Python Revision Tour

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
In python, literal values have fixed memory locations and variable names reference them as values. This means that, although we can change the value of an integer variable, the process involves creating a new integer object with the updated value. Literal values, such as 10, have fixed memory locations, and variables act as references to these values. When we assign a new value to an integer variable, we are essentially creating a new object, and the variable now points to this new object. Hence, both Assertion and Reason are true and Reason is the correct explanation of Assertion.

(c)

Assertion is true but Reason is false.

Explanation
A string literal is a sequence of characters surrounded by single or double or triple single quotes or triple double quotes.

(d)

Assertion is false but Reason is true.

Explanation
if is conditional statement and for is loop statement. Python is case sensitive and its selection and looping statements are in lower case.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
if is conditional statement and for is loop statement. Python is case sensitive and its selection and looping statements are in lower case.

(e)

Both Assertion and Reason are false.

Explanation
In python, the break statement can be used with iteration statements only. Using break with conditional statements will result in syntax error — SyntaxError: 'break' outside loop

(e)

Both Assertion and Reason are false.

Explanation
In python, the break statement can be used with iteration statements only. Using break with conditional statements will result in syntax error — SyntaxError: 'break' outside loop

2nd_day

Reason — Variable names cannot begin with a number, although they can contain numbers.

break

Reason — break is a reserved keyword.

eval

Reason — eval is not a keyword in python.

in

Reason — in is a keyword in python.

Class

Reason — Class is not a core data type.

x**y

Reason — ** is an arithmetic operator used for exponentiation.

27

Reason — According to operator precedence remainder (%) operation will be done first and then addition (+) will be done.

14 + 13 % 15
= 14 + 13
= 27

0

Reason — According to operator precedence, floor division (//) and remainder (%) both have equal precedence hence the expression will be evaluated from left to right.

A % B // A
= 16 % 15 // 16
= 1 // 16
= 0

15

Reason — According to operator precedence, division will be done first followed by addition and then it will convert to integer.

x = int(13.25 + 4/2)
x = int(13.25 + 2.0)
x = int(15.45)
x = 15

(8/4)/2

Reason — As both the operators are division operators, the expression will be evaluated from left to right.

8/4/2 = 2/2 = 1.0
(8/4)/2
= 2/2
= 1.0

**

Reason — ** has highest precedence.

int('12.5')

Reason — int() are positive or negative whole numbers with no decimal point.

print("hello\\example\\test.txt")

Reason — Escape sequence (\\) is used for Backslash (\).

String

Reason — The input() function always returns a value of String type.

%, +

Reason — %, + are arithmetic operators.

print('Eina\nMina\nDika')

Reason —

1. print('''Eina
   \nMina
   \nDika''') — It is a multiline string and by adding \n extra line will be added.
2. print('''EinaMinaDika''') — There is no new line character.
3. print('Eina\nMina\nDika') — It adds new line by \n new line character.
4. print('Eina
   Mina
   Dika') — It creates an error because it is a multiline string with no triple quotes.

//

Reason — // is valid arithmetic operator in Python.

ECM

Reason — The slicing will start from index 1 and return at every alternative step.

s[1] = E
s[3] = C
s[5] = M
output = ECM

in

Reason — in is a membership operator.

("One")

Reason — ("One") is a string data type.

True

Reason — int(x) explicitly converts variable x to integer type.

True

Reason — Parentheses has first precedence then multiplication then division has precedence.

4/(3*(2-1))
= 4/(3*1)
= 4/3
= 1.33333

4/3*(2-1)
= 4/3*1
= 4/3
= 1.33333

False

Reason — Parentheses has first precedence then multiplication then division has precedence.

4/(3*(4-2))
= 4/(3*2)
= 4/6
= 0.6666

4/3*(4-2)
= 4/3*2
= 1.3333*2
= 2.6666

False

Reason — The expression 2**2**3 is evaluated as: 2**(2**3) because exponentiation operates from right to left (i.e., it is right associative).

True

Reason — A string literal is a sequence of characters surrounded by single or double or triple double quotes or triple single quotes.

False

Reason — Python supports dynamic typing i.e., a variable can hold values of different types at different times.

False

Reason — Variables represent labelled storage locations, whose values can be manipulated during program run.

False

Reason — Loops in Python can have else clause too.

True

Reason — Loops in Python can have else clause.

False

Reason — In nested loops, a break statement will terminate the very loop it appears in.

The smallest individual unit in a program is known as a Token. Python has following tokens:

1. Keywords — Examples are import, for, in, while, etc.
2. Identifiers — Examples are MyFile, _DS, DATE_9_7_77, etc.
3. Literals — Examples are "abc", 5, 28.5, etc.
4. Operators — Examples are +, -, >, or, etc.
5. Punctuators — ' " # () etc.

Keywords are reserved words carrying special meaning and purpose to the language compiler/interpreter. For example, if, elif, etc. are keywords. Identifiers are user defined names for different parts of the program like variables, objects, classes, functions, etc. Identifiers are not reserved. They can have letters, digits and underscore. They must begin with either a letter or underscore. For example, _chk, chess, trail, etc.

Literals are data items that have a fixed value. The different types of literals allowed in Python are:

1. String literals
2. Numeric literals
3. Boolean literals
4. Special literal None
5. Literal collections

True.

Reason — In Python, variable declaration is implicit. This means that we don't need to explicitly declare the data type of a variable before using it. The type of a variable is determined dynamically at runtime based on the assigned value. For example:

x = 5        # x is implicitly declared as an integer
name = "Ravi"  # name is implicitly declared as a string

• Price*Qty ⇒ Contains special character *
• class ⇒ It is a keyword
• 4thCol ⇒ Begins with a digit

The invalid identifier are:

2ndName ⇒ Begins with a digit
True ⇒ It is a keyword

Real

Reason — Real is not a standard built-in data type in Python.

**

Reason — Let's go through each option and see if its valid arithmetic operator or not:

1. ? — The question mark is not a valid arithmetic operator in Python.
2. < — It is a relational operator.
3. ** — It is an arithmetic operator.
4. and — It is a logical operator.

Floating constants are represented in Python in two forms — Fractional Form and Exponent form. Examples:

1. Fractional Form — 2.0, 17.5, -13.0, -0.00625
2. Exponent form — 152E05, 1.52E07, 0.152E08, -0.172E-3

A string-literal is represented as a sequence of characters surrounded by quotes (single, double or triple quotes). String-literals in Python are implemented using Unicode.

Operators are tokens that trigger some computation/action when applied to variables and other objects in an expression. Unary plus (+), Unary minus (-), Bitwise complement (~), Logical negation (not) are a few examples of unary operators. Examples of binary operators are Addition (+), Subtraction (-), Multiplication (*), Division (/).

An expression is any legal combination of symbols that represents a value. For example, 2.9, a + 5, (3 + 5) / 4.
A statement is a programming instruction that does something i.e. some action takes place. For example:
print("Hello")
a = 15
b = a - 10

A Python program can contain various components like expressions, statements, comments, functions, blocks and indentation.

Variables are named labels whose values can be used and processed during program run. Variables are important for a program because they enable a program to process different sets of data.

True

Reason — The 'not' operator has the highest precedence, followed by 'and', which has precedence over 'or', and the evaluation proceeds from left to right.
not True and False or True
= False and False or True
= False or True
= True

A block in Python, represents a group of statements executed as a single unit. Python uses indentation to create blocks of code. Statements at same indentation level are part of same block/suite and constitute the body of the block.

Data types are used to identify the type of data a memory location can hold and the associated operations of handling it. The data that we deal with in our programs can be of many types like character, integer, real number, string, boolean, etc. hence programming languages including Python provide ways and facilities to handle all these different types of data through data types. The data types define the capabilities to handle a specific type of data such as memory space it allocates to hold a certain type of data and the range of values supported for a given data type, etc.

The names of any four data types in Python are:

1. Integer
2. String
3. List
4. Tuple

Two integer types are supported by Python. They are:

1. Integers (signed)
2. Booleans

Mutable types are those whose values can be changed in place whereas Immutable types are those that can never change their value in place.

Mutable types in Python are:

1. Lists
2. Dictionaries
3. Sets

Immutable types in Python are:

1. Integers
2. Floating-Point numbers
3. Booleans
4. Strings
5. Tuples

Three reasons to use immutable data types are:

1. Immutable data types increase the efficiency of the program as they are quicker to access than mutable data types.
2. Immutable data types helps in efficient use of memory storage as different variables containing the same value can point to the same memory location. Immutability guarantees that contents of the memory location will not change.
3. Immutable data types are thread-safe so they make it easier to parallelize the program through multi-threading.

An entry-controlled loop checks the condition at the time of entry. Only if the condition is true, the program control enters the body of the loop. In Python, for and while loops are entry-controlled loops.

The pass statement of Python is a do nothing statement i.e. empty statement or null operation statement. It is useful in scenarios where syntax of the language requires the presence of a statement but the logic of the program does not. For example,

for i in range(10):
    if i == 2:
        pass
    else:
        print("i =", i)

The corrected code is shown below:

To = 30 # Correction 1
for K in range(0,To): # Correction 2
    if K % 4 == 0: # Correction 3
        print(K * 4)
    else: # Correction 4
        print(K+3) # Correction 5

Explanation

Correction 1 — Variable should be on left side and literals should be on right side.
Correction 2 — Semi-colon was missing in the for loop syntax.
Correction 3 — if statement should be in lower case.
Correction 4 — else statement should be in lower case.
Correction 5 — Full stop should not be there at the end of print function.

(i) bool
(ii) str
(iii) list of int
(iv) int
(v) bool
(vi) list of str
(vii) str

$$
$$$$
$$$$$$

range(2,7,2) returns [2, 4, 6] as it defines a range of 2 to 6 with a step of 2. The loop iterates as below:

• For i = 2, it prints $$.
• For i = 4, it prints $$$$.
• For i = 6, it prints $$$$$$.

Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello

10 0
9 1
8 2
7 3
6 4

100
90
80
70
60
50

Inside while loop, the line x = x - 10 is decreasing x by 10 so after 5 iterations of while loop x will become 40. When x becomes 40, the condition if x < 50 becomes true so keepgoing is set to False due to which the while loop stops iterating.

This is an endless (infinite) loop that will keep printing 45 continuously.

As the loop control variable x is not updated inside the loop neither there is any break statement inside the loop so it becomes an infinite loop.

1
2
3
4
5

x will be assigned each of the values from the list one by one and that will get printed.

1
2
3
4
5
6
7
8
9

range(1,10) will generate a sequence like this [1, 2, 3, 4, 4, 5, 6, 7, 8, 9]. p will be assigned each of the values from this sequence one by one and that will get printed.

-500
-400
-300
-200
-100
0
100
200
300
400

range(-500, 500, 100) generates a sequence of numbers from -500 to 400 with each subsequent number incrementing by 100. Each number of this sequence is assigned to z one by one and then z gets printed inside the for loop.

This code generates No Output.

The x-y * 2 in range(x-y * 2) is evaluated as below:

    x - y * 2
⇒ 10 - 5 * 2
⇒ 10 - 10 [∵ * has higher precedence than -]
⇒ 0

Thus range(x-y * 2) is equivalent to range(0) which returns an empty sequence — [ ].

50

Outer loop executes 10 times. For each iteration of outer loop, inner loop executes 5 times. Thus, the statement c += 1 is executed 10 * 5 = 50 times. c is incremented by 1 in each execution so final value of c becomes 50.

%
* 
* *
* * *
%%
*
* *
* * *
%%%
*
* *
* * *

In this code, the for loop is nested inside the while loop. Outer while loop runs 3 times and prints % as per the elements in x in each iteration. For each iteration of while loop, the inner for loop executes 3 times printing * as per the elements in x.

L
A
M
P

The for loop extracts each letter of the string 'lamp' one by one and place it in variable x. Inside the loop, x is converted to uppercase and printed.

o t
n w
e o

Inside the while loop, each letter of x and y is accessed one by one and printed.

apple
pear
peach

x.split(", ") breaks up string x into a list of strings so y becomes ['apple', 'pear', 'peach']. The for loop iterates over this list and prints each string one by one.

apple
PEAR
PEACH
grapefruit

x.split(', ') breaks up string x into a list of strings so y becomes ['apple', 'pear', 'peach', 'grapefruit']. The for loop iterates over this list. apple and grapefruit are less than m (since a and g comes before m) so they are converted to lowercase and printed whereas pear and peach are converted to uppercase and printed.

9.5

According to operator precedence, exponentiation(**) will come first then division then addition.

5 + 3 ** 2 / 2
= 5 + 9 / 2
= 5 + 4.5
= 9.5

The loops execute 0 times and the code produces no output. range(-1, 7, -2) returns an empty sequence as there are no numbers that start at -1 and go till 6 decrementing by -2. Due to empty sequence, the loops don't execute.

Loop executes for 5 times.

*
*
*
*
*

range(1,3,1) returns [1, 2]. For first iteration of outer loop j is in range [0, 1] so inner loop executes twice. For second iteration of outer loop j is in range [0, 1, 2] so inner loop executes 3 times. This makes the total number of loop executions as 2 + 3 = 5.

Jay
Finished!
Riya
Finished!
Tanu
Got it!

The for loop iterates over each name in the list and prints it. If the name does not begin with the letter T, Finished! is printed after the name. If the name begins with T, break statement is executed that terminates the loop. Outside the loop, Got it! gets printed.

The loop is not infinite. To know this without running it we can analyze how n is changed inside the loop in the following way:

n = 2 * n - m

Substituting value of m from m = n - 1,

    n = 2 * n - (n - 1)
⇒ n = 2 * n - n + 1
⇒ n = 2n - n + 1
⇒ n = n + 1

Therefore, inside the loop n is incremented by 1 in each iteration. Loop condition is n < 10 and initial value of n is 5. So after 5 iterations, n will become 10 and the loop will terminate.