Recursion is a concept that refers to itself in its operation. This is found in all artistic fields: literature (mise en abyme), painting, photography …
A physical world example would be to place two parallel mirrors facing each other. Any object in between them would be reflected recursively.
We use recursion every day when we define words! Indeed, we use words to define others, themselves being defined by other words!
In programming, it’s a function that refers to itself. Two functions can call each other, this is called mutual recursion. Let’s use an example from the world of mathematics: factorials. A factorial of a natural number
n is the product of strictly positive integers less than or equal to
n! and calculated as follows:
n! = (n-1)!*n.
def recursive_factorial(n): return n*recursive_factorial(n-1) view raw recursive1.py hosted with ❤ by GitHub
Run this algorithm in your head, you will find that it never stops and that it runs endlessly. Indeed, if we execute the function with
n = 3
recursive_factorial(n) will be called with
n = 3, then
n = 2, then
n = 1, then
n = 0, then
n = -1, etc.
An algorithm that never stops is a problem, you can imagine!
The solution is therefore to specify a stop condition, which will always depend on our problem. In our case
3! = 3*2*1. You notice that the different factors (3, 2, and 1) are never negative nor even equal to 0. It is precisely this condition which will serve us as a stop condition: “the factor must never be neither less nor equal to 0 “. So, we add a conditional statement:
def recursive_factorial(n): if n <= 1: return 1 else: return n*recursive_factorial(n-1) view raw recursive2.py hosted with ❤ by GitHub
Calling a function inside itself is named a recursive call.
A recursive call must be in a conditional statement.
**Note: **Every recursion can be converted into iteration.
def iterative_factorial(n): f = 1 for i in range(2, n+1): f *= i return f view raw iterativeEquivalent.py hosted with ❤ by GitHub
1. Representation of the binary tree structure:A binary tree is a data structure formed by a hierarchy of elements called nodes. A node is characterized by two categories of information:
A binary tree is always designated by a node: its initial node called root.
Each node has at most two child nodes:
A branch of the tree is a path from the root of the tree to a leaf.So, a binary tree is a recursive structure since the left child and the right child are themselves nodes (representing trees in turn).
Welcome to my Blog, In this article, we will learn python lambda function, Map function, and filter function.
Lambda function in python: Lambda is a one line anonymous function and lambda takes any number of arguments but can only have one expression and python lambda syntax is
Syntax: x = lambda arguments : expression
Now i will show you some python lambda function examples:
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Welcome to my Blog , In this article, you are going to learn the top 10 python tips and tricks.
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Python is awesome, it’s one of the easiest languages with simple and intuitive syntax but wait, have you ever thought that there might ways to write your python code simpler?
In this tutorial, you’re going to learn a variety of Python tricks that you can use to write your Python code in a more readable and efficient way like a pro.
Swapping value in Python
Instead of creating a temporary variable to hold the value of the one while swapping, you can do this instead
>>> FirstName = "kalebu" >>> LastName = "Jordan" >>> FirstName, LastName = LastName, FirstName >>> print(FirstName, LastName) ('Jordan', 'kalebu')
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Today you’re going to learn how to use Python programming in a way that can ultimately save a lot of space on your drive by removing all the duplicates.
In many situations you may find yourself having duplicates files on your disk and but when it comes to tracking and checking them manually it can tedious.
Heres a solution
Instead of tracking throughout your disk to see if there is a duplicate, you can automate the process using coding, by writing a program to recursively track through the disk and remove all the found duplicates and that’s what this article is about.
But How do we do it?
If we were to read the whole file and then compare it to the rest of the files recursively through the given directory it will take a very long time, then how do we do it?
The answer is hashing, with hashing can generate a given string of letters and numbers which act as the identity of a given file and if we find any other file with the same identity we gonna delete it.
There’s a variety of hashing algorithms out there such as
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Magic Methods are the special methods which gives us the ability to access built in syntactical features such as ‘<’, ‘>’, ‘==’, ‘+’ etc…
You must have worked with such methods without knowing them to be as magic methods. Magic methods can be identified with their names which start with __ and ends with __ like init, call, str etc. These methods are also called Dunder Methods, because of their name starting and ending with Double Underscore (Dunder).
Now there are a number of such special methods, which you might have come across too, in Python. We will just be taking an example of a few of them to understand how they work and how we can use them.
class AnyClass: def __init__(): print("Init called on its own") obj = AnyClass()
The first example is _init, _and as the name suggests, it is used for initializing objects. Init method is called on its own, ie. whenever an object is created for the class, the init method is called on its own.
The output of the above code will be given below. Note how we did not call the init method and it got invoked as we created an object for class AnyClass.
Init called on its own
Let’s move to some other example, add gives us the ability to access the built in syntax feature of the character +. Let’s see how,
class AnyClass: def __init__(self, var): self.some_var = var def __add__(self, other_obj): print("Calling the add method") return self.some_var + other_obj.some_var obj1 = AnyClass(5) obj2 = AnyClass(6) obj1 + obj2
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