How do yo handle exception in python?

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Tags:- Python

Python | Exception Handling

Python has many built-in exceptions that are raised when your program encounters an error.

Try and Except Statement – Catching Exceptions:

Try and except statements are used to catch and handle exceptions in Python. Statements that can raise exceptions are kept inside the try clause and the statements that handle the exception are written inside except clause.

a = [1, 2, 3]
    print ("Second element = %d" %(a[1]))
    # Throws error since there are only 3 elements in array
    print ("Fourth element = %d" %(a[3]))
    print ("An error occurred")

Try with Else Clause:

In python, you can also use the else clause on the try-except block which must be present after all the except clauses. The code enters the else block only if the try clause does not raise an exception.

# print the reciprocal of even numbers

    num = int(input("Enter a number: "))
    assert num % 2 == 0
    print("Not an even number!")
    reciprocal = 1/num

Python try...finally:

The try statement in Python can have an optional finally clause. This clause is executed no matter what and is generally used to release external resources. For example, we may be connected to a remote data center through the network or working with a file or a Graphical User Interface (GUI).

In all these circumstances, we must clean up the resource before the program comes to a halt whether it successfully ran or not. These actions are performed in the finally clause to guarantee the execution.

   f = open("test.txt",encoding = 'utf-8')

Raising Exception:

We can also manually raise exceptions using the raise keyword. We can optionally pass values to the exception to clarify why that exception was raised.

    raise NameError("Hi there")  # Raise Error
except NameError:
    print ("An exception")
    raise  # To determine whether the exception was raised or not


Tips and Tricks

What is pass in Python?

Python | Pass Statement

The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.


def myfunction():


How can you generate random numbers?

Python | Generate random numbers

Python provides a module called random using which we can generate random numbers. e.g: print(random.random())



We have to import a random module and call the random() method as shown below:

 import random


The random() method generates float values lying between 0 and 1 randomly.

To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)

import random



What is lambda in Python?

Python | Lambda function

A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.


lambda arguments : expression

a = lambda x,y : x+y

print(a(5, 6))

It also provides a nice way to write closures. With that power, you can do things like this.

def adder(x):
    return lambda y: x + y

add5 = adder(5)

add5(1)    #6

As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.

What is swapcase() function in the Python?

Python | swapcase() Function

It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.

string = "IT IS IN LOWERCASE."  



How to remove whitespaces from a string in Python?

Python | strip() Function | Remove whitespaces from a string 

To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.

string = "  Python " 


What is the usage of enumerate() function in Python?

Python | enumerate() Function

The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.

lst = ["A","B","C"] 
print (list(enumerate(lst)))

#[(0, 'A'), (1, 'B'), (2, 'C')]


Can you explain the filter(), map(), and reduce() functions?

Python | filter(), map(), and reduce() Functions

  • filter()  function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
    >>> set(filter(lambda x:x>4, range(7)))
    # {5, 6}


  • map() function calls the specified function for each item of an iterable and returns a list of result

    >>> set(map(lambda x:x**3, range(7)))
    # {0, 1, 64, 8, 216, 27, 125}


  • reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..

    >>> reduce(lambda x,y:y-x, [1,2,3,4,5])
    # 3

    Let’s understand this:


    Hence, 3.


What is a namedtuple?

Python | namedtuple

A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.

>>> from collections import namedtuple

>>> result=namedtuple('result','Physics Chemistry Maths') 

#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80) 

>>> Chris.Chemistry
# 92


Write a code to add the values of same keys in two different dictionaries and return a new dictionary.

We can use the Counter method from the collections module

from collections import Counter

dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}

new_dict = Counter(dict1) + Counter(dict2)

# Print: Counter({'a': 7, 'b': 7, 'c': 5})


Python In-place swapping of two numbers

 Python | In-place swapping of two numbers

>>> a, b = 10, 20
>>> print(a, b)
10 20

>>> a, b = b, a
>>> print(a, b)
20 10


Reversing a String in Python

Python | Reversing a String

>>> x = 'PythonWorld'
>>> print(x[: : -1])


Python join all items of a list to convert into a single string

Python | Join all items of a list to convert into a single string

>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training


python return multiple values from functions

Python | Return multiple values from functions

>>> def A():
	return 2, 3, 4

>>> a, b, c = A()

>>> print(a, b, c)
2 3 4


Python Print String N times

Python | Print String N times

>>> s = 'Python'
>>> n = 5

>>> print(s * n)


Python check the memory usage of an object

Python | Check the memory usage of  an object

>>> import sys
>>> x = 100

>>> print(sys.getsizeof(x))