VPython Lists

By Natalie Standish

This page is to help students that are inexperienced with coding learn about the basic concepts of lists.

Types of Lists

Lists of Numbers

The most basic list is one that has numbers in it. The list of numbers may contain integers, floats, or both.

Example: numList = [1,2,3.4,5]

Lists of Strings

Lists can also be comprised of words (strings). These words must have "" surrounding them for the word to be considered a string and for the computer to accept it.

Example: strList = ["lists","are","super","cool"]

Lists of Both

Lists don't have to be made up of the same type of variable.

For example, the list ["twenty",20,5,"five"] is a valid list.

Lists of Lists

Lists can also contain lists within themselves. These are called nested loops.

Example: nested = [1,"nest",[1,2]]

Empty Lists

Empty nests are commonly used to initiate a variable and avoid program errors when calling upon that empty list. They generally have variables appended into them and grow throughout the program.

Example: []

Properties of Lists

Indices

Indexing a list is how we can identify the value at a certain spot in the list. The first component of the list is the 0th index and then it goes up by one until the last component (the nth-1 index in an list of length n). When trying to find the nth index, we use this notation: listName[n]

For example, consider the list nums = [47,36,11,19]

nums[0] = 47

nums[1] = 36

nums[2] = 11

nums[3] = 19

Appending to a List

The append function takes a previously defined/calculated value and adds it to a pre-existing list. This generally occurs in a loop and is very useful when you are trying to find patterns in the behavior of a non-static variables.

Example Code:

emptyList = []
t = 0
while t < 10:
  t = t + 1
  emptyList.append(t)

The results would give emptyList = [1,2,3,4,5,6,7,8,9,10]

Relation to PHYS 2212

Imagine you are trying to detect a pattern in the speed of a moving electron in a 30 second span of time. The code you write calculates on a loop a numerical value of the speed of the electron every second. You previously defined an empty list (elecSpeed = []). The append function takes the result calculated (Let's call this x) by the program and adds it to the list that is being appended. By putting this line of code inside of the loop, your program can create a list containing 30 calculated speeds of the electron from time t = 0 to t = 29.

Example code:

elecSpeed = []
while t < 30:
    CODE THAT CALCULATES SPEED, x
    elecSpeed.append(x)

RESULTS: elecSpeed = [x(at time t=0),x(at time t=1),x(at time t=2),..........x(at time t=29)]

References

http://openbookproject.net/thinkcs/python/english3e/lists.html