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lab4

Lab 4: List Functions

In this lab, we are going to furthur explore the data structure List and practice writing functions with List. Start by forking this lab into your repository or cloning it to your local machine as we covered in Lab 3. You can find clone instruction here.

Review on List

Create a list:

empty_list = []
fruits = ['apple', 'banana', 'cherry']

Access items:

Python console
>>> my_fruit = fruits[1]
>>> print(fruits[1])
'banana'

Change item value:

Python console
>>> fruits[0] = 'strawberry'
>>> print(fruits)
['strawberry', 'banana', 'cherry']

Loop through a list:

for x in fruits:
    print(x)

List length:

Python console
>>> print(len(fruits))
>>> 3

Add item:

Python console
>>> fruits.append('dragon fruit')
>>> print(fruits)
['strawberry', 'banana', 'cherry', 'dragon fruit']
>>> fruits.insert(1, 'mango')
>>> print(fruits)
['strawberry', 'mango', 'banana', 'cherry', 'dragon fruit']

Remove item:

Python console
>>> fruits.remove('strawberry')
>>> print(fruits)
['mango', 'banana', 'cherry', 'dragon fruit']
>>> fruits.pop()
>>> print(fruits)
['mango', 'banana', 'cherry']

Filter:

Python console
>>> num_list = [-2, -1, -4, 1, 2]
>>> positive_list = list(filter(lambda x: x > 0, num_list))
>>> print(num_list)
[1, 2]

Write functions

Open lab4 and implement the functions. Here are some key concepts we want to explain:

Make a copy vs Modify in place:

Make a copy requires you to return a new object, which is a different object from the given list, but with the same value. Modify in place requires you to modify the given list, without creating any new object.

Selection Sort:

The selection sort algorithm sorts an array by repeatedly finding the minimum element (considering ascending order) from unsorted part and putting it at the beginning. The algorithm maintains two subarrays in a given array.

  1. The subarray which is already sorted.
  2. Remaining subarray which is unsorted.
arr = 64 25 12 22 11

// Find the minimum element in arr[0...4] and place it at beginning
11 25 12 22 64

// Find the minimum element in arr[1...4] and place it at beginning of arr[1...4]
11 12 25 22 64

// Find the minimum element in arr[2...4] and place it at beginning of arr[2...4]
11 12 22 25 64

// Find the minimum element in arr[3...4] and place it at beginning of arr[3...4]
11 12 22 25 64

Here is a video that illustrates how selection sort works.

Test your functions

To test our functions, we are going to use pytest as covered in Lab3. First check the Python interpreter on your computer to be one of the below:

  • py (Windows)
  • python3 (Mac?)
  • python3.7 (Windows?)
  • python37 (Mac)
  • C:\Python37\python.exe (definitely Windows)
  • python Now, from within the lab3 directory, run this (replacing $PY with your Python):
Mac$ $PY -m pipenv install --dev
Win> $PY -m pipenv install --dev

Once it’s ready, check that it's good to go by running pytest:

Mac$ $PY -m pipenv run pytest
Win> $PY -m pipenv run pytest

If all functions are implemented correctly, your code should pass all tests.