi

statements inside loops
>>> for name in ["Alice", "Bob", "Cassie", "Deb", "Ellen"]: ...    if name[0] in "AEIOU": ...        print name + " starts with a vowel." ... Alice starts with a vowel. Ellen starts with a vowel.

loops inside loops
>>> letters = ["a", "b", "c"] >>> numbers = [1, 2, 3] >>> for letter in letters: ...    for number in numbers: ...        print letter * number ... a aa aaa b bb bbb c cc ccc >>> for number in numbers: ...    for letter in letters: ...        print number * letter ... a b c aa bb cc aaa bbb ccc

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
is a keyword checking for containment. You can use it in a couple of ways:

>>> "a" in "apple" True >>> "z" in "apple" False

>>> dogs = ["pug", "boxer", "dalmation"] >>> "tiger" in dogs False >>> "pug" in dogs True

Reversing lists
Here's a quick way to reverse a list.

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

Let's break down why this works:

First, remember that we can get individual elements from lists:

>>> fruits[0] 'apples'

We can also slice lists:

>>> fruits[0:2] ['apples', 'bananas'] >>> fruits[:2] ['apples', 'bananas'] >>> fruits[1:] ['bananas', 'cherries']

We can also make a copy of the list by taking a slice from the beginning to the end of the list:

>>> my_fruits = fruits[:] ['apples', 'bananas', 'cherries']

There's an extended slicing syntax that let's you say what direction you want to slice in. By default it is forward, but you can supply a 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".

To use regular expressions in Python you need to import the  library. will search for the regular expression  in the string. Here's an example to get you started:

import re s = 'Python is great!' if re.search('^.ython', s): print(s)