LIST NOTES - from W3Schools.com/python thislist = [“apple”, “banana”, “cherry”, “orange”, “kiwi”, “melon”, “mango”]

1. Accessing list items

print(thislist[1]) # print the second item of the list print(thislist[-1]) # print the last item of the list print(thislist[2:5]) # return the third, fourth, and fifth item print(thislist[:4]) # returns the items from the beginning to, but NOT including, “kiwi” print(thislist[2:]) # returns the items from “cherry” to the end print(thislist[-4:-1]) # returns the items from “orange” (-4) to, but NOT including “mango” (-1)

check if “apple” is present in the list

if “apple” in thislist: print(“Yes, ‘apple’ is in the fruits list”)

2. Changing list items

thislist[1] = “blackcurrant” # Change Item Value thislist[1:3] = [“blackcurrant”, “watermelon”] # Change a Range of Item Values thislist[1:3] = [“watermelon”] # change the second and third value by replacing it with one value thislist.insert(2, “watermelon”) # insert “watermelon” as the third item

3. Adding list items

thislist.append(“orange”) # append() method appends/adds an item thislist.insert(1, “orange”) # insert() method inserts an item at the specified index/here insertes “orange” in second posiion tropical = [“mango”, “pineapple”, “papaya”] thislist.extend(tropical) # add the elements of tropical to thislist thistuple = (“kiwi”, “orange”) thislist.extend(thistuple) # add elements of a tuple to a list

4. Removing list items

thislist.remove(“banana”) # remove the first occurrence of “banana” if it is occured many times thislist.pop(1) # Remove Specified Index/remove the second item thislist.pop() # If not specified the index, pop() removes the laste item del thislist[0] # del keyword also removes the specified index/here the first item del thislist # delete the entire list thislist.clear() # clear the list content

5. Loop lists

print all items in the list, one by one

for x in thislist: print(x)

print all items by referring to their index number

for i in range(len(thislist)): print(thislist[i])

print all items, using a `while` loop to go through all the index numbers

i = 0 while i < len(thislist): print(thislist[i]) i = i + 1

looping Using List Comprehension

a short hand `for` loop that will print all items in a list

[print(x) for x in thislist]

6. List comprehension

Without list comprehension

newlist = [] for x in thislist: if “a” in x: newlist.append(x)

With list comprehension you can do all that with only one line of code:

newlist = [x for x in thislist if “a” in x]

Syntax: newlist = [expression for item in iterable if condition == True]

newlist = [x for x in thislist if x != “apple”] # Only accept items that are not “apple”: newlist = [x for x in thislist] # with no if statement newlist = [x for x in range(10)] # you can use the range() function to create an ITERABLE newlist = [x for x in range(10) if x < 5] # Same example, but with a condition || # accept only numbers lower than 5

Expression

newlist = [x.upper() for x in thislist] # set the values in the new list to upper case newlist = [‘hello’ for x in thislist] # set all values in the new list to ‘hello’ newlist = [x if x != “banana” else “orange” for x in thislist] # return “orange” instead of “banana”

7. Sorting

thislist.sort() # sort the list alphabetically/in ascending order thislist.sort(reverse = True) # sort the list in descending order thislist.sort(key = str.lower) # Performs a case-insensitive sort of the list thislist.reverse() # Reverse the order of the list items:

sort the list based on how close the number is to 50

def myfunc(n): return abs(n - 50)

thislist = [100, 50, 65, 82, 23] thislist.sort(key = myfunc) print(thislist)

8. Copying Lists

You cannot copy a list simply by typing list2 = list1, because: list2 will only

be a reference to list1, and changes made in list1 will automatically also be made in list2. mylist = thislist.copy() mylist = list(thislist) # Another way to make a copy is to use the built-in method list(). mylist = thislist[:] # You can also make a copy of a list by using the : (slice) operator.

9. Joining Lists

list3 = list1 + list2 # Joins two lists

Appending list2 into list1:

for x in list2: list1.append(x)

Or you can use the extend() method, where the purpose is to add elements from one

list to another list:

Use the extend() method to add list2 at the end of list1:

list1.extend(list2) “”” Method Description append() Adds an element at the end of the list clear() Removes all the elements from the list copy() Returns a copy of the list count() Returns the number of elements with the specified value extend() Add the elements of a list (or any iterable), to the end of the current list index() Returns the index of the first element with the specified value insert() Adds an element at the specified position pop() Removes the element at the specified position remove() Removes the item with the specified value reverse() Reverses the order of the list sort() Sorts the list “””