LIST METHODS

list creation

• created by placing all the items (elements) inside a square bracket [], separated by commas

• can have any number of items and they may be of different types (int, float, string, etc)

• Sample: name = [1,2,3] # same data types

• Sample: name = [‘1’, 2, 3.4] # mixed-data types

slice list

• accessing range of items in a list by using the slicing operator [] using colon :

• can be best visualized by considering the index to be between the elements

• last number is not included in the display

• Syntax: start:end

• Sample: [0:4] #positive →

• Sample: [-2:-1] #negative → starts at the end element

append()

• a list method that adds an element (single item) to the end of the list

• it only modifies the original list, doesn’t return any value

• takes a single item and adds it to the end of the list

• item can be number, string, another list, dictionary, etc

• Syntax:list.append(item)

count()

• its a method that counts how many times an element has occured in a list and returns it

• it takes a single element

  • element - element whose count is to be found

• this method returns the number of occurences of an element in a list

• Syntax: list.count(element)

extend()

• this method extends the list by adding all items of a list to the end

• it takes a single argument (a list) and adds it to the end

• this method also add element of other native data types, like tuples and set to the list

• Syntax: list.extend(tuple_type)

index()

• this method search and find given elements in the list and return its position

• if the same element is present more than once, this method returns its smalles/first position

• indexces in python starts at 0

• this method returns the index of the element in the list

• this method takes a single argument

  • element - element that is to be searched

• Syntax: list.index(element)

insert()

• this method inserts the element to the list at the given index

• it function takes two parameters:

  • index - position where element needs to be inserted

  • element - the element ton be inserted in the list

• this method only inserts the element to the list, it doesnt return any value

• Syntax: list.insert(index, element)

pop()

• this method takes a single argument (index) and removes the element present at that index from the list

• if the index passed to this is not in the range, it throws an error (out of range exception)

• the parameter passed to this method is optional

  • if no parameter is passed, the default index -1 is passed as an argument

• this method removes and returns the element at the given index and updates the lsit

• Syntax: list.pop(index)

copy()

• this method (also known as aliasing) returns a shallow copy of the list

• a list can be copied with = operator

  • old_list = [1,2,3]

  • new_list = old_list

• the problem with this is the list in this way is that if you modify the new_list, the old_list will also be modified

• Syntax: new_list = old_list

shallow copy

• using this method, you can keep the original list (unchanged) when the new list is modified

• the copy() doesn’t take any parameters

• it will return a list, doesnt’t modify the original list

• Syntax: new_list = list.copy()

remove()

• this method searches for the given element in the list and removes the first matching element

• it takes a single element as an argument and removes it from the list

• if the element passed to this method doesn’t exist, valueError exception is thrown

• Syntax: list.remove(element)

reverse()

• this method reverses the elements of a given list

• the function doesn’t return any value

  • only reverses the elements and updates the list

• Syntax: list.reverse()

sort()

• this method sorts the elements of a given list in a specific order → ascending or descending

• Syntax: list.sort()

dictionary

• this is an unordered collection of items; has a key: value pair

• in creating this, you place items in a curly braces {} separated by comma

• an item has a key and the corresponding value expressed as a pair, key:value

• while values can be of any data type and can repeat, keys must be of immutable (string, number, or tuple) with immutable elements) and must be unique