Python Interview Questions

Python Basics and Syntax

1. What are Python’s basic data types?

Python includes several basic data types: int (integers), float (floating-point numbers), str (strings), bool (booleans), and more complex types such as list, tuple, dict, and set.

2. What is the difference between a list and a tuple?

List: Mutable (can be changed after creation), defined with square brackets ([]).
Tuple: Immutable (cannot be changed after creation), defined with parentheses (()).

3. What are Python's control flow statements?

Python provides conditional statements like if, else, elif, and loop statements like for and while. The break, continue, and pass statements control loop behavior.

4. What is the purpose of the pass statement in Python?

Pass is a placeholder used where syntax requires a statement but you do not want to perform any action. It’s useful for defining empty functions or classes.

5. How do you define a function in Python?

Functions are defined with the def keyword followed by the function name and parameters. Example:
def greet(name):

print(f”Hello, {name}”)

6. Explain the difference between is and ==.

== compares the values of two objects, while is checks whether two objects refer to the same location in memory.

7. What is the difference between None, False, and 0 in Python?

None represents no value or null. False is a boolean value, and 0 is an integer. In boolean contexts, all three are considered False.

8. What is a lambda function in Python?

A lambda function is an anonymous, short function defined using the lambda keyword. Example:

add = lambda x, y: x + y

9. What is a Python module?

A module is a file containing Python definitions and statements. You can import modules using the import statement to reuse code.

10. How does Python handle exceptions?

Python uses try, except, else, and finally blocks for exception handling. try tests code for exceptions, except catches them, and finally ensures that certain code runs regardless of exceptions.

Python Data Structures (Lists, Tuples, Sets, Dictionaries)

1. What is a list in Python?

A list is an ordered, mutable collection of items, defined using square brackets ([]).

Example:
my_list = [1, 2, 3]

2. How do you modify a list in Python?

Lists are mutable, and you can modify elements via indexing or using methods like .append(), .insert(), .remove(), .pop(), etc.

3. What is the difference between a list and a tuple?

A list is mutable, whereas a tuple is immutable. This means you can modify the elements of a list but cannot change the contents of a tuple.

4. What is a dictionary in Python?

A dictionary is an unordered collection of key-value pairs, where keys are unique. It is defined using curly braces ({}), like my_dict = {“name”: “John”, “age”: 30}.

5. How can you retrieve values from a dictionary?

You can access dictionary values using their keys, like my_dict[“name”], or by using .get() which returns None if the key doesn’t exist.

6. What is a set in Python?

A set is an unordered collection of unique elements, defined using curly braces ({}).

Example:
my_set = {1, 2, 3}

7. How can you add and remove elements from a set?

Use .add() to add an element and .remove() to remove an element from a set.

Example:
my_set.add(4)

my_set.remove(1)

8. What is the difference between a set and a dictionary?

A set stores only unique values, while a dictionary stores key-value pairs, where the keys must be unique.

9. What are list comprehensions in Python?

List comprehensions provide a concise way to create lists in one line.

Example:

squares = [x**2 for x in range(5)] # Output: [0, 1, 4, 9, 16]

10. How do you merge two dictionaries in Python?

You can merge dictionaries using update() or the unpacking ** syntax in Python 3.5+:
dict1 = {“a”: 1, “b”: 2}

dict2 = {“c”: 3}

dict1.update(dict2) # dict1 becomes {‘a’: 1, ‘b’: 2, ‘c’: 3}

Python Object-Oriented Programming (OOP)

1. What are classes and objects in Python?

A class is a blueprint for creating objects (instances). Objects are instances of classes, which contain attributes (data) and methods (functions).
class Dog:

def __init__(self, name, age):

self.name = name

self.age = age

2. What is inheritance in Python?

Inheritance allows one class to inherit methods and attributes from another class. This promotes code reuse.

Example:
class Animal:

def speak(self):

print(“Animal speaks”)

class Dog(Animal):

def bark(self):

print(“Dog barks”)

3. What is polymorphism in Python?

Polymorphism means having many forms. It allows a method in different classes to have different behaviors. It allows methods to be used interchangeably based on their signature.

4. What is encapsulation in Python?

Encapsulation is the concept of bundling data and the methods that operate on the data within one unit (class). It also restricts access to certain components using access modifiers (e.g., private attributes).

5. What is the self keyword in Python?

Self refers to the instance of the class. It is used to access variables and methods associated with the class.

6. What is method overriding in Python?

Method overriding allows a subclass to provide a specific implementation of a method that is already defined in its superclass.

7. What is method overloading in Python?

Unlike other languages, Python does not support method overloading by default. However, you can simulate overloading by checking the number of arguments or types in the method.

8. What is the purpose of __init__ method?

__init__ is the constructor method in Python, called when an object is instantiated. It initializes the attributes of the class.

9. What is the difference between __str__ and __repr__ methods?

__str__ returns a user-friendly string representation of an object, while __repr__ returns a formal string representation that could be used to recreate the object.

10. What is multiple inheritance in Python?

Multiple inheritance is the ability of a class to inherit from more than one parent class. Python handles this using the C3 linearization algorithm to resolve method conflicts.

Python Functions and Modules

1. What is a function in Python?

A function in Python is a block of reusable code designed to perform a single, related action. Functions help in structuring code and avoiding redundancy. They are defined using the def keyword, followed by the function name and parentheses containing parameters.

2. What are positional arguments in Python functions?

Positional arguments are the arguments that are passed to a function in the correct positional order. The function will match the arguments with the parameters based on their position.

3. What are default arguments in Python functions?

Default arguments allow you to define default values for function parameters. If no argument is passed for that parameter, the default value is used.
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def greet(name=”Guest”):

print(f”Hello, {name}”)

4. What is variable-length argument list in Python?

Python allows passing a variable number of arguments using *args (for non-keyword arguments) and **kwargs (for keyword arguments). *args is used for passing a list or tuple, and **kwargs is used for passing a dictionary.
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def func(*args, **kwargs):

print(args)

print(kwargs)

5. What is a Python module?

A Python module is a file that contains a collection of related functions and variables. Modules are used to organize Python code. They are imported into other Python scripts using the import keyword.

6. What is the difference between import and from import in Python?

import module_name imports the entire module, and you can access its functions and variables by prefixing them with the module name. from module_name import function_name imports a specific function or variable directly, which can be used without the module name prefix.

7. What are built-in functions in Python?

Python provides several built-in functions like print(), len(), type(), sum(), min(), max(), and others, which can be used directly without any need for importing external libraries.

8. What is the purpose of the return statement in Python?

The return statement is used to exit a function and optionally pass an expression back to the caller. It terminates the function’s execution and gives a result.

9. What is the purpose of the global keyword in Python?

The global keyword is used to declare a variable as global, meaning it can be accessed and modified outside the current function or scope. Without global, any variable assignment inside a function creates a local variable.

10. What is the __name__ variable in Python?

__name__ is a special built-in variable that represents the name of the module. If the script is run directly, __name__ is set to “__main__”. This is often used to include code that should only execute when the file is run directly (not when it is imported as a module).

Python File Handling

1. How do you open a file in Python?

Files can be opened in Python using the built-in open() function, which requires the filename and an optional mode parameter (‘r’, ‘w’, ‘a’, etc.).
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file = open(“myfile.txt”, “r”)

2. What are the different file modes in Python?

Common file modes include:

- ‘r’: Read (default mode).
- ‘w’: Write (creates a new file or truncates an existing file).
- ‘a’: Append (adds content to the end of the file).
- ‘b’: Binary mode (used with other modes like ‘rb’, ‘wb’).

3. How can you read a file in Python?

You can read the entire content of a file using the read() method or read line-by-line using readline() or readlines().
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content = file.read()

4. What is the purpose of the with statement in Python file handling?

The with statement ensures that a file is properly opened and closed after use. It automatically takes care of closing the file, even if an exception occurs within the block.
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with open(“myfile.txt”, “r”) as file:

content = file.read()

5. How can you write to a file in Python?

You can write to a file using the write() or writelines() methods. If the file doesn’t exist, Python will create it if opened in write or append mode.
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with open(“myfile.txt”, “w”) as file:

file.write(“Hello, World!”)

6. What is the seek() method in Python?

The seek() method moves the file pointer to a specified location. This is useful for rewinding a file or skipping to a certain part of the file.
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file.seek(0)

7. How do you delete a file in Python?

You can delete a file using the os.remove() function from the os module.
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import os

os.remove(“myfile.txt”)

8. How do you check if a file exists in Python?

You can check if a file exists using the os.path.exists() function.
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import os

if os.path.exists(“myfile.txt”):

print(“File exists.”)

9. How do you read large files efficiently in Python?

For large files, it’s better to read line-by-line using readline() or readlines() to avoid loading the entire file into memory at once.
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with open(“largefile.txt”, “r”) as file:

for line in file:

print(line)

10. How do you copy a file in Python?

You can copy a file using the shutil.copy() function from the shutil module.
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import shutil

shutil.copy(“source.txt”, “destination.txt”)

Python Libraries (NumPy, Pandas, Matplotlib)

1. What is NumPy and what are its benefits?

NumPy is a library used for numerical computing in Python. It provides support for multi-dimensional arrays, matrices, and mathematical functions to operate on these arrays. It is faster than native Python lists due to vectorization and efficient memory management.

2. What is Pandas in Python?

Pandas is a data manipulation and analysis library. It provides two main data structures: Series (1D) and DataFrame (2D), which are flexible and easy to use for handling data from various sources like CSV, Excel, SQL, etc.

3. How do you create a DataFrame in Pandas?

You can create a DataFrame using a dictionary, list, or a numpy array. Example:
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import pandas as pd

data = {“name”: [“John”, “Alice”], “age”: [25, 30]}

df = pd.DataFrame(data)

4. What are the basic operations that can be performed on a NumPy array?

Basic operations include element-wise arithmetic operations, reshaping, slicing, indexing, and broadcasting for operations between arrays of different shapes.

5. How do you handle missing data in Pandas?

Pandas provides functions like .isna(), .dropna(), .fillna(), and .replace() for handling missing or NaN values.

6. What is the difference between loc[] and iloc[] in Pandas?

loc[] is label-based indexing, where you access rows/columns by their labels, while iloc[] is integer-location based indexing, where you access by row/column number.

7. How do you plot graphs using Matplotlib?

Matplotlib is a plotting library. You can plot graphs by using plt.plot() to plot lines, plt.bar() for bar charts, plt.hist() for histograms, and other plotting functions.
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import matplotlib.pyplot as plt

plt.plot([1, 2, 3], [4, 5, 6])

plt.show()

8. What are the differences between lists and NumPy arrays?

NumPy arrays are more efficient for numerical computations due to their homogeneity (same data type for all elements), whereas lists can hold items of different data types and are less optimized for numerical operations.

9. How do you merge two DataFrames in Pandas?

You can merge DataFrames using the merge() function, which works similarly to SQL joins. Example:
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pd.merge(df1, df2, on=”column_name”, how=”inner”)

10. What are vectorized operations in NumPy and why are they important?

Vectorized operations allow for efficient computation by applying an operation to an entire array without the need for explicit loops. This leads to faster execution as NumPy leverages low-level optimization.

Python Regular Expressions

1. What is a regular expression in Python?

A regular expression (regex) is a sequence of characters that form a search pattern. It is used for matching strings, extracting substrings, and replacing parts of strings. In Python, the re module provides support for regular expressions.

2. What is the syntax for using regular expressions in Python?

Regular expressions are used in Python with the re module, which provides methods like search(), match(), findall(), and sub().

For example, to find a match, you would use:

import re

pattern = r”\d+” # Match one or more digits

result = re.search(pattern, “The price is 100 dollars”)

3. What is the difference between search() and match() in Python?

The search() method searches the entire string for a match to the pattern, while match() checks if the pattern matches at the beginning of the string.

re.search(“pattern”, string) returns a match object if the pattern is found anywhere in the string.
re.match(“pattern”, string) only returns a match if the pattern appears at the start of the string.

4. What is a variable-length argument list in Python?

You can use the findall() method to find all occurrences of a pattern.

For example, to extract digits:
import re

text = “The year is 2024, and the month is 12”

digits = re.findall(r”\d+”, text) # Find all sequences of digits

print(digits) # Output: [‘2024′, ’12’]

5. What does the \d symbol represent in regular expressions?

The \d symbol in a regex pattern represents any digit, equivalent to [0-9]. It can be used to match single digits in a string.

6. How can you replace all occurrences of a pattern in a string with a new substring?

The sub() method allows replacing parts of a string that match a pattern. For example, to replace all digits with #:
import re

text = “Phone number: 123-456-7890”

result = re.sub(r”\d”, “#”, text)

print(result) # Output: Phone number: ###-###-####

7. What is the purpose of \b in regular expressions?

\b represents a word boundary in regular expressions. It is used to match the position where a word begins or ends. For example, r”\bword\b” matches the word “word” but not “wording”.

8. How do you use quantifiers in regular expressions?

Quantifiers specify how many instances of a pattern should be matched. Some common quantifiers are:

- *: Matches 0 or more occurrences.
- +: Matches 1 or more occurrences.
- ?: Matches 0 or 1 occurrence.
- {n,m}: Matches between n and m occurrences. Example:

re.match(r”\d{2,4}”, “12345”) # Matches 2 to 4 digits

9. What is the difference between . and \w in regular expressions?

The . (dot) matches any character except a newline, whereas \w matches any word character (letters, digits, and underscores). For example:
- r”.” matches any single character.

r”\w” matches any alphanumeric character and underscore.

10. How can you validate an email address using regular expressions in Python?

To validate an email, you can use a regex pattern that checks for the basic structure of an email address. A simple regex for validating an email is:

import re

email_pattern = r”^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$”

email = “[email protected]”

if re.match(email_pattern, email):

print(“Valid email”)

else:

print(“Invalid email”)

Python Libraries and Frameworks

1. What are some popular libraries in Python?

Libraries like NumPy, Pandas, Matplotlib, and Scikit-learn are widely used for numerical computing, data manipulation, visualization, and machine learning.

2. What is Pandas used for in Python?

Pandas is used for data manipulation and analysis, providing DataFrame and Series data structures.

3. What is the purpose of NumPy in Python?

NumPy provides support for large, multi-dimensional arrays and matrices, along with a collection of mathematical functions.

4. How do you install Python libraries?

Use pip install <library_name> to install libraries via the Python package index.

5. What is the difference between list and array in Python?

Lists are built-in Python objects, while arrays (from the array module or numpy) are used for more efficient numerical computation.

6. What is the matplotlib library used for?

matplotlib is a plotting library used for creating static, interactive, and animated visualizations.

7. What is the difference between Seaborn and Matplotlib?

Seaborn is built on top of Matplotlib and provides a high-level interface for creating attractive and informative statistical graphics

8. What is Flask used for in Python?

Flask is a micro web framework for building web applications, providing tools for routing, templates, and HTTP handling.

9. What is Django used for in Python?

Django is a high-level web framework that promotes rapid development and clean, pragmatic design for building complex web applications.

10. What is TensorFlow used for in Python?

TensorFlow is an open-source machine learning framework used for building and training deep learning models.

Python Basics and Syntax

Python Data Structures (Lists, Tuples, Sets, Dictionaries)

Python Object-Oriented Programming (OOP)

Python Functions and Modules

Python File Handling

Python Libraries (NumPy, Pandas, Matplotlib)

Python Regular Expressions

Python Libraries and Frameworks

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