Reeborg is upset. It’s not raining; it’s not snowing. Yet, he cannot go outside and practise for his hurdles race.
Why, do you ask? It’s because Reeborg is waiting for you to learn about Python’s not.
Python, we can indicate that something is not true by writing not True which is synonymous of False. Likewise, not False is equivalent to True.
You have already written a program that enables Reeborg to jump hurdles; parts of it went something like this:
def run_jump_or_finish ():
if at_goal():
# something
elif front_is_clear():
# something
else:
# something
Try it!
Make Reeborg happy by re-writing this program in three other versions, by choosing different combinations of the negation keyword not and different combinations of if/elif/else.
You should use the three code samples below but pay 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; it is called wall_in_front(); I leave it up to you to guess what it does.
Try it!
Write a program using wall_in_front() instead of the equivalent not front_is_clear().