Wordplay handout

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Wordplay goals[edit]

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

Concept review[edit]

Indentation reminder[edit]

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

In if statements, you indent everything you want to be run if the if conditional is True. 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 if conditional is True, 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 if conditional is False, 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 print line is indented 4 spaces under the for. That's how Python knows to execute the print line for every name in names.

range[edit]

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

Hi
HiHi
HiHiHi
HiHiHiHi

if statements inside for loops[edit]

>>> 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.

for loops inside for loops[edit]

>>> 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[edit]

Imports look like this:

>>> import random
>>> import time

In the above example, random and time 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 random 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

randint is a function in the random 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.

New Wordplay material summary[edit]

in keyword[edit]

in 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[edit]

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 <code>-1 to say backwards:

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

Regular expressions[edit]

  • ^ 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:

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