Python get elements from set

How to access elements in a Set

In this article, we will learn to access elements in a set in Python. We will use some built-in functions, some simple approaches, and some custom codes as well to better understand the topic. Let’s first have a quick look over what is a set in Python.

Python Sets

Python Set is a built-in data type. It is a collection of unordered data values. An unordered dataset leads to unindexed values. Set values cannot be accessed using index numbers as we did in the list. Set values are immutable which means we cannot alter the values after their creation. Data inside the set can be of any type say, integer, string, or float value. For example,

Access Elements of a Set

Reading elements of a set in Python basically means accessing one or multiple elements of the set. We know that set values are unordered which means the user is not sure of the order in which data values appear. Therefore, it is unindexed. We cannot access the elements of a set using an index say, set[0] . It will not print the 0th index value, instead, it will return an error. In this article, we will learn to access one or more elements and observe the following outputs.

Let us look at the below examples and learn what are the different ways to read elements of a given set.

Example: Accessing Using a loop and in operator

This example uses a loop to iterate over the elements of a set and checks for elements using in operator. As the set does not have indexes, we can access elements using a loop and perform operations over it.

#input set set1 = #Access element using for loop print("\nReading elements of the set: ") for x in set1: print(x)

Reading elements of the set:
3
4
5
6
11
12

Example: Accessing Using in Operator

To check for a specified value in a set, we can use the in operator. It will return True if that value is in the set else it will return False.

#input set set1 = #check for an element print("apple" in set1) print("watermelon" in set1) 

Example: Accessing Using iter and next keyword

This method uses iter to create an iterator object and with the help of next() , it prints the first item of the given input set.

#input set set1 = x = next(iter(set1)) #prints first item print(x) 

Note: Generally, the set is converted to a list using the list keyword list(set), and then the reading of set items takes place.

Conclusion

In this article, we learned to read elements of a set by using a loop, in operator, and keywords like next and iter . We used some custom codes as well. We learned that set is an unindexed data type and does not access elements using the index.

Источник

Python Set

Summary: in this tutorial, you’ll learn about Python Set type and how to use it effectively.

Introduction to the Python Set type

A Python set is an unordered list of immutable elements. It means:

• Elements in a set are unordered.
• Elements in a set are unique. A set doesn’t allow duplicate elements.
• Elements in a set cannot be changed. For example, they can be numbers, strings, and tuples, but cannot be lists or dictionaries.

To define a set in Python, you use the curly brace <> . For example:

skills = 'Python programming','Databases', 'Software design'>Code language: JavaScript (javascript)

Note a dictionary also uses curly braces, but its elements are key-value pairs.

To define an empty set, you cannot use the curly braces like this:

…because it defines an empty dictionary.

Therefore, you need to use the built-in set() function:

empty_set = set()Code language: JavaScript (javascript)

An empty set evaluates to False in Boolean context. For example:

skills = set() if not skills: print('Empty sets are falsy') Code language: PHP (php)

Empty sets are falsy Code language: PHP (php)

In fact, you can pass an iterable to the set() function to create a set. For example, you can pass a list, which is an iterable, to the set() function like this:

skills = set(['Problem solving','Critical Thinking']) print(skills)Code language: PHP (php)

'Critical Thinking', 'Problem solving'>Code language: JavaScript (javascript)

Note that the original order of elements may not be preserved.

If an iterable has duplicate elements, the set() function will remove them. For example:

characters = set('letter') print(characters)Code language: PHP (php)

'r', 'l', 't', 'e'> Code language: JavaScript (javascript)

In this example, the string ‘letter’ has two e and t characters and the set() removes each of them.

Getting sizes of a set

To get the number of elements in a set, you use the built-in len() function.

len(set) Code language: JavaScript (javascript)

ratings = 1, 2, 3, 4, 5> size = len(ratings) print(size) Code language: PHP (php)

Checking if an element is in a set

To check if a set contains an element, you use the in operator:

element in setCode language: JavaScript (javascript)

The in operator returns True if the set contains the element. Otherwise, it returns False . For example:

ratings = 1, 2, 3, 4, 5> rating = 1 if rating in ratings: print(f'The set contains ')Code language: PHP (php)

The set contains 1Code language: JavaScript (javascript)

To negate the in operator, you use the not operator. For example:

ratings = 1, 2, 3, 4, 5> rating = 6 if rating not in ratings: print(f'The set does not contain ') Code language: PHP (php)

The set does not contain 6Code language: JavaScript (javascript)

Adding elements to a set

To add an element to a set, you use the add() method:

set.add(element) Code language: JavaScript (javascript)

skills = 'Python programming', 'Software design'> skills.add('Problem solving') print(skills) Code language: PHP (php)

'Problem solving', 'Software design', 'Python programming'> Code language: JavaScript (javascript)

Removing an element from a set

To remove an element from a set, you use the remove() method:

set.remove(element) Code language: JavaScript (javascript)

skills = 'Problem solving', 'Software design', 'Python programming'> skills.remove('Software design') print(skills)Code language: PHP (php)

'Problem solving', 'Python programming'>Code language: JavaScript (javascript)

If you remove an element that doesn’t exist in a set, you’ll get an error ( KeyError ). For example:

skills = 'Problem solving', 'Software design', 'Python programming'> skills.remove('Java') Code language: JavaScript (javascript)

KeyError: 'Java'Code language: JavaScript (javascript)

To avoid the error, you should use the in operator to check if an element is in the set before removing it:

skills = 'Problem solving', 'Software design', 'Python programming'> if 'Java' in skills: skills.remove('Java') Code language: JavaScript (javascript)

To make it more convenient, the set has the discard() method that allows you to remove an element. And it doesn’t raise an error if the element is not in the list:

set.discard(element) Code language: JavaScript (javascript)

skills = 'Problem solving', 'Software design', 'Python programming'> skills.discard('Java') Code language: JavaScript (javascript)

Returning an element from a set

To remove and return an element from a set, you use the pop() method.

Since the elements in a set have no specific order, the pop() method removes an unspecified element from a set.

If you execute the following code multiple times, it’ll show a different value each time:

skills = 'Problem solving', 'Software design', 'Python programming'> skill = skills.pop() print(skill) Code language: PHP (php)

Removing all elements from a set

To remove all elements from a set, you use the clear() method:

set.clear() Code language: JavaScript (javascript)

skills = 'Problem solving', 'Software design', 'Python programming'> skills.clear() print(skills) Code language: PHP (php)

set() Code language: JavaScript (javascript)

Frozen a set

To make a set immutable, you use the built-in function called frozenset() . The frozenset() returns a new immutable set from an existing one. For example:

skills = 'Problem solving', 'Software design', 'Python programming'> skills = frozenset(skills) Code language: JavaScript (javascript)

After that, if you attempt to modify elements of the set, you’ll get an error:

skills.add('Django') Code language: JavaScript (javascript)

AttributeError: 'frozenset' object has no attribute 'add'Code language: JavaScript (javascript)

Looping through set elements

Since a set is an iterable, you can use a for loop to iterate over its elements. For example:

skills = 'Problem solving', 'Software design', 'Python programming'> for skill in skills: print(skill) Code language: PHP (php)

Software design Python programming Problem solving

To access the index of the current element inside the loop, you can use the built-in enumerate() function:

skills = 'Problem solving', 'Software design', 'Python programming'> for index, skill in enumerate(skills): print(f".") Code language: PHP (php)

0.Software design 1.Python programming 2.Problem solvingCode language: CSS (css)

By default, the index starts at zero. To change this, you pass the starting value to the second argument of the enumerate() function. For example:

skills = 'Problem solving', 'Software design', 'Python programming'> for index, skill in enumerate(skills, 1): print(f".")Code language: PHP (php)

1.Python programming 2.Problem solving 3.Software designCode language: CSS (css)

Notice that every time you run the code, you’ll get the set elements in a different order.

In the next tutorial, you’ll learn how to perform useful operations on sets such as:

Summary

Источник

Getting Started with Python Sets and Python Set Operations

Estamos traduciendo nuestros guías y tutoriales al Español. Es posible que usted esté viendo una traducción generada automáticamente. Estamos trabajando con traductores profesionales para verificar las traducciones de nuestro sitio web. Este proyecto es un trabajo en curso.

Pythons sets are unordered collections modeled on mathematical sets, in which elements are unique. Python sets support the logical operations of mathematical sets, like union, intersection, and difference. This example code declares a new set and adds the elements of a second set to it, showing that the updated set contains unique elements:

• What Python sets are and what kinds of elements they can contain
• How to fetch an element from a Python set, check if an element exists in a set, and iterate through the elements of a set.
• How to create a Python set with set literals, the set() constructor function, and the set comprehension syntax.
• How to add elements to and remove elements from Python sets
• How to combine sets with the union, intersection, difference, and symmetric difference Python set operations.
• How to compare Python sets with the subset, superset, and disjoint relationships.

What Are Sets in Python?

In Python, a set is an unordered, mutable collection of unique elements. Mathematical set operations like union, intersection, and difference can be performed on them. Two different sets can be compared with the subset, superset, and disjoint relations.

This example set uses the set literal syntax and contains the even integers between 2 and 8:

Sets can contain elements of different types. This set contains some integers and some strings:

The members of a set must be hashable. Hashable objects are generally immutable. Hashable objects must implement the __eq__() method, so two different hashable objects and can be compared to check if they are equal in value to each other. For example, two string objects can be compared to check if they are the same string.

Technically, a hashable object’s __hash__() function must always return the same value for the lifetime of the object, rather than the object itself being immutable. This blog post describes why, in practice, hashable objects used with sets are also immutable.

Integers and strings are built-in Python types that are hashable and can be stored in a set. Mutable container types like lists, dictionaries, and sets are not hashable, because their contents can change. A Python tuple is hashable if each of its values is hashable.

Create a Python Set

Python provides a few ways to create sets:

A Python set can be declared with the set literal syntax. A set literal consists of a comma-separated list of unique, hashable objects wrapped in curly braces.

Источник