Game Development Reference
In-Depth Information
13 - Sonar Treasure Hunt
The
for
loop
for cx, cy in chests:
combines both of these principles.
Because
chests
is a list where each item in the list is itself a list of two integers, the first
of these integers is assigned to
cx
and the second integer is assigned to
cy
. So if
chests
has the value
[[5, 0], [0, 2], [4, 2]]
, on the first iteration through the loop,
cx
will have the value
5
and
cy
will have the value
0
.
Line 73 determines which is larger: the absolute value of the difference of the X
coordinates, or the absolute value of the difference of the Y coordinates. (
abs(cx - x)
< abs(cy - y)
seems like much easier way to say that, doesn't it?). The if-else
statement assigns the larger of the values to the
distance
variable.
So on each iteration of the
for
loop, the
distance
variable holds the distance of a
treasure chest's distance from the sonar device. But we want the shortest (that is, smallest)
distance of all the treasure chests. This is where the
smallestDistance
variable comes
in. Whenever the
distance
variable is smaller than
smallestDistance
, then the
value in
distance
becomes the new value of
smallestDistance
.
We give
smallestDistance
the impossibly high value of
100
at the beginning of
the loop so that at least one of the treasure chests we find will be put into
smallestDistance
. By the time the
for
loop has finished, we know that
smallestDistance
holds the shortest distance between the sonar device and all of the
treasure chests in the game.
81. if smallestDistance == 0:
82. # xy is directly on a treasure chest!
83. chests.remove([x, y])
84. return 'You have found a sunken treasure chest!'
The only time that
smallestDistance
is equal to 0 is when the sonar device's XY
coordinates are the same as a treasure chest's XY coordinates. This means the player has
correctly guessed the location of a treasure chest. We should remove this chest's two-
integer list from the
chests
data structure with the
remove()
list method.
The
remove()
List Method
The
remove()
list method will remove the first occurrence of the value passed as a
parameter from the list. For example, try typing the following into the interactive shell:
>>> x = [42, 5, 10, 42, 15, 42]
>>> x.remove(10)
>>> x
[42, 5, 42, 15, 42]
