Python Lists

Lists in Python

• Lists and Tuples are used for working with sequential data.
• Sets are unordered collections of unique values.
• Lists allow working with a list of values.
• Lists are created using square brackets [].
• Values within the list are separated by commas.
• Example: courses = ['history', 'math', 'physics', 'compi']

Length and Accessing Values

• The number of values in a list can be determined using the len() function.
• Example: len(courses) would return 4 for the example list.
• Values in a list are accessed using square brackets [] with the index of the value.
• List indexes start at 0.
• To access the first value: courses[0] (would return 'history').
• The last value in a list can be accessed using an index of -1.
• Accessing an index that doesn't exist will result in an IndexError.

Slicing Lists

• You can access a range of values from a list
• Use square brackets with a starting and stopping index [start:stop]
• The starting index is inclusive
• The stopping index is exclusive.
• Example: courses[0:2] would return ['history', 'math'].
• Omitting the first index assumes starting at the beginning of the list.
• Omitting the second index assumes going to the end of the list.

List Methods for Modification

• The append() method adds an item to the end of the list.
• Example: courses.append('art') adds 'art' to the end.
• The insert() method adds an item at a specific index.
• Takes two arguments: index and value to insert.
• Example: courses.insert(0, 'art') inserts 'art' at the beginning.
• The extend() method adds multiple values from another list to the end of the current list.
• Takes a single argument, which is the iterable (e.g., another list).
• Example: courses.extend(courses2) adds all values from courses2 to courses.

Removing Items

• The remove() method removes a specific value from the list.
• Example: courses.remove('math') removes 'math' from the list.
• The pop() method removes the last value of the list by default.
• pop() can also remove a value at a specific index if provided as an argument.
• pop() returns the value that was removed.

Sorting Lists

• The reverse() method reverses the order of the list.
• The sort() method sorts the list in place (modifies the original list).
• Strings are sorted alphabetically
• Numbers are sorted in ascending order.
• To sort in descending order, pass reverse=True to the sort() method.
• The sorted() function returns a sorted version of the list without modifying the original.
• Example: sorted_courses = sorted(courses)

Built-in Functions for Sequences

• min(): Returns the minimum value in a sequence.
• max(): Returns the maximum value in a sequence.
• sum(): Returns the sum of all values in a sequence.

Finding Values

• The index() method finds the index of a specific value in the list.
• Example: courses.index('compi') returns the index of 'compi'.

Finding Index and Checking Values

• The index() method finds the index of a specified value in a list.
• If the value doesn't exist, a ValueError is raised.
• The in operator checks if a value exists in a list, returning True or False.

Looping Through Lists

• A for loop iterates through each item in a list.
• Code within the loop is indented to indicate its execution for each item.
• The enumerate() function provides both the index and value during iteration.
• enumerate() can start from a specified index by using the start argument.

Converting Lists to Strings and Back

• The join() method concatenates list elements into a string, using a specified separator.
• Useful to turn list of courses into comma separated values.
• The split() method divides a string into a list, based on a specified delimiter(separator).

Tuples: Immutable Sequences

• Tuples are similar to lists but are immutable (cannot be modified after creation).
• Lists are mutable, meaning their elements can be changed.
• Assigning one list to another creates two variables that point to the same mutable object such that changing one changes the other.
• Attempting to modify a tuple raises a TypeError.
• Tuples have fewer methods than lists due to their immutability.
• Tuples are defined using parentheses ().

Sets: Unordered Collections of Unique Elements

• Sets are unordered collections of unique elements, meaning no duplicates are allowed.
• Sets eliminate duplicate values.
• Sets are defined using curly braces {}.
• Sets are optimized for membership tests (checking if a value belongs to the set).
• Can be used test whether a value is part of the set.
• Sets use Intersection method to efficiently determine values they share
• Sets use Difference method to efficiently determine values one set has that other sets don't have
• Sets use Union method to combine all courses from both sets

Set Operations: Intersection, Difference, Union

• intersection() returns common elements between sets.
• difference() returns elements present in one set but not in another.
• union() combines all elements from both sets.

Creating Empty Lists, Tuples, and Sets

• Empty lists can be created using [] or list().
• Empty tuples can be created using () or tuple().
• Empty sets must be created using set(), not {} (which creates an empty dictionary).