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Part 4, More Loops

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    Jacob Aronoff

And we're back (after a slight hiatus)! Let another day of Python begin!! So let's back up for a second. We can make variables really easily:

b=9#and so forth

And right now if we wanted to print out all the numbers between 1 and 100 we could do this:

while num <= 100:
    num = num +1

This will print all the numbers between 0 and 100 (inclusive). Okay now for the new stuff. Let's say we were in a classroom, in that class we have a bunch of students.

student1 = "Jacob"
student2 = "Sam"
student3 = "Corey"
student4 = "Michael"

#If we wanted to print each student:

As you can tell this is a bit annoying, lets say (theoretically) our classroom had 100 kids, we would have to write 100 print statements! In order to make this easier we can have a list of students.

students = ["Jacob", "Sam", "Corey", "Michael"]

So now we have a list of four students. Right now the only way we can print out each student is like this:

num = 0
while num<len(students): #len is a built in function like print that tells us how long something is, it could be an array, a string, etc.
    num = num + 1

We access what's called an index in our array with [somenumber]. But be careful with this, because if the length of our array is 4 and we ask for the object at the fifth index: students[4] (keep in mind that programmers start counting at 0) we'll get an error! The easiest way to avoid this is by using a new kind of loop!

for student in students:

The magical for loop can do some awesome stuff. We can use it to iterate through a list, a string, and even a range of numbers!

for num in range(0,10):#range is another built in function in python
    print(num)#prints 0 through 9

With python, we can have lists of strings, and numbers together. Lists have some built in functions that are really useful:

list = ["string1",10,"string2",100]
if 10 in list:
    for thing in list:

Here are some of the functions of array:

  • list.append(obj) #add an object to the end of an array
  • list.count(obj) #count the amount of times the object shows up in the array
  • list.index(obj) #where's the first occurance of the object
  • list.insert(index, obj) #put an object at a certain place
  • list.remove(obj) #get rid of an object if it's there

Next time we're going to go over a different kind of list called a dictionary. In the meantime, I'd suggest to make a program that uses lists and some of the other things we've learned.