Python provides support for several types of collections. A collection holds a group of items. An item may be a number, string, object or another collection.<\/p>\n
One Python collection type is a list. Each item in the list may be a different data type.<\/p>\n
Lists<\/strong><\/p>\n Lists are used to store comma separated values enclosed in brackets, example:<\/p>\n \nLists retain their order and elements in a list may be changed. \nLists may also be indexed with negative values starting at the last element. Reverse indexing starts at – 1 and decreases by -1. For example, this would also print the third element value in the list, which is ‘wash car’:<\/p>\n \nLists may be looped through by using the in keyword:<\/p>\n \n print(item)<\/p>\n Python provides support for many built in list functions. These functions are as follows:<\/p>\n append<\/strong> – Adds an element to the end of a list. Example: <\/p>\n \nclear <\/strong> – Removes all elements from the list. Example: <\/p>\n \ncopy <\/strong> – Returns a copy of the list. Example: <\/p>\n \ncount <\/strong> – Returns the number of elements in the list with the given input value. Example: <\/p>\n \nextend <\/strong> – Adds to the end of a list, another list, set, tuple, etc. Example: <\/p>\n \nindex <\/strong> – Returns the index of the input value. Example: <\/p>\n \ninsert <\/strong> – Adds an element to the list in the given index position. Example: <\/p>\n which becomes: pop <\/strong> – Removes an item from the list with the input index. Example: <\/p>\n \nremove<\/strong> – Removes an item from the list with the input value. Example: <\/p>\n \nreverse<\/strong> – Returns the list in reverse. Example: <\/p>\n \nsort<\/strong> – Sorts a list alphabetically. Example: <\/p>\n \nSorts a list descending. Example: <\/p>\n \nA custom sort function may also be defined. Example:<\/p>\n \ndef custom(element): to_do_list.sort(key=custom)<\/p>\n Returns: [‘groceries’, ‘laundry’, ‘shovel snow’, ‘vacuum’, ‘wash car’]<\/p>\n A couple of other useful Python methods for lists are:<\/p>\n del<\/strong> – Delete an element from a list. This does not return a value. Example: <\/p>\n \n This deletes the entire list: <\/p>\n \nlen<\/strong> – Returns the number of elements in a list. Example: <\/p>\n \nlist<\/strong> – Constructor used to create a list. Example: <\/p>\n \nmin<\/strong> – Returns the item with the minimum value. Example: <\/p>\n \nmax<\/strong> – Returns the item with the maximum value. Example: <\/p>\n Slicing<\/strong><\/p>\n Ranges of list items can be accessed by slicing. This is done by indexing the list with a beginning index followed by a colon and an ending index. The beginning index is inclusive. The ending index is exclusive. Example:<\/p>\n Extract elements 2 – 3 which would be indexes 1 – 2.<\/p>\n Using the original list, this returns: to_do_list[‘laundry’, ‘wash car’] which is: If the beginning index is not included, the slicing starts at the first element in the list.<\/p>\n If the ending index is not included, the slicing ends at the last element in the list.<\/p>\n If neither the beginning index or ending index is included, the slicing starts at the first element and ends at the last element.<\/p>\nto_do_list = ['groceries', 'laundry', 'wash car', 'vacuum']<\/pre>\n
\nList elements have a corresponding index value. Indexing starts at 0 and increases by 1. Elements are accessed by using their index value.
\nFor example this would print the third element value in the list, which is ‘wash car’:<\/p>\nprint(to_do_list[2])<\/pre>\n
print(to_do_list[-2])<\/pre>\n
for item in to_do_list:<\/pre>\n
to_do_list.append('exercise')<\/pre>\nto_do_list.clear()<\/pre>\n
new_list = to_do_list.copy()<\/pre>\n
to_do_list.count('vacuum')<\/pre>\nto_do_list.extend(['wash dishes', 'take nap'])<\/pre>\n
to_do_list.index('vacuum')<\/pre>\nto_do_list.insert(1, 'shovel snow')<\/pre>\n
\nto_do_list = [‘groceries’, ‘shovel snow’, ‘laundry’, ‘wash car’, ‘vacuum’]<\/p>\nto_do_list.pop(2)<\/pre>\n
to_do_list.remove('vacuum')<\/pre>\nto_do_list.reverse()<\/pre>\n
to_do_list.sort()<\/pre>\n
to_do_list.sort(false)<\/pre>\n
<\/pre>\n
\n return element[0]<\/p>\ndel to_do_list[2]<\/pre>\n
del to_do_list<\/pre>\n
num = len(to_do_list)<\/pre>\n
new_list = list(('exercise', 'shovel snow'))<\/pre>\nto_do_tuple.min() # returns 'groceries'<\/pre>\n
to_do_tuple.max() # returns 'wash car'<\/pre>\n
extracted_list = to_do_list[1:3]<\/pre>\n
\n[element 2, element 3] which is:
\n[index 1, index 2]<\/p>\nextracted_list = to_do_list[:3] # returns to_do_list['groceries', 'laundry', 'wash car']<\/pre>\n
extracted_list = to_do_list[1:] # returns to_do_list['laundry', 'wash car', 'vacuum']<\/pre>\n
extracted_list = to_do_list[:] # returns to_do_list['groceries', 'laundry', 'wash car', 'vacuum']<\/pre>\n