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Dynamic array

Array is a collection of items of same data type stored at contiguous memory locations.

In Python, it's called list.

fruits = []
fruits = ['orange', 'apple', 'strawberry']

Add element​

At the end​

Use append(item). The item will be pushed back at the end of array.

fruits = ['orange', 'apple', 'strawberry']
fruits.append('lemon')


> fruits: ['orange', 'apple', 'strawberry', 'lemon']

At anywhere​

Use insert(pos, item). The item will be inserted at position pos.

fruits = ['orange', 'apple', 'strawberry']
fruits.insert(2, 'pineapple')


> fruits: ['orange', 'apple', 'pineapple', 'strawberry']

Get array size​

Use len(arr).

fruits = ['orange', 'apple', 'strawberry']
n = len(fruits)


> n: 3

Access element in array​

Use bracket notation[index].

fruits = ['orange', 'apple', 'strawberry']
my_pick = fruits[1]


> my_pick: apple

index can be negative.

fruits = ['orange', 'apple', 'tangerine']
orange_variety = fruits[-1]     # fruits[2]


> orange_variety: tangerine

Delete element​

Use pop(index)

At the end​

fruits = ['orange', 'apple', 'strawberry']
fruits.pop()


> fruits: ['orange', 'apple']

At anywhere​

fruits = ['orange', 'apple', 'strawberry']
fruits.pop(1)


> fruits: ['orange', 'strawberry']

Delete all​

fruits = ['orange', 'apple', 'strawberry']
fruits.clear()


> fruits: []

Extend array​

Use list.extend(another_list) to concat another_list to the end of list.

zeros = [0, 0, 0]
zeros.extend(2*[0])


> zeros: [0, 0, 0, 0, 0]

Reduce array​

Use slicing to get a part of the array, then assign it to itself.

nums = [0, 1, 2, 3, 4, 5]
nums = nums[0:2]


> nums: [0, 1]
tip

When do arr[start:end], you can remember it as:

"get me that arr from start to end but end"

Useful codes​

Check if an array is empty​

Check the len

arr = []
if len(arr) == 0:
  print('Nothing is here!')
else:
  print('Array is not empty!')

Iterate over a list​

Use range(len_of_arr) to create range from 0 to len_of_arr - 1 with step = 1. Then loop through it.

arr = [4 ,8 , 2, 0, 0]
for i in range(len(arr)):
  print(arr[i], end=' ')


> 4 8 2 0 0

Iterate over a list in reverse order​

Use simple loop. Note that just like slicing array, range(start, end, step) is like "get me from start to end but not take that end".

arr = [4 ,8 , 2, 0, 0]
for i in range(len(arr) - 1, -1, -1):
  print(arr[i], end=' ')


> 0 0 2 8 4

Or using reversed(array). The array will not be affected.

wordList = 'Python is great!'
for i in reversed(wordList) :
  print(i, end='')

> !taerg si nohtyP

Oh wait, isn't wordList a string? Is it an array too?

Well, it is. Let's go to next module. 🚗