‘How to develop Pythonic coding rather than Python coding – Logic Perspective’

1 Online Workshop on ‘How to develop Pythonic coding rather than Python coding – Logic Perspective’ 22.7.20 Day2 session 1 Dr. S.Mohideen Badhusha Sr.Professor/ CSE department Alva’s Institute Engineering and Technology Mijar, Moodbidri, Mangalore

3 Objectives of the Day 2 session 1 To acquire a basic knowledge in List and Tuple To comprehend the in-built functions and operations in List and Tuple To practice the simple programs in List and Tuple To introduce the Pythonic way of writing the code

4 Python offers a range of compound data types often referred to as sequences. List is one of the most frequently used and very versatile datatypes used in Python. Mutable object is the one which can be modified Mutable ordered sequence of items of mixed types How to create a list? Ex: L=[1,2,3,4,5] It can have any number of items and they may be of different types (integer, float, string etc.).

5 # empty list my_list = [] # list of integers my_list = [1, 2, 3] # list with mixed datatypes my_list = [1, "Hello", 3.4] Also, a list can even have another list as an item. This is called nested list. # nested list my_list = ["mouse", [8, 4, 6], ['a']]

6 List Index my_list = ['p','r','o','b','e'] print(my_list[0]) # Output: p print(my_list[2]) # Output: o print(my_list[4]) # Output: e # my_list[4.0] # Error! Only integer can be used for indexing # Nested List n_list = ["Happy", [2,0,1,5]] # Nested indexing print(n_list[0][1]) # Output: a print(n_list[1][3]) # Output: 5

7 Negative indexing Python allows negative indexing for its sequences. The index of -1 refers to the last item, -2 to the second last item and so on. my_list = ['p','r','o','b','e'] print(my_list[-1]) # Output: e print(my_list[-5]) # Output: p

8 How to slice lists in Python? my_list = ['p','r','o','g','r','a','m','i','z'] print(my_list[2:5]) # o/p: ['o', 'g', 'r'] print(my_list[:-5]) # o/p: ['p', 'r', 'o', 'g'] print(my_list[5:]) # o/p :['a','m','i','z'] print(my_list[:]) # o/p :['p','r','o','g','r','a','m','i','z'] odd = [2, 4, 6, 8] # change the 1st item odd[0] = 1 # o/p: [1, 4, 6, 8] # change 2nd to 4th items odd[1:4] = [3, 5, 7] print(odd) # Output: [1, 3, 5, 7]

9 odd = [1, 3, 5] odd.append(7) print(odd) # Output: [1, 3, 5, 7] odd.extend([9, 11, 13]) print(odd) # Output: [1, 3, 5, 7, 9, 11, 13] odd = [1, 3, 5] print(odd + [9, 7, 5]) # Output: [1, 3, 5, 9, 7, 5] print(["re"] * 3) #Output: ["re", "re", "re"] odd = [1, 9] #odd.insert(index,element added) odd.insert(1,3) print(odd) # Output: [1, 3, 9] odd[2:2] = [5, 7] print(odd) # Output: [1, 3, 5, 7, 9] my_list = ['p','r','o','b','l','e','m'] # delete one item del my_list[2] print(my_list) # Output: ['p', 'r', 'b', 'l', 'e', 'm'] # delete multiple items del my_list[1:5] print(my_list) # Output: ['p', 'm'] # delete entire list del my_list print(my_list) # Error: List not defined

10 my_list = ['p','r','o','b','l','e','m'] my_list.remove('p') print(my_list) # Output: ['r', 'o', 'b', 'l', 'e', 'm'] print(my_list.pop(1)) # Output: 'o' print(my_list) # Output: ['r', 'b', 'l', 'e', 'm'] print(my_list.pop()) # Output: 'm' print(my_list) # Output: ['r', 'b', 'l', 'e'] my_list.clear() print(my_list) # Output: []

11 my_list = [3, 8, 1, 6, 0, 8, 4] print(my_list.index(8)) # Output: 1 print(my_list.count(8)) # Output: 2 my_list.sort() print(my_list) # Output: [0, 1, 3, 4, 6, 8, 8] my_list.reverse() print(my_list) # Output: [8, 8, 6, 4, 3, 1, 0]

12 Summary of List Functions Append()- Add an element into list extend()- Add all elements of a list to the another list Insert() - Insert an item at the defined index Remove()- removes an item from the list Pop()- removes and returns an element at the given index Clear()- removes all items from the list Index()- returns the index of the first matched item Count()- returns the count of number of items passed as an argument

13 Built-in List Functions SN Function with Description 1 len(list)-Gives the total length of the list. 2 max(list)-Returns item from the list with max value. 3 min(list)-Returns item from the list with min value. 4 list(seq)-Converts a tuple into list. 5 sum(list)-Adds the all the elements in the list (elements should be numerical)

14 Lists and functions print(len(nums)) print(max(nums)) print(min(nums)) print(sum(nums)) print(sum(nums)/len(nums))#average Note: The sum() function only works when the list elements are numbers

15 Basic List Operations: Lists respond to the + and * operators much like strings; . In fact, lists respond to all of the general sequence operations we used on strings Python Expression Results Description len([1, 2, 3]) 3 Length [1, 2, 3] + [4, 5, 6] [1, 2, 3, 4, 5, 6] Concatenation ['Hi!'] * 4 ['Hi!', 'Hi!', 'Hi!', 'Hi!'] Repetition 3 in [1, 2, 3] True Membership for x in [1, 2, 3]: print x, 1 2 3 Iteration

16 List Comprehension List comprehension consists of an expression followed by for statement inside square brackets. pow2 = [2 ** x for x in range(10)] # Output: [1, 2, 4, 8, 16, 32, 64, 128, 256, 512] print(pow2) This code is equivalent to the following codes pow2 = [] for x in range(10): pow2.append(2 ** x)

17 pow2 = [2 ** x for x in range(10) if x > 5] print(pow2) #output : [64, 128, 256, 512] odd = [x for x in range(20) if x % 2 == 1] print(odd) #output : [1, 3, 5, 7, 9, 11, 13, 15, 17, 19] my_list = ['p','r','o','b','l','e','m'] print('p' in my_list) # Output: True print('a' in my_list) # Output: False print('c' not in my_list) # Output: True

18 What is tuple? In Python programming, a tuple is similar to a list. The difference between the two is that we cannot change the elements of a tuple once it is assigned whereas in a list, elements can be changed. A simple immutable ordered sequence of items Items can be of mixed types, including collection types immutable object is the one which can not be modified listlist

19 Sequence Types 1. Tuple  A simple immutable ordered sequence of items  Items can be of mixed types, including collection types 1. Strings – Immutable object is the one which can not be modified – Conceptually very much like a tuple 2. List Mutable object is the one which can be modified Mutable ordered sequence of items of mixed types

20 Similar Syntax • All three sequence types (tuples, strings, and lists) share much of the same syntax and functionalities. • Key difference: – Tuples and strings are immutable – Lists are mutable • The operations shown in this section can be applied to all sequence types – most examples will just show the operation performed on one

21 Lists: Mutable >>> li = [‘abc’, 23, 4.34, 23] >>> li[1] = 45 >>> li [‘abc’, 45, 4.34, 23] • We can change lists in place. • Name li still points to the same memory reference when we’re done.

22 Tuples: Immutable >>> t = (23, ‘abc’, 4.56, (2,3), ‘def’) >>> t[2] = 3.14 Traceback (most recent call last): File "<pyshell#75>", line 1, in -toplevel- tu[2] = 3.14 TypeError: object doesn't support item assignment You can’t change a tuple. You can make a fresh tuple and assign its reference to a previously used name. >>> t = (23, ‘abc’, 3.14, (2,3), ‘def’)

23 Sequence structures • Tuples are defined using parentheses (and commas). >>> tu = (23, ‘abc’, 4.56, (2,3), ‘def’) • Lists are defined using square brackets (and commas). >>> li = [“abc”, 34, 4.34, 23] • Strings are defined using quotes (“, ‘, or “““). >>> st = “Hello World” >>> st = ‘Hello World’ >>> st = “““This is a multi-line string that uses triple quotes.”””

24 Sequence access • We can access individual members of a tuple, list, or string using square bracket “array” notation. >>> tu = (23, ‘abc’, 4.56, (2,3), ‘def’) >>> tu[1] # Second item in the tuple. ‘abc’ >>> li = [“abc”, 34, 4.34, 23] >>> li[1] # Second item in the list. 34 >>> st = “Hello World” >>> st[1] # Second character in string. ‘e’

25 Positive and negative indices >>> t = (23, ‘abc’, 4.56, (2,3), ‘def’) Positive index: count from the left, starting with 0. >>> t[1] ‘abc’ Negative lookup: count from right, starting with –1. >>> t[-3] 4.56

26 Slicing Operations >>> t = (23, ‘abc’, 4.56, (2,3), ‘def’) Return a copy of the container with a subset of the original members. Start copying at the first index, and stop copying before the second index. >>> t[1:4] (‘abc’, 4.56, (2,3)) You can also use negative indices when slicing. >>> t[1:-1] (‘abc’, 4.56, (2,3))

27 Slicing Operations >>> t = (23, ‘abc’, 4.56, (2,3), ‘def’) Omit the first index to make a copy starting from the beginning of the container. >>> t[:2] (23, ‘abc’) Omit the second index to make a copy starting at the first index and going to the end of the container. >>> t[2:] (4.56, (2,3), ‘def’)

28 The ‘in’ Operator • Boolean test whether a value is inside a container: >>> t = [1, 2, 4, 5] >>> 3 in t False >>> 4 in t True >>> 4 not in t False • For strings, tests for substrings >>> a = 'abcde' >>> 'c' in a True >>> 'cd' in a True >>> 'ac' in a False • Be careful: the in keyword is also used in the syntax of for loops and list comprehensions.

29 The + Operator • The + operator produces a new tuple, list, or string whose value is the concatenation of its arguments. >>> (1, 2, 3) + (4, 5, 6) (1, 2, 3, 4, 5, 6) >>> [1, 2, 3] + [4, 5, 6] [1, 2, 3, 4, 5, 6] >>> “Hello” + “ ” + “World” ‘Hello World’

30 The * Operator • The * operator produces a new tuple, list, or string that “repeats” the original content. >>> (1, 2, 3) * 3 (1, 2, 3, 1, 2, 3, 1, 2, 3) >>> [1, 2, 3] * 3 [1, 2, 3, 1, 2, 3, 1, 2, 3] >>> “Hello” * 3 ‘HelloHelloHello’

31 Concluding Tips List- mutable (changeable) Tuple – immutable ( unchangeable) list with mixed datatypes my_list = [1, "Hello", 3.4] List and Tuple starts with 0 index Extend() - a list is to be included as elements Append() - to be included as single element + is concatenation operator for list,tuple and string.

‘How to develop Pythonic coding rather than Python coding – Logic Perspective’

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