Python Lists, Tuples, Dictionaries: short important questions and answers

LISTS, TUPLES AND DICTIONARIES

1. What is a list?

A list is an ordered set of values, where each value is identified by an index. The values that make up a list are called its elements. Lists are similar to strings, which are ordered sets of characters, except that the elements of a list can have any type.

2. Solve a)[0] * 4 and b) [1, 2, 3] * 3.

>>>  [0] * 4 [0, 0, 0, 0]

>>>     [1, 2, 3] * 3 [1, 2, 3, 1, 2, 3, 1, 2, 3]

3. Let list = [’a’, ’b’, ’c’, ’d’, ’e’, ’f’]. Find a) list[1:3] b) t[:4] c) t[3:] .

>>>     list = [’a’, ’b’, ’c’, ’d’, ’e’, ’f’]

>>>     list[1:3] [’b’, ’c’]

>>>     list[:4] [’a’, ’b’, ’c’, ’d’]

>>>     list[3:] [’d’, ’e’, ’f’]

4. Mention any 5 list methods.

append() ,extend () ,sort(), pop(),index(),insert and remove()

5. State the difference between lists and dictionary.

List is a mutable type meaning that it can be modified whereas dictionary is immutable and is a key value store. Dictionary is not ordered and it requires that the keys are hashable whereas list can store a sequence of objects in a certain order.

6. What is List mutability in Python? Give an example.

Python represents all its data as objects. Some of these objects like lists and dictionaries are mutable, i.e., their content can be changed without changing their identity. Other objects like integers, floats, strings and tuples are objects that cannot be changed. Example:

>>>     numbers = [17, 123]

>>>     numbers[1] = 5

>>>     print numbers [17, 5]

7. What is aliasing in list? Give an example.

An object with more than one reference has more than one name, then the object is said to be aliased. Example: If a refers to an object and we assign b = a, then both variables refer to the same object:

>>>     a = [1, 2, 3]

>>>     b = a

>>>     b is a True

8. Define cloning in list.

In order to modify a list and also keep a copy of the original, it is required to make a copy of the list itself, not just the reference. This process is called cloning, to avoid the ambiguity of the word “copy”.

9. Explain List parameters with an example.

Passing a list as an argument actually passes a reference to the list, not a copy of the list. For example, the function head takes a list as an argument and returns the first element:

def head(list):

return list[0]

output:

>>>     numbers = [1, 2, 3]

>>>     head(numbers)

10. Write a program in Python to delete first element from a list.

def deleteHead(list): del list[0]

Here’s how deleteHead is used:

>>>     numbers = [1, 2, 3]

>>>     deleteHead(numbers)

>>>     print numbers [2, 3]

11. Write a program in Python returns a list that contains all but the first element of the given list.

def tail(list): return list[1:]

Here’s how tail is used:

>>> numbers = [1, 2, 3]

>>> rest = tail(numbers)

print rest [2, 3]

12. What is the benefit of using tuple assignment in Python?

It is often useful to swap the values of two variables. With conventional assignments a temporary variable would be used. For example, to swap a and b:

>>>     temp = a

>>>     a = b

>>>     b = temp

This solution is cumbersome; tuple assignment is more elegant:

>>>     a, b = b, a

13. Define key-value pairs.

The elements of a dictionary appear in a comma-separated list. Each entry contains an index and a value separated by a colon. In a dictionary, the indices are called keys, so the elements are called key-value pairs.

14. Define dictionary with an example.

A dictionary is an associative array (also known as hashes). Any key of the dictionary is associated (or mapped) to a value. The values of a dictionary can be any Python data type. So dictionaries are unordered key-value-pairs.

Example:

>>> eng2sp = {}  # empty dictionary

>>>     eng2sp[’one’] = ’uno’

>>>     eng2sp[’two’] = ’dos’

15. How to return tuples as values?

A function can only return one value, but if the value is a tuple, the effect is the same as returning multiple values. For example, if we want to divide two integers and compute the quotient and remainder, it is inefficient to compute x/y and then x%y. It is better to compute them both at the same time.

>>>     t = divmod(7, 3)

>>>     print t (2, 1)

16. List two dictionary operations.

·                 Del -removes key-value pairs from a dictionary

·                 Len - returns the number of key-value pairs

17. Define dictionary methods with an example.

A method is similar to a function—it takes arguments and returns a value— but the syntax is different. For example, the keys method takes a dictionary and returns a list of the keys that appear, but instead of the function syntax keys(eng2sp), method syntax eng2sp.keys() is used.

>>>     eng2sp.keys() [’one’, ’three’, ’two’]

18. Define List Comprehension.

List comprehensions apply an arbitrary expression to items in an iterable rather than applying function. It provides a compact way of mapping a list into another list by applying a function to each of the elements of the list.

19.Write a Python program to swap two variables.

x = 5

y = 10

temp = x

x = y

y = temp

print('The value of x after swapping: {}'.format(x))

print('The value of y after swapping: {}'.format(y))

20.Write the syntax for list comprehension.

The list comprehension starts with a '[' and ']', to help us remember that the result is going to be a list. The basic syntax is [expression for item in list if conditional ].

PART - A

1.              What is slicing?

2.              How can we distinguish between tuples and lists?

3.              What will be the output of the given code?

a.               List=[‘p’,’r’,’i’,’n’,’t’,]

b.              Print list[8:]

4.              Give the syntax required to convert an integer number into string?

5.              List is mutable. Justify?

6.              Difference between del and remove methods in List?

7.              Difference between pop and remove in list?

8.              How are the values in a tuple accessed?

9.              What is a Dictionary in Python

10.        Define list comprehension

11.        Write a python program using list looping

12.        What do you meant by mutability and immutability?

13.        Define Histogram

14.        Define Tuple and show it is immutable with an example.

15.        state the difference between aliasing and cloning in list

16.        what is list cloning

17.        what is deep cloning

18.        state the difference between pop and remove method in list

19.        create tuple with single element

20.        swap two numbers without using third variable

21.        define properties of key in dictionary

22.        how can you access elements from the dictionary

23.        difference between delete and clear method in dictionary

24.        What is squeezing in list? give an example

25.        How to convert a tuple in to list

26.        How to convert a list in to tuple

27.        Create a list using list comprehension

28.        Advantage of list comprehension

29.        What is the use of map () function.

30. How can you return multiple values from function?

31. what is sorting and types of sorting

32. Find length of sequence without using library function.

33. how to pass tuple as argument

34. how to pass a list as argument

35. what is parameter and types of parameter

36. how can you insert values in to dictionary

37. what is key value pair

38. mention different data types can be used in key and value

39. what are the immutable data types available in python

40. What is the use of fromkeys() in dictioanary.