F3 CL Python Assignment 4: Lists
Table of Contents
What is a list? #
Data types #
In Python, there are generally tow kinds of data type: Atomic and Collective.
Atomic data types, as its name suggests, atomic data types cannot be further broken down. For example a boolean True or an int 69.
List #
A list is a collective data type. It is made up of other atomic or collective data types. Here is an example:
demo = [0, 1, 2, 3, 4] # this is an example of a list
Unlike many other languages, in Python you can put different kinds of data types in one single list.
demo = ["computer", "club", "No." 1,] # a list made up of `str` and `int`
Iterable #
A list is an iterable. An iterable is any Python object capable of returning its members one at a time, permitting it to be iterated over in a for-loop.
demo = [1, 2, 3]
for number in demo:
print(number)
Output:
1
2
3
For further information, please refer to the school pdf of this lesson. Note that you can pass a number into pop() to remove an item with specific index.
Exercise #
Introduction #
We are given a list T which represents temperatures of regions. Put that to your Python file first.
T = [ 19.6, 18.7, 18.8, 20.1, 19.6, 19.6, 19.6, 18.2,
18.3, 18.5, 18.8, 18.8, 13.5, 17.9, 19.7, 19.1,
19, 19.3, 19.1, 18.7, 18.9, 19.7, 18.3, 18.6,
18.1, 12.8, 19, 13.6, 16, 18.4, 19.6, 17.6,
19.4, 19.7, 19.9, 19.2, 19.7, 18.6, 19.1]
Our job is to :
- Evaluate the total number of regions
- Count the number of regions with a temperature above 18.5 C.
- Calculate the average temperature over all regions.
First think about what can we do to solve this with our previous knowledge!
Ready?
1. Total number of regions #
The first one is too easy. We will just use a len():
total_number = len(T)
print(f"The total number of regions: {total_number}")
Note that we can put a f before the string and we can put our variable inside the curly brackets. it is equivalent to:
print("The total number of regions:", len(total_number))
2. Number of regions with temp > 18.5 #
To count the total number of temperature above 18.5, we need to check every number in the list to check whether it is larger than 18.5 or not.
Let’s first create a variable to store our counts:
count_larger = 0
To go through every item in the list, we can use a for loop. Since a list is an iterable we can put it in a for loop. Let’s call each temperature in the list temp:
for temp in T:
And finally, use a if to check if temp is larger than 18.5. If yes, we will add one to count:sum = 0
count = 0
count_larger = 0
for temp in T:
if temp > 18.5:
count_larger += 1
print(f"Number of regions with temperature above 18.5 degC: {count_larger}")
Good. Now let’s run the program and see if it returns 27:
Output:
The total number of regions: 39
Number of regions with temperature above 18.5 degC: 27
3. Average #
Now let’s move to the next task. To calculate the average of the numbers, we first have to get the sum of all the numbers. To do this, we first have to make a new variable to store the sum:
sum = 0
What we are going to do is loop through the entire list and add each number to sum.
Let’s make a new for loop… Wait!
Remember we have made a loop previously? Why not just modify that loop?
sum = 0
count_larger = 0
for temp in T:
sum += temp
if temp > 18.5:
count_larger += 1
print(f"Number of regions with temperature above 18.5 degC: {count_larger}")
print(f"sum: {sum}") # for testing only, should be deleted afterwards
Let’s run the code first.
Output:
The total number of regions: 39
Number of regions with temperature above 18.5 degC: 27
sum: 721.1000000000003
Note that the output is a bit weird. What is that 000000000003 ?
The computer club will soon publish and article about that, but now let’s ignore that since it doesn’t really matter.
Next we will divide it by the total number of regions(length of the list) and round it off to 2 dp using round().
average = round(sum / total_number, 2) # the `2` specifies 2 decimal points
print(f"Average temperature: {average}")
Now everything is done. Let’s run our program:
Output:
The total number of regions: 39
Number of regions with temperature above 18.5 degC: 27
Average temperature: 18.49
Bonus: Better ways? #
Actually, we can use Python’s built-in functions to simplify our program e.g. sum() returns the sum of a list.
If you are pro enough, you can do it with one line like Nick:
print(f"The total number of regions: {len(T)}\nNumber of regions with temperature above 18.5 degC: {len(list(filter(lambda x: x > 18.5, T)))}\nAverage temperature: {round(sum(T) / len(T), 2)}")
The filter() function takes two parameters. The first one is a function that returns a boolean(in this case we use a lambda function which receives a parameter and compare it with 18.5). The second one is an iterable. After that filter() will execute the function for each item in the iterable and pass that item to the function as the parameter, and store the item into a filter object if it returns True. Next we will use list() to convert the object into a list.