Python  Program to find factorial of a number
This is an example of how to find the factorial of a number in python.
The factorial of a number is a product of all the positive integers less than or equal to that number.
For example, the factorial of 5 is 5x4x3x2x1 = 120
Factorial is not defined for negative integers, and the factorial of zero is one, 0! = 1.
Check here for factorial recursive way
n = int(input('Enter no.:'))
fact = 1
for i in range(1,n+1):
fact *= i
print(fact)
Output for the above code
_{>>> ====================== RESTART: E:\py\factorial.py ====================== Enter no.:5 120}
let's modify the code to handle number less than or equal to zero
n = int(input('Enter no.:'))
fact = 1
if n < 0:
print(f"Sorry, factorial does not exist for {n}, negative number")
elif n == 0:
print("The factorial of 0 is 1")
else:
for i in range(1,n+1):
fact *= i
print(fact)
Output for the above code
_{>>> ====================== RESTART: E:\py\factorial.py ====================== Enter no.:5 120 >>> ====================== RESTART: E:\py\factorial.py ====================== Enter no.:0 The factorial of 0 is 1 >>> ====================== RESTART: E:\py\factorial.py ====================== Enter no.:5 Sorry, factorial does not exist for 5, negative number}
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():
pass
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
print(random.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
print(random.randrange(5,100,2))
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.
Syntex:
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 nonalphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
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]) builtin function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
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 pairwise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:yx, [1,2,3,4,5]) # 3
Let’s understand this:
21=1
31=2
42=2
52=3Hence, 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
#format
>>> 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(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python Inplace swapping of two numbers
Python  Inplace 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])
dlroWnohtyP
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)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python  Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28