Python Data, Expressions, Statements: brief important questions and answers

1. What is the role of an interpreter? Give a detailed note on python interpreter and interactive mode of operation.

An interpreter is a computer program that executes instructions written in a programming language. It can either

·                 execute the source code directly or

·                 translates the source code in a first step into a more efficient representation and executes this code

Python interpreter and interactive mode

With the Python interactive interpreter it is easy to check Python commands. The Python interpreter can be invoked by typing the command "python" without any parameter followed by the "return" key at the shell prompt:

$ python

>>> 

Once the Python interpreter is started, you can issue any command at the command prompt ">>>".

For example,let us print the "Hello World" statement:

>>>     print "Hello World"

>>>     Hello World

In the interactive Python interpreter the print is not necessary:

>>>     "Hello World"

>>>     3

3

>>>    

Typing an end-of-file character (Ctrl+D on Unix, Ctrl+Z on Windows) at the primary prompt causes the interpreter to exit with a zero exit status. If that doesn’t work, you can exit the interpreter by typing the following command: quit().

When commands are read from a tty, the interpreter is said to be in interactive mode. In this mode it prompts for the next command with the primary prompt, usually three greater-than signs (>>>); for continuation lines it prompts with the secondary prompt, by default three dots (...). The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt:

Continuation lines are needed when entering a multi-line construct. As an example, take a look at this if statement:

>>>     the_world_is_flat = 1

>>>     if the_world_is_flat:

... print "Be careful not to fall off!"

2. List down the rules for naming the variable with example.

A variable is a name that refers to a value. An assignment statement creates new variables and gives them values:

Variable names can be arbitrarily long. They can contain both letters and numbers, but they have to begin with a letter. It is legal to use uppercase letters, but it is a good idea to begin variable names with a lowercase letter .

The underscore character, _, can appear in a name. It is often used in names with multiple words, such as my_name or variable_name.

If you give a variable an illegal name, you get a syntax error:

3. What do you mean by rule of precedence? List out the order of precedence and demonstrate in detail with example.

When more than one operator appears in an expression, the order of evaluation depends on the rules of precedence. For mathematical operators, Python follows mathematical convention. The acronym PEMDAS is a useful way to remember the rules,

•          Parentheses have the highest precedence and can be used to force an expression to evaluate in the order you want. Since expressions in parentheses are evaluated first,

2 * (3-1) is 4, and (1+1)**(5-2) is 8.

You can also use parentheses to make an expression easier to read, as in (minute * 100) / 60, even if it doesn’t change the result.

•         Exponentiation has the next highest precedence, so 2**1+1 is 3, not 4 and 3*1**3 is 3, not 27.

•                  Multiplication  and  Division  have  the  same  precedence,  which  is  higher  than  Addition  and Subtraction, which also have the same precedence. So 2*3-1 is 5, not 4, and 6+4/2 is 8, not 5.

•         Operators with the same precedence are evaluated from left to right (except exponentiation).

So in the expression degrees / 2 * pi, the division happens first and the result is multiplied by pi. To divide by 2π, you can use parentheses or write degrees / 2 / pi.

4. Explain the role of function call and function definition with example.

A function is a named sequence of statements that performs a computation. When you define a function, you specify the name and the sequence of statements. Later, you can “call” the function by name.

>>>     type(32)

<type 'int'>

The name of the function is type. The expression in parentheses is called the argument of the function. The result, for this function, is the type of the argument. A function “takes” an argument and “returns” a result. The result is called the return value.

Type conversion functions

Python provides built-in functions that convert values from one type to another. The int function takes any value and converts it to an integer, if it can, or complains otherwise:

>>>    int('32')

32

>>>    int('Hello')

ValueError: invalid literal for int(): Hello

int can convert floating-point values to integers, but it doesn’t round off; it chops off the fraction part:

>>>     int(3.99999)

3

>>>     int(-2.3)

-2

float converts integers and strings to floating-point numbers:

>>>     float(32)

32.0

>>>     float('3.14159') 3.14159

Finally, str converts its argument to a string:

>>>     str(32)

'32'

>>>     str(3.14159)

'3.14159'

5. How do you make use of math functions in Python?

Math functions

Python has a math module that provides most of the familiar mathematical functions. A module is a file that contains a collection of related functions.

Before we can use the module, we have to import it:

>>> import math

This statement creates a module object named math. If you print the module object, you get some information about it:

>>> print math

<module 'math' (built-in)>

The module object contains the functions and variables defined in the module. To access one of the functions, specify the name of the module and the name of the function, separated by a dot (also known as a period). This format is called dot notation.

>>>     ratio = signal_power / noise_power

>>>     decibels = 10 * math.log10(ratio)

>>>     radians = 0.7

>>>     height = math.sin(radians)

The first example uses log10 to compute a signal-to-noise ratio in decibels (assuming that signal_power and noise_power are defined). The math module also provides log, which computes logarithms base e.

The second example finds the sine of radians. The name of the variable is a hint that sin and the other trigonometric functions (cos, tan, etc.) take arguments in radians. To convert from degrees to radians, divide by 360 and multiply by 2π:

>>>     degrees = 45

>>>     radians = degrees / 360.0 * 2 * math.pi

>>>     math.sin(radians)

0.707106781187

The expression math.pi gets the variable pi from the math module. The value of this variable is an approximation of π, accurate to about 15 digits.

>>> math.sqrt(2) / 2.0 0.707106781187

6. Write a Python program to swap two variables.

x = 5

y = 10

# create a temporary variable and swap the values temp = x

x = y

y = temp

print("The value of x after swapping:”,x))

print("The value of y after swapping:”,y))

7. Write a Python program to check whether a given year is a leap year or not.

# To get year (integer input) from the user

year = int(input("Enter a year"))

if (year % 4) == 0:

if (year % 100) == 0:

if (year % 400) == 0:

print("%d is a leap year"%year)

else:

print("%d is not a leap year"%d)

else:

print("%d is a leap year"%year)

else:

print("%d is not a leap year"%year)

8. Write a Python program to convert celsius to fahrenheit .

(Formula: celsius * 1.8 = fahrenheit –32).

#Python Program to convert temperature in celsius to fahrenheit

#change this value for a different result

celsius = 37.5

#calculate fahrenheit

fahrenheit = (celsius * 1.8) + 32

print('%0.1f degree Celsius is equal to %0.1f degree Fahrenheit' %(celsius,fahrenheit))

Part B

1.              Explain in detail about various data types in Python with an example?

2.              Explain the different types of operators in python with an example.

3.              Discuss the need and importance of function in python.

4.              Explain in details about function prototypes in python.

5.              Discuss about the various type of arguments in python.

6.              Explain the flow of execution in user defined function with example.

7.              Illustrate a program to display different data types using variables and literal constants.

8.              Show how an input and output function is performed in python with an example.

9.              Explain in detail about the various operators in python with suitable examples.

10.        Discuss the difference between tuples and list

11.        Discuss the various operation that can be performed on a tuple and Lists (minimum 5)with an example program

12.        What is membership and identity operators.

13.        Write a program to perform addition, subtraction, multiplication, integer division, floor division and modulo division on two integer and float.

14.        Write a program to convert degree Fahrenheit to Celsius

15.        Discuss the need and importance of function in python.

16.        Illustrate a program to exchange the value of two variables with temporary variables

17.        Briefly discuss in detail about function prototyping in python. With suitable example program

18.        Analyze the difference between local and global variables.

19.        Explain with an example program to circulate the values of n variables

20.        Analyze with a program to find out the distance between two points using python.

21.        Do the Case study and perform the following operation in tuples i) Maxima minima iii)sum of two tuples iv) duplicate a tuple v)slicing operator vi) obtaining a list from a tuple vii) Compare two tuples viii)printing two tuples of different data types

22.        Write a program to find out the square root of two numbers.