21/01 - Lists

#list - ordered sequence of objects of any type. Some examples:

# li = [1,2,3,4,5]
# li2 = ['a','b','c']
# lie3 = [1,2,'a', True]

#lists are effectively a form of Array in python

# lists are a data structure
#Data Structure - way to org info/data into a folder, to use with diff pros and cons
#the [] allows data to be contained

# amazon_cart = ['notebooks', 'sunglasses']

# print(amazon_cart[0]) # as with strings/indexes, in a list each item is assigned a number, here 0 is 'notebooks'

#list slicing - similar to string slicing where you'd have [0:2:1] for start/end/skip

# amazon_cart = [
#     'notebooks',
#     'sunglasses',
#     'toys',
#     'grapes']

# amazon_cart[0] = 'laptop'#this will now change item 0, notebooks, into laptop
    
# #print(amazon_cart[0::2])# as with strings, this will start at 0, end at the end and skip every 2nd item

# #lists are mutable/changeable

# # print(amazon_cart[1:3])

# new_cart = amazon_cart[0:3]
# new_cart[0] = 'gum'
# print(new_cart)
# print(amazon_cart) # here the original list is still printed, as list slicing creates a new copy

#without list slicing e.g. [:], the original will be replaced instead of making a copy

#e.g. new_cart = amazon_cart[:] will retain both carts when asked to print both

#matrix - a way to describe multi-dimensional lists

# matrixgoop = [
# [1,2,3],
# [2,4,6],
# [7,8,9]
# ]

# #the above provides a main array with 3 sub-arrays inside

# print(matrixgoop[0][1]) # in a situation like this, the matrix will access the first section of the array [1,2,3], and then take the item in slot 1 from the first sub array, which is 2

#List Methods

#basket = [1,2,3,4,5]

#adding
#new_list = basket.append(100) #changes the list in place, rather than creating a new one
#basket.append(100)# in doing this individually, both lists will be = basket
#basket.insert(4, 100) # adds 100 to the index 4
#basket.extend([100,101])# extends the list with new numbers provided

#removing

#new_list = basket
#basket.pop() #removes whatever is at the end of the list, here it removes 5
#basket.pop(0) # removes the item at index 0, here it is 1
#basket.remove(4) # does what it says on the tin, give it a specific value to remove, rather than an index
#print(basket)
#new_list = basket.pop(4)#this will return the item that has been popped, here it will be index 4, number 5
#new_list = basket.clear()#as expected, this clears the whole basket
#print(basket)

#index

#print(basket.index(2))#will give us index of the value, so here 2 is at index 1, will print 1
#print(basket.index(2,0,2))#this will give a start and stop point of 0,2 in the index

#print(2 in basket)# the in function asks if value is in the list, giving true or false
#print('i' in 'hi my name is ian')# checks if value is in the string
#print(basket.count(2))# this will count how often the given value appears in the list

#basket.sort()#will sort the basket in place

#print(sorted(basket))# sorted produces a new list/array
#print(basket)# the original basket will remain the same

#basket.copy does the same as basket[:]

#basket.reverse()#prints the basket in reverse order who'd have guessed, no sorting occurs
#print(basket)

#Common List Patterns

# basket=['a','x','b','c','d','e','d']
# basket.sort()
# basket.reverse()
# print(basket[::-1])#this reverses the basket again, returning it to regular order. Slicing also creates a new list
# print(basket)

#print(list(range(100)))#range allows a list to be created with a range of values, e.g. here it will give 0-99

#sentence = ' '
#new_sentence = sentence.join(['hi','my','name','is','jojo'])# joins the contents with the str of sentence, such as a space
#new_sentence = ' '.join(['hi','my','name','is','jojo'])# same situation without need for another variable
#print(sentence)
#print(new_sentence)

#List Unpacking

# a,b,c, *other, d = [1,2,3,4,5,6,7,8,9]

# print(a)
# print(b)
# print(c)
# print(other)
# print(d)

#None - special data type to represent absence of value, similar to Null in other lang

#weapons = None
#print(weapons)