Python how to import class from another file

How can i import class from another file in python?

i’m a newbee at python and i’m having this error when importing class from a file this is my directory

in my acces.py i have this (is not all the complete code)

and in my alloweds.py

and this is the error log

5 Answers 5

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That is circular depency. Create one more file, for example database.py where you import your cursor.

You have a loop when you are importing from both files. So if you have only 1 file import from the other you should be fine.

While there are quick’n’dirty technical workarounds those only mask the symptom, they don’t cure the issue itself. There are various strategies to avoid circular dependencies (like extracting the common dependency to a distinct module as in ex4’s answer), and most often you use a combination of thise. In your case, the very obvious issue is that you make your allowed module dependent on a global cursor for no good reason. What you should do here is, plain simply, to explicitely pass the dependee as argument to the depender ie:

This strategy (named «dependency injection») not only breaks the circular dependency, but also makes your code much more easily testable in isolation.

Как работают импорты в Python

Порой бывает трудно правильно реализовать import с первого раза, особенно если мы хотим добиться правильной работы на плохо совместимых между собой версиях Python 2 и Python 3. Попытаемся разобраться, что из себя представляют импорты в Python и как написать решение, которое подойдёт под обе версии языка.

Содержание

Ключевые моменты

Основные определения

Пример структуры директорий

Что делает import

Основы import и sys.path

Вот как оператор import производит поиск нужного модуля или пакета согласно документации Python:

Программы могут изменять переменную sys.path после её инициализации. Директория, содержащая запускаемый скрипт, помещается в начало поиска перед путём к стандартной библиотеке. Это значит, что скрипты в этой директории будут импортированы вместо модулей с такими же именами в стандартной библиотеке.

Кроме того, импорты в Python регистрозависимы: import Spam и import spam — разные вещи.

Функцию pkgutil.iter_modules() (Python 2 и Python 3) можно использовать, чтобы получить список всех модулей, которые можно импортировать из заданного пути:

Чуть подробнее о sys.path

Документация Python описывает sys.path так:

Список строк, указывающих пути для поиска модулей. Инициализируется из переменной окружения PYTHONPATH и директории по умолчанию, которая зависит от дистрибутива Python.

Документация к интерфейсу командной строки Python добавляет информацию о запуске скриптов из командной строки. В частности, при запуске python

Best Ways in Python to Import Classes From Another File

In this article, we will understand the need for modular programming and then will learn how to Import Classes from another file in the python programming language. We will discuss some examples to understand them more clearly. We will also understand how predefined libraries help us. So let’s get started.

Why is it needed?

So, the first question that sounds to our mind is that why we need to import any file or classes from another file? Or, Is it really important? Or, How it will affect our programming approach? Answers to all these questions are within this article.

First, understand why is it needed? In programming, we are often in situations in which we have to repeat certain operations. Writing code for them each and every time is quite a tedious task. To avoid such situations, we use the concept of Object-Oriented Programming aka OOPs.

Object Oriented Programming or OOPs

OOPs is a programming concept in which we create objects based on some defined classes having some properties (called attributes) and functions (called methods). The advantage of doing that is we can reuse it a number of times we want. We can also implement other real-time entities like inheritance ( i.e. inheriting properties from other classes), abstraction ( i.e. information hiding), polymorphism (i.e. present in many forms) e.t.c. in it. It is an independent concept in itself, so we will talk about it somewhat later. For now, move ahead and talk about modular programming.

Modular Programming

Although, OOPs is an efficient and smart way of programming, we can’t say that it themselves solve all the problems alone. Besides the core concept of OOPs, there are some other problems we face while programming. Working on real scenarios is very different from the one that we learn. In reality, solving any problem may require thousands of lines of codes which may have hundreds of functions and tens of classes. Maintaining all those functions and classes in one program is a difficult task. So we use the modular programming approach to cope with such situations.

Modular Programming is a programming approach in which rather than writing code for one big problem, we split it into several small independent problems. Once we solve each of them, we unite them to achieve our primary goal.

Advantage of using Modular Programming

The advantage of following the approach is that we can increase the readability of codes. We can reuse it a number of times. More, it is easy for us to maintain them and make changes to them according to our use. Moreover, it helps us a lot while debugging our program as we don’t have to fumble much in one file.

Introduction to Import statement

Once all independent problems are solved, the question arises that how can we associate them. Here, the Python Import statement comes into the picture.

Import statement helps in importing code from other files or modules into the file we are working on. You can think of it as a bridge that gives us access to the class attributes or methods from other files so that we can use them. However, there is a proper syntax to follow to do that which we will see in a few seconds. Before that first understand the given directory structure.

So, in the given directory structure we have an application folder that contains two folders named module1 and module2. Inside each folder, we have files named file1, file2, and file3 respectively. Now, we will discuss different scenarios of importing classes or files one by one. Here we go,

Import Classes From Another File

In this example, first, we will define a class in file1.py and then import it in file2.py.

In the above example, we imported file1 using the “import” statement. After that, we create an instance of the class we want to use i.e. ArithmeticOperations by referring to it. We can understand it as;

We can also do it using “from import ” statement. Take a look to it;

Import All classes from Another File

In this section, we will discuss that can we import all the classes at once from another file. Sometimes, it is the scenario that it is needed to import all the classes from other files. In that case, we use “from import *” statement. We can read it as from file_name import all. It means that we imported all the available classes from the given file. Let’s look at its example.

Import Classes From Another Folder

In this example, we will use ArithmeticOperations class in file3.py i.e located in another folder i.e module1. But before doing that we have to include __init__. py file in module1 which tells the interpreter that the module is within the same package.

We also have to specify the path of module1. For that, we will use the “sys” module. Let’s look at the code.

‘sys.path.insert(0,”..”) ‘ This line of code tells the interpreter that first come out of the current directory to parent directory and then look for the module there.

Import Classes From Predefined Libraries

In the above example, we used “import sys” which is a predefined library and we want to import it and use its functionalities.

sys.path.insert(); We can understand, that we want to use the insert method from the path class that is present in the sys module. Using such dependencies and modules make our works easier as we don’t need to write code for those function explicitly. We just need the knowledge of the given package and how to use it.

In this case, the issue lies within the reference of the source class you want to import. The answer to this question depends on various conditions in which you want to import the file. We have discussed all of the above and you can refer to them according to your condition.

We can use the following code in file2.py to import the class from file1 dynamically.

#__init__ method is used to import the module which takes module name as the parameter
module = __import__(module_name)

# getattr() is used to import class name form the module we imported
class_nm = getattr(module,class_name)
data= class_nm.get_sum(class_nm,3,8)
print(data)

We can import class dynamically using __import__ magic function or imp module.
See it with an example;

import imp
import sys

#dynamic import
def dynamic_imp(name, class_name):
# imp.find_module() returns the path and description of given module
fp, path, desc = imp.find_module(name)

#imp.load_module() returns either class or package
package = imp.load_module(name, fp, path, desc)
class_ = imp.load_module(«% s.% s» % (name, class_name), fp, path, desc)
return package, class

if name == “main“:
mod, modCl = dynamic_imp(“file1 “,”addNumbers”)
modCl.addNumbers(1, 2)

# Run the following command
!pip install ipynb

# You can import other notebooks using
from ipynb.fs.full. import *

Conclusion

So, today we looked at how can we import classes from other files or folders. We also gained knowledge about Modular Programming and Import Statement. We looked, Modular programming changed the approach of programming and made it easier.

I hope this article helped you. Keep supporting. Thank You!

how to import a class from another file in python

When the program is very complex, we often divide it into chunks or modules and are saved into multiple files. This reduces the complexity and makes it easy to debug or identify errors in the code. Suppose you want to use a class that is in another file. For this, you need to import that class into the file where you want to use it.

In this tutorial, we are going to discuss some methods which are used to import classes. Importing classes from other programs allows us to use them within the current program. Thus, helping in improved readability and reusability of code. Importing can be done within the same or from different folders.

If you want to learn more about python Programming, visit Python Programming Tutorials.

Some of the common ways to import a class from another file in Python are listed below

Importing a specific class by using the import command

IMPORT MULTIPLE CLASSES FROM ONE FILE USING IMPORT COMMAND

When you have multiple classes in the MyFile.py. Then instead of writing import command with every class you just have to import the file that contains the classes and in the main.py file use these classes by making their respective objects.

IMPORT All CLASSES FROM ONE FILE USING IMPORT * COMMAND

Here you just have to write an asterisk (*) with the import command i.e, import*. This command allows access to all the classes and you don’t need to write the name of the class with every function. You just have to make the object with that respective class.

IMPORT All CLASSES FROM ANOTHER FOLDER in parent directory USING IMPORT SYS COMMAND

Here Inner_Project is the folder that is holding the file of our classes. The main file is in another folder ‘Project2’ which is also the parent folder of the Inner_Project. Before importing we have to include the __init__.py file in the Inner_Project that will contain our classes to tell the interpreter that our Project is within the same package.

sys.path.insert(0,“..”) command tells the interpreter to look from the parent folder to take out the desired class.

Address: Application/Inner_Project/MyFile.py

Address: Application/Project2/main.py

IMPORTing A CLASS DYNAMICALLY

Here the __import__(module_name) command is used to import the module or file, whereas getattr() command is used to get the attributes of the class.

Python – Import a class from another File

This Article explains how to import a class from another Python file.

If you’ve been coding in Python for over a week, there’s a 9 out of 10 chance that you’ve already begun importing some libraries into your code to enhance the functionality of your code. Python would not have the world wide recognition it has now, without the existence of these libraries. But what’s the underlying concept here? How do these libraries bring these almost magical functions into your code? And more importantly, can we replicate such a feature?

Background

Before we get to the main point of this article, we’re going to quickly go over a few other things. You can skip ahead if you already know this, but for those who don’t, I highly recommend you read through all of this.

We’re not interested in what this function does, rather we’re going to be focusing on the construction of the above statement. Does it seem familiar? If you’ve done Classes in Python you’ll have noticed that this is exactly how we call methods from classes. To further illustrate me point, here is a small piece of code from our Python classes article.

Do you see how similar the two ways of calling the function are? Well, that’s because both of them are calling from classes. This part is a little complicated because numpy is a module, not a class. Then what’s a module?

A module is a way of storing reusable Python code, containing classes or functions.

The key point to take away here is that a module can have more than just one class or function. At any rate, that’s enough background. If you’re curious about anything discussed above, you can always google it later.

Creating a Module

If you’ve been following this article carefully, you must have arrived at the conclusion that we need to create a module, where we will create the class to be imported. Don’t worry, you can create a module in less than a min. All you need to do is create a Python file and give it a suitable name.

Creating a Class

We’ll now create a class in the module1.py file. There is no limit to the number of classes you can add, but for the sake of this article, well stick to one. We’ll also through in a bonus function as well (Not everything has to be in a class).

Below we’ve created a class called maths, which is clearly meant to store math related methods. We’ve created two methods, add and sub which will add and subtract two numbers respectively.

Now back to our main Python file.

Importing

It’s now time to import the module and begin trying out our new class and functions.

Importing the module as we mentioned earlier will automatically bring over every single class and function in the module into the namespace. If you’re only going to use a single function, you can prevent the namespace from being cluttered by only importing that function. We’ll demonstrate an example below.

Now you only need to use display() to call the imported function.

Creating Custom Libraries

You wonder, why bother creating our own modules when their are already so many available? The answer is custom libraries.

When you’re coding extensively, you end up having to code similar pieces of code over and over again. Let’s take GUI libraries as an example. To create a GUI, you need to write dozens of lines of code even for the simplest interface. There’s alot of repetition too, as your basically the same functions over and over again. At some point you realize that it would a better idea to create pack this code into a function and save it in a python file. Later when you want to create a GUI, you can simply call that function with a single call.

This approach is (usually) meant to be a personal one. Everyone has their own style and preferences while coding, so that’s why there is not a universal standard. You don’t really have to think about this on a basic level, but it’s something to consider once you’re more experienced.

This marks the end of the Import a class from another Python File Article. Any suggestions or contributions for CodersLegacy are more than welcome. Relevant questions about the article material can be asked in the comments section below.