Algorithms Programming with Python Module 1 – Python basics

PowerPoint Presentation Algorithms Programming with Python Module 1 – Python basics – Lesson 8 Nguyễn Chí ThứcList 2 • A list is a se.PowerPoint Presentation Algorithms Programming with Python Module 1 – Python basics – Lesson 8 Nguyễn Chí ThứcList 2 • A list is a se.

Algorithms & Programming with Python Module – Python basics – Lesson Nguyễn Chí Thức gthuc.nguyen@gmail.com 0986636879 List • A list is a sequence of elements numbered from (just as characters in the string) • The list can be set manually by enumerating of the elements the list in square brackets, like here: Primes = [2, 3, 5, 7, 11, 13] Rainbow = ['Red', 'Orange', 'Yellow', 'Green', 'Blue', 'Indigo', 'Violet'] List Primes = [2, 3, 5, 7, 11, 13] Rainbow = ['Red', 'Orange', 'Yellow', 'Green', 'Blue', 'Indigo', 'Violet'] • The list Primes has elements, namely: Primes[0] == 2, Primes[1] == 3, Primes[2] == 5, Primes[3] == 7, Primes[4] == 11, Primes[5] == 13 • The list Rainbow has elements, each of which is the string Length of the list Primes = [2, 3, 5, 7, 11, 13] • Length of the list: len(Primes) == • The list elements can also have negative index (start from last element): Primes[-1] == 13, Primes[-6] == Elements of list Unlike strings, the elements of a list are changeable: Rainbow = ['Red', 'Orange', 'Yellow', 'Green', 'Blue', 'Indigo', 'Violet'] print(Rainbow[0]) Rainbow[0] = 'red' for i in range(len(Rainbow)): print(Rainbow[i]) Adding element to the end of a list Using append() function: a = [] # start an empty list n = int(input()) # read number of elements for i in range(n): new_element = int(input()) # read next element a.append(new_element) # add it to the list print(a) List concatenation (addition) & repetition (multiplying) a = [1, 2, 3] b = [4, 5] c = a + b # d = b * # print([7, 8] + [9]) # print([0, 1] * 3) # [1, [4, [7, [0, 2, 5, 8, 1, 3, 4, 5] 4, 5, 4, 5] 9] 0, 1, 0, 1] Reading a list with predefined length a = [0] * int(input()) for i in range(len(a)): a[i] = int(input()) Loop through elements of list a = [1, 2, 3, 4, 5] for i in range(len(a)): print(a[i], end=' ') for elem in a: print(elem, end=' ') Quiz s = 'ab12c59p7dq' digits = [] for symbol in s: if '1234567890'.find(symbol) != -1: digits.append(int(symbol)) print(digits) 10 String’s split() and join() a = '11.03.2018'.split('.') print(a) # ['11', '03', '2018'] b = "/".join(a) # 11/03/2018 11 Input a list of value in one line (separated by spaces) # the input is a string # s = input() # s == '1 3' a = s.split() print(a) # ['1', '2', '3'] for i in range(len(a)): a[i] = int(a[i]) print(a) # [1, 2, 3] 12 Input a list of value in one line – using generator a = [int(s) for s in input().split()] print(a) 13 Display list of strings in one line a = ['red', 'green', 'blue'] print(' '.join(a)) # red green blue print(''.join(a)) # redgreenblue print('**'.join(a)) # red**green**blue 14 Display list of numbers in one line a = [1, 2, 3] # print(' '.join(a))  ERROR print(' '.join([str(i) for i in a])) # OK # 123 15 Generators Generators are used to fill a list according to a formula: [expression for variable in sequence] a = [0 for i in range(5)] print(a) # [0, 0, 0, 0, 0] 16 Generators Generators are used to fill a list according to a formula: [expression for variable in sequence] n = a = [i ** for i in range(1, n + 1)] print(a) # what is the output? 17 Generators Generators are used to fill a list according to a formula: [expression for variable in sequence] n = a = [i ** for i in range(1, n + 1)] print(a) # [1, 4, 9, 16, 25] 18 Slices Slicing with lists is similar to that with strings: • A[i:j] slice j-i elements A[i], A[i+1], , A[j-1] • A[i:j:-1] slice i-j elements A[i], A[i-1], • • ., A[j+1] A[i:j:k] cut with the step k: A[i], A[i+k], A[i+2*k] • If k