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Python example 'lesson3-BasicListStructure'
lesson3-BasicListStructure
Python beginners example: lesson3-BasicListStructure
# A list is a new data type kind of like string, int, bool, and float. The big
# difference between a list and these other types is that lists contain many
# pieces of data in it. To create a list, use square brackets, and separate
# each element in the list with commas.
animals = ["cat", "dog", "fish", "three-toed sloth"]
# We can print(lists like any other data type. (Although it doesn't look pretty))
print("The animals are: ")
print(animals)
input("Press enter to continue")
# We can also print(individual elements in a list by referencing their index.)
print("The third animal is: ")
print(animals[3])
input("Press enter to continue")
# But be careful because the indicies start at 0.
print("The zeroth animal is: " + animals[0])
input("Press enter to continue")
# If you enter too high of an index, you will get a pretty helpful error.
# Uncomment the following line to see the problem.
#print("The tenth animal is: " + animals[10])
# You can also access elements from the end of the list with negative numbers.
print("The last animal is: " + animals[-1])
input("Press enter to continue")
# Like strings, lists have a length and work with the len() function.
print("There are {} animals.".format(len(animals)))
input("Press enter to continue")
# The append method allows us to add new items to a list.
newAnimal = input("Tell me a new animal: ")
animals.append(newAnimal)
# And we can show that the list is longer now.
print("Now the animals are: {}".format(animals))
input("Press enter to continue")
# We can also remove items from a list with the remove method. Let's ditch cat.
animals.remove("cat")
print("I've removed the cat.")
print("Now the animals are: {}".format(animals))
input("Press enter to continue")
# Finally, there is a nice method to sort a list. Strings get sorted
# alphebetically, ints and float from low to high. If you have a list that
# contains both strings and numbers, this simple sort will usually not help.
animals.sort()
# And we'll print(the list one more time to see that it is sorted.)
print("The sorted animals are:")
print(animals)
# ---------------- Exercises -----------------
# 1. On line 46. Add "dinosaur" to the list of animals, then on line 47
# print(the entire list of animals.)
# 2. Modify line 46 so that it inserts dinosaur in the middle of the list
# instead of at the end. You will need to use the insert method like this:
# nameOfList.insert(indexToInsertBefore, "Thing to insert")
# 3. We saw how to remove "cat" from the list on line 51. But what happens when
# "cat" appears in the list twice. Run the program again and when it asks you
# to give a new animal, tell it "cat". Now what happens when we remove "cat"?
# Can you think of any problems that might occur?
# 4. Modify the program so that it will remove all instances of "cat" instead of
# just the first instance. You will probably need a loop.
Useful links
- Learn Python: https://pythonbasics.org
- Download Python: https://python.org