1. What is the Python language?
Python is one of the general-purpose and high-level programming languages. It is a dynamically typed language that provides simple syntax. It is easy to learn and offers good readability to codes.
Python is an interpreted language, meaning that it executes code line by line at runtime, without the need for a separate compilation step.
Moreover, Python is a language that comes with built-in data structures and dynamic binding. That's why it supports developers in building robust applications quickly.
2. Why is Python known as an interpreted language?
Generally, Python codes are interpreted first and then executed by the interpreter at the runtime directly. The interpreter executes the source codes line by line. This is the reason why Python is known as the interpreted language.
3. Name the various built-in data types of Python.
Python has several built-in data types that are commonly used in programming. Here are some of the fundamental ones -
- Numeric type which includes an integer, float, and complex numbers.
- Dictionary
- Set
- Boolean
- Sequence type includes string, tuple, list
4. What is the role of the _init_ method in Python?
The _init_ method in Python is a special method that is automatically called when an object is created from a class. It is commonly known as the constructor method. The primary purpose of the _init_ method is to initialise the attributes (or variables) of an object.
5. What do you understand about unit tests in Python?
Unit tests are codes written to test individual pieces of code such as functions, and classes. Python uses two frameworks to perform unit tests: PyTest and unit tests.
6. How do you create a class in Python?
In Python, a class can be created by using the keyword 'class' followed by 'class name'.
Below is an example of a class in Python -
class ClassName:
# Class attribute
7. How is a new modifier different from an override modifier?
The new modifier directs the compiler to use the new implementation. On the other side, an override modifier overrides a base function. Note that it occurs inside a child's class.
8. How will you identify a missing value in a Pandas DataFrame?
We can use the isna( ) or isnull( ) function to check whether any value is missing in a pandas DataFrame. This function returns a Boolean value if any value is missing in a Pandas column.
Example:
Input :
import pandas as pd
data = {'Name': ['John', 'Jane', None, 'Mike'],
'Age': [25, 30, None, 35],
'City': ['New York', 'London', None, 'Paris']}
df = pd.DataFrame(data)
# Identify missing values using isnull()
missing_values = df.isnull()
print(missing_values)
Output :
Name Age City
0 False False False
1 False False False
2 True True True
3 False False False
9. How can you delete rows and columns from a DataFrame?
We can delete rows and columns from a DataFrame using the drop() method. The drop() method allows you to remove specific rows or columns by specifying their indices.
Example :
Input :
import pandas as pd
data = {
'Name': ['John', 'Jane', 'Mike', 'Emily'],
'Age': [25, 30, 35, 28],
'City': ['New York','London','Paris','Tokyo']}
df = pd.DataFrame(data)
# Delete rows with index 1 and 3
df = df.drop([1, 3], axis=0)
print(df)
Output :
Name Age City
0 John 25 New York
2 Mike 35 Paris
10. Define subquery and name its types.
A subquery is nothing but a query nested inside a query or statement. The statements can be SELECT, UPDATE, INSERT, DELETE, etc.
Further, subqueries can be present inside the WHERE, HAVING, and FROM clauses. Another essential thing is that we can directly perform operations on specific rows with subqueries.
Here is a list of different subqueries used in SQL.
- Single row subquery
- Multiple column subquery
- Correlated subquery
- Multiple row subquery
- Nested subquery
11. What do you mean by view in SQL?
A view is a virtual table that we can create based on the results of a SQL statement. Like tables, a view consists of multiple rows and columns. The rows and columns of a view are essentially the rows and columns of one or more tables stored in a database.
We can create a view using the CREATE VIEW statement. Below is an example of the same.
CREATE VIEW view_name AS
SELECT column1, column2, column3,...
FROM table_name
WHERE condition;
12. What is an implicit cursor?
An implicit cursor is usually generated when we perform operations such as DELETE, INSERT, and UPDATE in databases. Besides, this cursor is used for internal processing.
13. What is the use of collation in SQL server?
Collations are nothing but a set of rules that we use to access, store, and compare data. They direct the database engine on handling the character data efficiently. Know that we can find collations on servers as well as databases.
14. What is the role of the recursive stored procedure?
The role of a recursive stored procedure is to execute a sequence of statements repeatedly until a certain condition is met. It allows you to perform iterative operations and solve problems that require repetitive logic or hierarchical data processing.
15. Is SQL a programming language?
SQL is not a general-purpose language (GPL) but a domain-specific language. It means we can use SQL to query and manage databases. As it is a domain-specific language (DSL), we can use SQL to solve only specific problems. We must note that we cannot use SQL to build applications.
16. Compare a unique key with a primary key.
| Unique Key |
Primary Key |
| Unique key acts as a unique identifier in the absence of a primary key. |
It acts as a unique identifier for all rows in a table. |
| By default, it generates a non-clustered index. |
By default, it generates a clustered index. |
| There can be one or more unique keys for a table. |
There can be a single primary key for every table. |
| We can alter the values of a unique key. |
We cannot change the values of a primary key. |
| It doesn’t support auto-incrementing values. |
It supports auto-incrementing values. |
| It accepts NULL values. |
It doesn’t take NULL values. |
17. Distinguish MySQL and SQL.
| MySQL |
SQL |
| It is a software that uses SQL as a query language. |
It is a query language. |
| It is open-source software. |
It is not an open-source tool. |
| It works on all platforms perfectly. |
It works well with Windows. But it doesn’t work perfectly with Linux and macOS. |
| It supports different storage engines. |
It helps only a single storage engine for making multiple operations. |
| It doesn't support XML and user-defined functions. |
SQL supports them. |
18. How is BETWEEN operator different from IN operator in SQL?
When it comes to the BETWEEN operator, it returns all the data that lies between two values. The value can be a text, number, etc.
The syntax for the BETWEEN operator is given as follows -
SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;
However, the IN operator returns only the specified data. In other words, it retrieves a set of records that match the given values.
The IN operator's syntax is given as follows -
SELECT column_name(s)
FROM table_name
WHERE column_name IN (list_of_values);
19. Why do we use the DISTINCT keyword in SQL?
We use the DISTINCT statement to remove duplicate values from the result set of a SQL statement. Simply put, it returns only distinct values of the result set.
Generally, the DISTINCT keyword is used along with the SELECT keyword. It can also be used with aggregate statements such as COUNT, MAX, AVG, etc.
The main thing about this keyword is that it acts on a single column only.
20. Briefly describe garbage collection in Java.
It is the automatic memory management system used in Java. Generally, Java programs create objects on the heap while running on the JVM. The objects will be used by programs as and when required. However, some of the objects will remain unused. Garbage collectors delete unused objects and free up memory space.
21. What do you mean by Java Daemon Thread?
Daemon Thread in Java is a low-priority thread that does many background operations, such as action listeners, garbage collection, etc. In a way, a daemon thread is a 'service provide thread' that supports user threads extensively. The main thing is that the lifespan of this thread depends on the user threads. Once all the user threads are executed, the JVM terminates the daemon thread immediately.
22. What are the default values assigned to instance variables in Java?
The default value is zero for numbers. It is false for Boolean. Further, it is NULL for object references.
It is essential to note that the default values are assigned within a constructor.
23. Mention the different ways to create threads in Java.
We can create threads in Java in the following ways.
- By using a runnable interface. Also, we can create them overriding the run ( ) method. After that, we need to generate thread objects.
- We can also create threads by extending the thread class. This is because the thread class provides methods and constructors with which we can operate on threads.
24. What is a composition in Java, and list its uses?
It is a design technique used in Java to implement the 'has-a' relationship in classes. It is achieved with the help of instance variables. And these variables typically refer to objects. In composition, one object is contained in another object. Mainly, one object cannot exist without the other.
Following are the uses of composition -
- It supports multiple inheritances.
- It encourages the reuse of codes.
- We can change member objects at runtime.
25. Why doesn't Java use pointers?
Below are the reasons why Java doesn't use pointers -
- Pointers consume more memory
- Memory is directly accessed if we use pointers. It will raise security issues.
