# Step 14: The not Keyword¶

## Tutorial¶

In Python, we can indicate that something is not true by writing not True which is the same as False. Likewise, not False is equivalent to True.

When you solved Step 10, you created a program to have Reeborg jump hurdles.

As part of your solution for the above world, you may have created a function similar to the following:

def run_jump_or_finish():
if at_goal():
# something
elif front_is_clear():
# something
else:
# something


This program fragment can be rewritten, by choosing different combinations of the negation keyword not and different combinations of if/elif/else.

Consider the three code samples below, paying close attention to where the not keyword occur and to what is actually included in each code block.

# first choice:

def run_jump_or_finish():
if at_goal():
# something
elif not front_is_clear():
# something
else:
# something

# second choice ... trickier

def run_jump_or_finish():
if not at_goal():
if front_is_clear():
# something
else:
# something
else:
# something

# third choice:

def run_jump_or_finish():
if not at_goal():
if not front_is_clear():
# something
else:
# something
else:
# something


You have just seen how it is possible to change the order in which the conditions appear in an if/elif/else code block while still accomplishing the same goal. Two different programmers will often use different strategies to get the same final result. There are other ways in which different programmers will write different but equivalent programs: by using different functions.

The function front_is_clear() will tell Reeborg whether or not a wall is blocking its way. It will do the same for water, brick walls, fences, etc., which we have not seen yet but likely will in future worlds. There is a function that is more specific to wall called wall_in_front(); I leave it up to you to guess what it does.

Reeborg loves going for walks, especially when it is around a lake. The lakes in Reeborg’s neighborhood are all different sizes of rectangles, so Reeborg does not know how many steps it will take to get back to the start of walk. Thankfully, Reeborg happens to be carrying a banana, which you can tell Reeborg to put() down at the start of it’s walk. Reeborg knows it’s done walking when it reaches the banana again.
Use a while statement (looking for the banana object) and an if/else to have Reeborg complete his walking adventure.
Reeborg cannot use a repeat statement, since it has no idea of the dimensions of the lake it is walking around.