Переменные окружения для Python проектов

Переменные окружения для Python проектов

При разработки web-приложения или бота мы часто имеем дело с какой-либо секретной информацией, различными токенами и паролями (API-ключами, секретами веб-форм). «Хардкодить» эту информацию, а тем более сохранять в публично доступной системе контроля версий это очень плохая идея.

Конфигурационные файлы

Самый простой путь решения данной проблемы, это создание отдельного конфигурационного файла со всей чувствительной информацией и добавление его в .gitignore . Минус такого подхода в том, что в гит нужно держать ещё и шаблон конфигурационного файла и не забывать его периодически обновлять.

Переменные окружения

Более продвинутый подход, это использование переменных окружения. Переменные окружения это именованные переменные, содержащие текстовую информацию, которую могут использовать запускаемые программы. Например, чтобы запустить flask-приложение, вначале нужно указать в переменной окружения FLASK_APP имя нашего приложения:

С помощью переменных окружения можно получать различные параметры приложение и секретные ключи:

Библиотека python-dotenv

Чтобы не задавать каждый раз вручную переменные окружения при новом запуске терминала, можно воспользоваться пакетом python-dotenv. Он позволяет загружать переменные окружения из файла .env в корневом каталоге приложения.
Устанавливаем пакет:

Теперь можно создать файл .env со всеми переменными среды, которые необходимы вашему приложению. Важно, добавьте .env -файл в .gitignore , не храните его в системе контроля версий.

Этот .env-файл можно использовать для всех переменных конфигурации, но его нельзя использовать для переменных среды FLASK_APP и FLASK_DEBUG , так как они необходимы уже в процессе начальной загрузки приложения.

Утилита direnv

Переменные среды могут быть автоматически загружены при входе в папку с проектом, это особенно удобно при работе с несколькими проектами одновременно. Сделать это позволяет утилита direnv. Direnv — это менеджер переменных среды для терминала, поддерживает bash, zsh, tcsh и др. оболочки. Позволяет автоматически загружать и выгружать переменные среды в зависимости от вашего текущего каталога. Это позволяет иметь переменные среды, специфичные для каждого проекта. Перед каждым приглашением проверяется наличие файла .envrc в текущем и родительском каталогах. Если файл существует, он загружается в подшаблон bash, и все экспортированные переменные затем захватываются direnv, а затем становятся доступными для оболочки.

Далее необходимо внести изменения для настройки нашей оболочки, для bash необходимо в конец файла

/.bashrc добавить следующее и перезапустить консоль:

How to Set and Get Environment Variables in Python

To set and get environment variables in Python you can just use the os module:

Note that using getenv() or the get() method on a dictionary key will return None if the key does not exist. However, in the example with BAZ , if you reference a key in a dictionary that does not exist it will raise a KeyError .

Environment variables are useful when you want to avoid hard-coding access credentials or other variables into code. For example, you may need to pass in API credentials for an email service provider in order to send email notifications but you wouldn’t want these credentials stored in your code repository. Or perhaps you need your code to function slightly differently between your development, staging and production environments. In this case you could pass in an environment variable to tell your application what environment it’s running in. These are typical use cases for environment variables.

Storing local env variables

You should write your Python code so that it is able to access environment variables from whatever environment it is running in. This could be either your local virtual environment that you’re using for development or a service that you are hosting it on. A useful package that simplifies this process is Python Decouple, this is how you would use it.

First install Python Decouple into your local Python environment.

Once installed, create a .env file in the root of your project which you can then open up to add your environment variables.

‌You can then add your environment variables like this:

Then save (WriteOut) the file and exit nano. Your environment variables are now stored in your .env file. If you’re using git, remember to add .env to your .gitignore file so that you don’t commit this file of secrets to your code repository.

Now that you have your environment variables stored in a .env file, you can access them in your Python code like this:

The benefit of using something like the above approach is that when you deploy your application to a cloud service, you can set your environment variables using whatever method or interface the provider has and your Python code should still be able to access them. Note that it is common convention to use capital letters for names of global constants in your code.

Most cloud service providers will have a CLI or web interface that lets you configure the environment variables for your staging or production environments. For guidance in these cases you ‘ll need to refer to their documentation on how to set environment variables when using their service.

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How To Set Environment Variables In Python

In this tutorial, we will see How To Set Environment Variables In Python. To set and get environment variables in Python is the same as working with dictionaries. You need to import the os module. We can set the environment variable in Python using the os module. Let’s deep dive into how to setup env variables.

Why use Environment Variables in Python

Environment variables are very useful when you want to avoid hard-coding access credentials or other variables into code.

For instance, you may need to pass your API credentials for an email service provider to send email notifications, but you don’t want these credentials stored in your code repository. Due to environment variables, we can securely commit the files in Github repo.

Sometimes you need your code to function slightly differently between your development, staging, and production environments.

In this case, you could pass in the environment variable to tell your application what environment it’s running in.

These are the typical use cases for environment variables.

Most cloud service providers will have the CLI or web interface that lets you to configure the environment variables for your development, staging or production environments.

How To Set Environment Variables In Python

Python os module environ works as the dictionary that holds the environment variables available to the program at that moment.

The environment variables gets generated when the os module is loaded, so any further change in the env variables through other ways, such as export via Terminal, will not be reflected so, please keep in mind that.

If you run the above code, then you will get the following output.

One thing to note that using getenv() or the get() method on a dictionary key will return None if the key does not exist.

However, in the example with BAZ, if you reference a key in a dictionary that does not exist, it will raise a KeyError.

Print Current Environment Variables

If we want to print the current environment variables, then we can use the os.environ function.

See the following code.

Output

It will print all the current environment variables existing in Python.

How to check if the environment variable exists or not

We can use the if statement to check the environment variables exist or not.

Output

In the above code, we can see that TERM_SESSION_ID is defined, and we have printed its value in the console.

We can not just change any default environment variable because changing the environment variable value can have serious implications for the execution of the program.

Hence, it’s advisable first to check if the environment variable exists or not. Then it’s up to you whether you want to modify the value or not. You can always define a new environment variable and use it in your program, which is the best practice.

Set Environment Variables in Python

Setting an environment variable is just like we set the values in the Python dictionary.

Output

It is like setting the dictionary values.

This is the one way to print the Environment variables. We will see another in the next subtopic.

An environment variable key-value pair must be a string; otherwise, an error will be raised.

Get Environment Variables in Python

We can use the get() function of the environ variable.

If the environment variable is not present, then it will return None.

Output

Let’s say if we try to get the PHP version, which is not defined, and then we get None in the output.

Output

Conclusion

In every programming language, there is a concept of Environment Variables, which provides us a secure way to defined secret variables like credentials.

Finally, How To Set Environment Variables In Python Example Tutorial is over.

set environment variable in python script

I have a bash script that sets an environment variable an runs a command

Now I want to use python instead of bash, because I want to compute some of the arguments that I am passing to the command.

but always the program gives up because LD_LIBRARY_PATH is not set.

How can I fix this?

Thanks for help!

(if I export LD_LIBRARY_PATH before calling the python script everything works, but I would like python to determine the path and set the environment variable to the correct value)

4 Answers 4

Similar, in Python:

You can add elements to your environment by using

and run subprocesses in a shell (that uses your os.environ ) by using

There are many good answers here but you should avoid at all cost to pass untrusted variables to subprocess using shell=True as this is a security risk. The variables can escape to the shell and run arbitrary commands! If you just can’t avoid it at least use python3’s shlex.quote() to escape the string (if you have multiple space-separated arguments, quote each split instead of the full string).

shell=False is always the default where you pass an argument array.

Now the safe solutions.

Method #1

Change your own process’s environment — the new environment will apply to python itself and all subprocesses.

Method #2

Make a copy of the environment and pass is to the childen. You have total control over the children environment and won’t affect python’s own environment.

Method #3

Unix only: Execute env to set the environment variable. More cumbersome if you have many variables to modify and not portabe, but like #2 you retain full control over python and children environments.

Of course if var1 contain multiple space-separated argument they will now be passed as a single argument with spaces. To retain original behavior with shell=True you must compose a command array that contain the splitted string:

Environment Variables in Python – Read, Print, Set

Environment variables is the set of key-value pairs for the current user environment. They are generally set by the operating system and the current user-specific configurations. For example, in a Unix environment, the environment variables are set using the user profile i.e. .bash_profile, .bashrc, or .profile files.

Environment Variables in Python

You can think of environment variables as a dictionary, where the key is the environment variable name and the value is the environment variable value.

How to Read Environment Variables in Python

We can use Python os module “environ” property to get the dictionary of all the environment variables. When the os module is loaded by Python interpreter, the environ value is set. Any further changes in the environment variables through external programs will not get reflected in the already running Python program.

Printing all the Environment Variables in Python

The os.environ variable is a dictionary-like object. If we print it, all the environment variables name and values will get printed.

Output:

If you want to print the environment variables in a better readable way, you can print them in a for loop.

Output:

Getting Specific Environment Variable Value

Since os.environ is a dictionary object, we can get the specific environment variable value using the key.

Output: pankaj home directory is /Users/pankaj

However, this way to get the environment variable will raise KeyError if the environment variable is not present.

A better way to get the environment variable is to use the dictionary get() function. We can also specify the default value if the environment variable is not present.

How to Check if an Environment Variable Exists?

We can use the “in” operator to check if an environment variable exists or not.

Output:

How to Set Environment Variable in Python

We can set the environment variable value using the syntax: os.environ[env_var] = env_var_value

Output:

If the environment variable already exists, it will be overwritten by the new value. The environment variable will be set only for the current session of the Python interpreter. If you want to change to be permanent, then you will have to edit the user profile file in the Python program.

Conclusion

It’s very easy to work with environment variables in Python. We can read, add, and update environment variables for the current execution.

References:

Python Command Line Arguments — 3 Ways to Read/Parse

Python main function Examples

I have been working on Python for more than 5 years. I love the simplicity of the language and the plethora of libraries in all the different areas of development.