# Choose Your Own Pyventure/Wandering Grue

Functions Case Study: Wandering Grue

Let's say you'd like to have a wandering Grue in your Mysterious House that pops up in a room (or rooms) randomly.

One way to do this is to make a function that decides whether the Grue is in the room or not:

Test Frameowrk

Later in our complete code, we will see code similar to:

```eaten=grue()
if eaten:
print "Sadly, you were torn limb-from-limb by the Grue and suffered a slow, painful death."
else:
print "Congratulations, you have not been eaten by the Grue! May you have a long happy life."
```

Here we introduce a new python data type: `boolean`. Python booleans can take two values `True` and `False`. These code fragments are equivalent:

```   if x > 3:
print "yep!"

if x > 3 is True:
print "yep!"

if bool(x>3) is True:
print "yep!"
```

The "if" syntax implies if predicate is True. In Python, most things evaluate to `True`, except: None, False, 0 (0.0, etc.), empty strings, zero-length lists, dicts, and few other oddities .

Variation 1: not very random

```def grue_always():
''' this grue always appears.  returns true'''
return True
```

Our not very random grue always appears.

Exercise: Make the reverse -- a grue that never appears. The signature of the function should be `grue_never() -> False`

Variation 2: the 50/50 Grue

```import random
## random is a Python module, as mentioned above.
## We need to import it to access the random() function.
## now to begin the function definition
## Everything inside the function definition is indented! Remember, white space matters!
def random_grue():
''' boolean.  a grue that appears 50% of the time '''
## we want something that will return True 50% of the time.
## one method:  get a random float between (0,1), and return True if it's over .5
## now we need a random number. random() will give us one between 0 and 1
n=random.random() ## the random before the dot tells Python what module to look in for the function, which is the one we imported above
if n > 0.5:
grue=1 ## 1 == True
else:
grue=0 ## 0 == False

return grue ## returning allows us to capture the value
```

So what does the random_grue() function do? Let's try it. In the Python interpreter:

```    >>> import random
>>> def random_grue():
n=random.random()
if n>0/5:
grue = 1
else:
grue = 0
return grue

>>> random_grue()
1
```

The first command is to import the random module, the second is to define the function and the third is to actually call the function. The 1 is the return of the function. You may get a 1 or a 0 depending on the number random() generated. (Hint: try running it several times)

Variation 2: the Moody Grue

```import random
def grue_moody(cutoff=.5):
''' boolean.  a grue that appears (100*cutoff)% of the time '''
n=random.random()
above_cutoff = n < cutoff
return above_cutoff

def grue_moody2(cutoff=.5):
''' boolean.  a grue that appears (100*cutoff)% of the time '''
return random.random() < cutoff
```

Note that we simplified down the function quite a bit by returning the boolean value directly (especially in 'grue_moody2'), rather than doing any conditional logic to get a 1 or 0. Also notices that we specified a default value for the argument `cutoff`.

Exercises

1. Predict the behaviour of these functions calls. Then try them.
• grue_moody()
• grue_moody(-1)
• grue_moody(1)
• grue_moody("a")
• grue_moody([1,2,3])
2. Fix the code so that it prints an angry message and returns `None` if n is outside the interval (0,1).
3. try `help(grue_moody)`. What do you see?
4. what are the types of `random`, `random.random`, `random.random()`

Variation 3: the location, location, location Grue

In our final variation, we want a grue that:

• has different percentages of appearing based on which page
• should have zero chance of appearing in the main room "foyer"
• should have a default chance of appearing of 5% in rooms that aren't otherwise described
```import random
grue_fractions = { 'foyer':0, 'thedark': 1.0, 'nocake': .2 }

def location_grue(room=None, base=.05, cutoffs=dict()):
''' (boolean), does a grue appear in the room?
room : str room name
1. as written, `location_grue` has some bugs, and doesn't meet spec. Identify and fix them.
3. research the 'get' method of dictionarys... `help({}.get)`. Use this method to fix the code.