1. Python List Comprehension If Else
2. List Comprehension Python If Statement

List Comprehension

Introduction

We learned in the previous chapter 'Lambda Operator, Filter, Reduce and Map' that Guido van Rossum prefers list comprehensions to constructs using map, filter, reduce and lambda. In this chapter we will cover the essentials about list comprehensions. List comprehensions were added with Python 2.0. Essentially, it is Python's way of implementing a well-known notation for sets as used by mathematicians.
In mathematics the square numbers of the natural numbers are, for example, created by { x² | x ∈ ℕ } or the set of complex integers { (x,y) | x ∈ ℤ ∧ y ∈ ℤ }.
List comprehension is an elegant way to define and createlist in Python. These lists have often the qualities of sets, but are not in all casessets.
List comprehension is a complete substitute for the lambda function as well as the functionsmap(), filter() and reduce(). For most people the syntax of list comprehension is easier to be grasped.

A list comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions. Introduction to List Comprehensions Python Comprehension is a way of building a code block for defining, calling and performing operations on a series of values/ data elements. Python is a simple object oriented programming language widely used for web based application development process, which grants a variety of list comprehension methods.

• List Comprehensions – HackerRank Solution in Python Let’s learn about list comprehensions! You are given three integers and representing the dimensions of a cuboid along with an integer. Print a list of all possible coordinates given by on a 3D grid where the sum of is not equal to.
• Here is an example that shows how conditionals can be written inside a list comprehension: X = 1.5, 2.3, 4.4, 5.4, 'n', 1.5, 5.1, 'a' # Original list # Extract non-strings from X to new list Xnonstr = el for el in X if not isinstance(el, str) # When using only 'if', put 'for' in the beginning.
• A list comprehension is an elegant, concise way to define and create a list in Python. The code is written in a much easier-to-read format. Python List Comprehensions consist of square brackets containing an expression, which is executed for each element in an iterable.

Examples

In the chapter on lambda and map() we had designed a map() function to convert Celsius valuesinto Fahrenheit and vice versa. It looks like this with list comprehension:The following list comprehension creates the Pythagorean triples:Cross product of two sets:

Generator Comprehension

Generator comprehensions were introduced with Python 2.6. They are simply a generator expression with a parenthesis - round brackets - around it.Otherwise, the syntax and the way of working is like list comprehension, but a generator comprehensionreturns a generator instead of a list.

A more Demanding Example

Calculation of the prime numbers between 1 and 100 using the sieve of Eratosthenes:We want to bring the previous example into more general form, so that we can calculate the list of primenumbers up to an arbitrary number n:If we have a look at the content of no_primes, we can see that we have a problem. There are lots of double entries contained in this list:The solution to this intolerable problem comes with the set comprehension, which we will cover in the next section.

Set Comprehension

A set comprehension is similar to a list comprehension, but returns a set and not a list.Syntactically, we use curly brackets instead of square brackets to create a set.Set comprehension is the right functionality to solve our problem from the previous subsection. We are able to create the set of non primes without doublets:

Recursive Function to Calculate the Primes

The following Python script uses a recursive function to calculate the prime numbers. It incorporates thefact that it is enough to examine the multiples of the prime numbers up to the square root of n:

Let’s learn about list comprehensions! You are given three integers and representing the dimensions of a cuboid along with an integer . Print a list of all possible coordinates given by on a 3D grid where the sum of is not equal to . Here, . Please use list comprehensions rather than multiple loops, as a learning exercise.

Example

All permutations of are:

Print an array of the elements that do not sum to .

Input Format

Four integers and , each on a separate line.

Constraints

Print the list in lexicographic increasing order.

Python List Comprehension If Else

Sample Input 0

Sample Output 0

Explanation 0

List Comprehension Python If Statement

Each variable and will have values of or . All permutations of lists in the form .
Remove all arrays that sum to to leave only the valid permutations.

Sample Input 1

Sample Output 1

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