What is a Sequence?

A sequence in Python is a container, storing ordered collection of objects.

What is a Sequence?

The position number of an item in a sequence is called index.

Indexes starts counting from 0.

All sequence data type in Python supports common sequence operations.

length, indexing, slicing, concatenation, repetition, membership test, min, max, count, index.

Each sequence data type has also own methods for performing specific operations.

What is a Sequence?

What is a Sequence? - examples

			# list:
			fruits = ["apple", "banana", "strawberry", "banana", "orange"]

			# tupple:
			point3d = (4, 0, 3)

			# range:
			digits = range(0,10)

			# string:
			user_name="ada byron"
		

The Sequence Data Types in Python are:

Lists.

Tuple.

Range.

Strings are also considered as a sequence.

What is a List?

A list is a mutable (i.e. changeable) sequence of objects.

we can add or delete elements to the list.

Lists, being mutable sequence, can grow or shrink.

There is no restriction of the type of the objects being in a list.

The objects in a list can repeat many times.

Lists are general-purpose data structure.

Create list by literal

A List literal is denoted by a square brackets

Items in the list are separated by comma

			### create empty list:
			empty_list = []

			### create list of numbers:
			users = [1,2,3,4,5]

			### create list of lists
			matrix = [
				[1,2,3],
				[4,5,6],
				[7,8,9]
			]
		

Retrieve item from list

			var_name = list_name[index]
		

			### create list:
			fruits = ["apple", "banana", "strawberry", "banana", "orange"]

			### retrieve the first item in the list:
			item1 = fruits[0]
			# apple

			### retrieve third item in the list.
			item3 = fruits[2]
			# strawberry

			# retrieve last item in the list:
			itemN = fruits[-1]
			# orange
		

We will discuss more indexing operation in Common Sequence Operations.

Change list item

			list_name[index] = value
		

			### create list:
			fruits = ["apple", "banana", "strawberry"]

			### Change second list item
			fruits[1] = "plum"
			print( fruits )
			# ['apple', 'plum', 'strawberry']

			### Change last list item
			fruits[-1] = "orange"
			print( fruits )
			# ['apple', 'plum', 'orange']
		

What is a Tuple?

A tuple is immutable (i.e. not changeble) sequence of data.

once created a tuple can not be changed! No grow or shrink can happens.

Useful for fixed data.

Tuples are faster than lists and consumes less memory, but they are not general-purpose.

Create tuple from literal

Tuple literal is denoted by parentheses

Items in the tuple are separated by comma

			### create empty tuple:
			empty = ()
			print( empty )
			# ()

			### create tuple with one element - note the trailing comma!
			t = (99,)
			print(t)
			# (99,)

			### create tuple of 3 elements:
			point3d = (4, 0, 3)
			print(point3d)
			# (4, 0, 3)
		

Retrieve item from tuple

			var_name = tupple_name[index]
		

			### retrieve tuple items
			address = ('Bulgaria', 'Sofia', 'Nezabravka str', 14)

			country = address[0]
			town = address[1]
			street = address[2]
			street_num = address[3]
			print(country, town, street, street_num)
			# Bulgaria Sofia Nezabravka str 14
		

Change tuple? No Way!

Tuples are immutable and can not be changed!

			### change a tuple item:
			address[0] = "France"
			# TypeError: 'tuple' object does not support item assignment
		

Examples

			### create tuple with 3 elements:
			ada_birth_date = (10, "December", 1815)

			# retrieve tuple elements:
			ada_birth_day = ada_birth_date[0]
			ada_birth_month = ada_birth_date[1]
			ada_birth_year = ada_birth_date[2]

			print("Ada is born on {} {} in {}".format(ada_birth_month, ada_birth_day, ada_birth_year))
			# Ada is born on December 10 in 181
		

Performance

Tuples requires less memory and are faster than lists

Usage

Use list, when you want to add/remove/change items in the list

Use tuple, when you want to preserve your data from being changed

What is a Range Object?

The range type represents an immutable sequence of numbers.

It's used to generate a number sequence, limited between pre-given start and stop integer values.

It's typical use in Python is with for loops.

Syntax

			range(stop)
			range(start, stop[, step])
		

start is optional and if omitted defaults to 0

step is optional and if omitted defaults to 1.

start, stop and step must be integers!

step can't be 0 (or "ValueError" is raised)

The range of generated integers will end at stop - 1.

If the given arguments did not form a sequence, an empty sequence will be returned.

Examples

			range(0,10)
			# generates the sequence: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

			range(10)
			# same as above

			range(2,10,2)
			# generates the sequence: [2, 4, 6, 8]

			range(9, -1, -1)
			# generates the sequence: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

			range(9, -1, 1)
			# incorrect sequence formulae, will return empty sequence
		

Range in for: example 1

			### iterate from 0 up to 10, step = 1 (default)
			for i in range(0,10):
			    print(i, end=" ")
			# 0 1 2 3 4 5 6 7 8 9
		

Range in for: example 2

			### iterate from 10 up to -1, step = -1
			for i in range(10,-1, -1):
			    print(i, end=" ")
			# 10 9 8 7 6 5 4 3 2 1 0
		

Range in for: example 3

			### iterate from 2 up to 10, step = 2
			for i in range(2, 10, 2):
			    print(i, end=" ")
			# 2 4 6 8
		

Range in for: example 4

			### iterate from -10 up to 0, step = 2
			for i in range(-10, 0, 2):
			    print(i, end=" ")
			# -10 - 8 - 6 - 4 - 2
		

Range in for: example 5

			### iterate from 0 (Default) up to 10, step=1 (Default)
			for i in range(10):
			    print(i, end=" ")
			# 0 1 2 3 4 5 6 7 8 9
		

Next operation can be used on all sequence types, with the exception that range() objects can not be concatenated or repeated (but the sequences they produced can).

Concatenation +

Concatenate two sequences and return the resulting sequence

				### Let's have two lists:
				fruits = ["apple", "banana", "strawberry"]
				numbers = [1,2,3]

				### We can concatenate them:
				concat_list = fruits + numbers
				print(concat_list)
				# ['apple', 'banana', 'strawberry', 1, 2, 3]
		

Concatenation - lists example

			num_list = [1,2,3]
			alpha_list = ["a", "b", "c"]

			conc_list = num_list + alpha_list
			print(conc_list)
			# [1, 2, 3, 'a', 'b', 'c']
		

Note, that the result is a list!

Concatenation - tuples example

			date1 = (31, "Decemeber", 2017)
			date2 = (10, "Mart", 1999)

			conc_date = date1 + date2
			print(conc_date)
		

Note, that the result is a tuple!

Repetition *

Repeats a sequence a given number of times and return the resulting sequence

The multiplier must be an integer value!

			### Let's have a list:
			numbers = [1, 2, 3]

			### Repetition
			rep_list = numbers * 3
			print(rep_list)
			# [1, 2, 3, 1, 2, 3, 1, 2, 3]
		

Repetition - example

			num_list = [1, 2, 3]
			alpha_list = ["a", "b", "c"]

			print(num_list*3)
			print(alpha_list*3)
			# [1, 2, 3, 1, 2, 3, 1, 2, 3]
			# ['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c']
		

Membership Testing in, not in

x in sequence

returns True if x is member of sequence

returns False if x is NOT member of sequence

x not in sequence

returns True if x is NOT member of sequence

returns False if x is member of sequence

Membership Testing - list example

			### Let's have two list:
			fruits = ["apple", "banana", "strawberry"]
			numbers = [1, 2, 3]

			### Membership Testing (in):
			print("banana" in fruits)
			# True

			print("banana" in numbers)
			# False

			### Membership Testing (not in):
			print("banana" not in fruits)
			# False

			print("banana" not in numbers)
			# True
		

Membership Testing - range example

			# Let's have a range:
			r = range(0,10)
			print(3 in r)
			# True

			print(21 in r)
			# False
		

Indexing from start to end

First sequence item is with index 0.

Next sequence item indexes increments with 1

Indexing from start to end - example

				### create list of numbers:
				numbers = [1,2,3,4,5]

				### index from start to end:
				print(numbers[0],numbers[1],numbers[2],numbers[3],numbers[4])
				# 1 2 3 4 5
			

Indexing from end to start

Last list item is with index -1

Next sequence item indexes decrements with 1

Indexing from end to start - example

			### create list of numbers:
			numbers = [1,2,3,4,5]

			### index from end to start:
			print(numbers[-1],numbers[-2],numbers[-3],numbers[-4],numbers[-5])
			# 5 4 3 2 1
		

Slicing - syntax

			sliced = sequence[start:end:step]
		

Slice a sequence from start to stop whit the given step

start, end and step are optional!

At least one column (:) is required!

			>>> str = "abcdef"

			>>> str[:]
			'abcdef'

			>>> str[2:4]
			'cd'

			>>> str[]
			SyntaxError: invalid syntax
		

Slicing - use cases

			# get items from start through end-1
			s[start:end]

			# get items from start through the rest of the array
			s[start:]

			# get items from the beginning through end-1
			s[:end]

			# get items from begining through the end
			# i.e. copy of the whole array
			s[:]
		

Slicing - examples

			>>> str = "abcdef"

			>>> str[0:3]
			'abc'

			>>> str[:3]
			'abc'

			>>> str[2:3]
			'c'

			>>> str[3:]
			'def'

			>>> str[-1:-7:-1]
			'fedcba'
		

Syntax

			for item in sequence:
			    # do something with item
		

			### loop on list items:
			for item in [1,2,3]:
			    print(item)

			### loop on tuple items:
			for item in (10, "December", 1985):
			    print(item)

			### loop on string items:
			for item in "byron":
			    print(item)

			### loop on range items:
			for item in range(1,3):
			    print(item)
		

Create list from sequence: list()

With list() function we can create a list from any sequence:

			### list from tupple:
			point3d = (4, 0, 3)
			point3d_list = list(point3d)
			print(point3d_list)
			# [4, 0, 3]

			### list from range:
			digits = range(0, 10)
			digits_list = list(digits)
			print(digits_list)
			# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

			### list from string:
			user_name = "ada byron"
			user_name_list = list(user_name)
			print(user_name_list)
			# ['a', 'd', 'a', ' ', 'b', 'y', 'r', 'o', 'n']
		

Other List Operations

			fruits = ["apple", "orange", "strawberry"]
			### Delete a list item by index
			del fruits[1]

			print(fruits)
			# ['apple', 'strawberry']
		

Basic List Methods

			### Create list of fruits:
			fruits = ["apple", "banana", "strawberry"]

			### Appends item the end of the list:
			fruits.append("plum")
			print(fruits)
			# ['apple', 'banana', 'strawberry', 'plum']

			### Insert item in specified position (by the index given as first parameter)
			fruits.insert(2, "NEW")
			print(fruits)
			# ['apple', 'banana', 'NEW', 'strawberry', 'plum']

			### Retrieve the item at the end and remove it from the list:
			item = fruits.pop()
			print(item, fruits)
			# plum ['apple', 'banana', 'NEW', 'strawberry']

			### Retrieve the item at the index given and remove it from the list:
			item = fruits.pop(2)
			print(item, fruits)
			# NEW ['apple', 'banana', 'strawberry']

			### Remove the first item from a list by the given value:
			fruits.remove("banana")
			print(fruits)
			# ['apple', 'strawberry']

			### Reverse the items of a list in place:
			fruits.reverse()
			print(fruits)
			# ['strawberry', 'banana', 'apple']
		

Lists of lists

A list item can be any data type, including list, tuples and so on.

			### create list of lists:
			matrix = [
			    [1,2,3],
			    [4,5,6],
			    [7,8,9],
			]

			### retrieve the first element from the first list:
			print(matrix[0][0] )
			# 1

			### retrieve the last element from the first list:
			print(matrix[0][-1])
			# 3

			### retrieve the first element from the last list:
			print(matrix[-1][0])
			# 7

			### retrieve the last element from the last list:
			print(matrix[-1][-1])
			# 9
		

List of tuples

			### create list_of_tuples:
			points = [
			    (1,2),
			    (3,4),
			    (5,6)
			]

			### retrieve the first element from the first tuple:
			print(points[0][0])
			# 1

			### retrieve the last element from the first tuple:
			print(points[0][-1])
			# 2

			### retrieve the first element from the last tuple:
			print(points[-1][0])
			# 5

			### retrieve the last element from the last tuple:
			print(points[-1][-1])
			# 6
		

Create tuple from sequence: tuple()

With tuple() function we can create a tuple from any sequence:

			### tuple from list:
			fruits = ["apple", "banana", "strawberry", "banana", "orange"]
			fruits_tuple = tuple(fruits)
			print(fruits_tuple)
			# ('apple', 'banana', 'strawberry', 'banana', 'orange'

			### tuple from range:
			digits = range(0, 10)
			digits_tuple = tuple(digits)
			print(digits_tuple)
			# (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

			### tuple from string:
			user_name = "ada byron"
			user_name_tuple = tuple(user_name)
			print(user_name_tuple)
			# ('a', 'd', 'a', ' ', 'b', 'y', 'r', 'o', 'n')

		

Change mutable item inside tuple? Yes!

Tuple items can not be changed!

If a tupple item is list - it will always be a list

But, we can change the items inside a list!

Change mutable item inside tuple? - example

			users = (
			    ["Ivan", "Ivanov", 34],
			    ["Maria", "Ivanova", 36],
			    ["Asen", "Asenov", 20],
			)

			### try to change items inside a mutable tuple item:
			users[0][2] = 100
			print(users[0])
			# ['Ivan', 'Ivanov', 100]

			### try to change a tupple item:
			users[0] = ["Petyr", "Petrov", 45]
			# TypeError: 'tuple' object does not support item assignment
		

Task 1

Given are two lists of names:

first_names with items "ivan", "maria", "petar"

sur_names with items "ivanov", "popova", "petrov"

Write a program which will make a third list: names, which will holds the items from the two list above as given:

			print(names)
			# ['ivan', 'maria', 'petar', 'ivanov', 'popova', 'petrov']
		

Task 2

Given are two lists first_names and sur_names as in previous task.

From first_names and sur_names create a third list:

names which will hold the items from the two list with next order:

			print(names)
			# ['ivan', 'ivanov', 'maria', 'popova', 'petar', 'petrov']
		

Task 3

Write a program which will prints out the sum of the all even numbers in the interval 1000, 1200 (both included).

			111100
		

Task 4

Given are next list of words:

			words = ["dog", "talent", "loop", "aria", "tent", "choice"]
		

Write a program which will find and output all of the words which starts and ends with same letter

			Words which starts and end with same letter are:
			talent
			aria
			tent
		

Task 5

Write a program which will ask the user to enter N names. N is also entered by the user, after respective prompt.

The names entered by the user, should be stored in a list names and will be printed to output.

Here is how your program should behave:

			How many names are you going to enter? 3
			Enter a name, please: Maria
			Enter a name, please: Ivan
			Enter a name, please: Stoyan
			******************************
			The names you've entered are:
			Maria
			Ivan
			Stoyan
		

Task 6 - page 1

Given are next list of distances from Sofia:

			distances_from_sofia = [
			    ("Bansko", 97),
			    ("Brussels", 1701),
			    ("Alexandria", 1403),
			    ("Nice", 1307),
			    ("Szeged", 469),
			    ("Dublin", 2479),
			    ("Palermo", 987),
			    ("Moscow", 1779),
			    ("Oslo", 2098),
			    ("London", 2019),
			    ("Madrid", 2259),
			]
		

Task 6 - page 2

Write a program, which will outputs only the distances from Sofia which are bellow 1500km

			Distances bellow 1500km from Sofia are:
			Bansko - 97
			Alexandria - 1403
			Nice - 1307
			Szeged - 469
			Palermo - 987
		

Task 6 - advanced

Using the sorted() function explained in Sorting HOW TO, output the sorted lists of filtered distances in ascending order:

			Bansko - 97
			Szeged - 469
			Palermo - 987
			Nice - 1307
			Alexandria - 1403