{"id":3032,"date":"2021-11-23T16:05:23","date_gmt":"2021-11-23T16:05:23","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3032"},"modified":"2025-03-30T10:16:44","modified_gmt":"2025-03-30T10:16:44","slug":"python-private-functions","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-private-functions\/","title":{"rendered":"Python Private Functions"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to define Python private functions in a module using the __all__<\/code> variable.<\/p>\n\n\n\n

Suppose you have a module<\/a> called mail.py<\/code> with two functions<\/a> send()<\/code> and attach_file()<\/code>.<\/p>\n\n\n

def<\/span> send<\/span>(email, message)<\/span>:<\/span>\n    print(f'Sending \"{message}<\/span>\" to {email}<\/span>'<\/span>)\n\ndef<\/span> attach_file<\/span>(filename)<\/span>:<\/span>\n    print(f'Attach {filename}<\/span> to the message'<\/span>)\n   <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
And you want to expose only the send()<\/code> function to other modules, not the attach_file()<\/code> function. In other words, you want the attach_file()<\/code> function to be private and cannot be accessible from the outside of the mail module.<\/p>\n\n\n\n
Note that for simplicity, we only print out some texts in the functions.<\/p>\n\n\n\n
If other modules use the import *<\/code> statement like this:<\/p>\n\n\n
from<\/span> mail import<\/span> *<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
you can prefix a function name with an underscore (_<\/code>) to make it private. For example:<\/p>\n\n\n
def<\/span> send<\/span>(email, message)<\/span>:<\/span>\n    print(f'Sending \"{message}<\/span>\" to {email}<\/span>'<\/span>)\n\ndef<\/span> _attach_file<\/span>(filename)<\/span>:<\/span>\n    print(f'Attach {filename}<\/span> to the message'<\/span>)\n   <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
From the mail.py<\/code> file, you can use the import * from mail<\/code> module and can see only the send()<\/code> function:<\/p>\n\n\n
from<\/span> mail import<\/span> *\n\n\nsend('test@example.com'<\/span>,'Hello'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In other words, you won’t be able to access the _attach_file()<\/code> function from the main<\/code> module. If you attempt to call the _attach_file()<\/code> function, you’ll get an error.<\/p>\n\n\n\n
Another way to make the attach_file()<\/code> function private is to use the __all__<\/code> variable. In this way, you don’t need to prefix the function name with an underscore (_) to make it private.<\/p>\n\n\n\n
The __all__<\/code> specifies a list of functions (also variables, and other objects) that are available to the other modules. In other words, you can make a function private by not listing it in the __all__<\/code> variable.<\/p>\n\n\n\n
The following uses the __all__<\/code> variable in the mail<\/code> module to make the send()<\/code> function public and attach_file()<\/code> function private:<\/p>\n\n\n
# mail.py<\/span>\n\n__all__ = ['send'<\/span>]\n\ndef<\/span> send<\/span>(email, message)<\/span>:<\/span>\n    print(f'Sending \"{message}<\/span>\" to {email}<\/span>'<\/span>)\n\ndef<\/span> attach_file<\/span>(filename)<\/span>:<\/span>\n    print(f'Attach {filename}<\/span> to the message'<\/span>)\n   <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
From the main.py<\/code> module, you also cannot access the attach_file()<\/code> function like before:<\/p>\n\n\n
# main.py<\/span>\n\nfrom<\/span> mail import<\/span> *\n\n\nsend('test@example.com'<\/span>,'Hello'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
First, create a package called mail<\/code> with the __init__.py<\/code> file and create the email.py<\/code> module in the mail<\/code> package:<\/p>\n\n\n
\u251c\u2500\u2500 mail\n|  \u251c\u2500\u2500 email.py\n|  \u2514\u2500\u2500 __init__.py\n\u2514\u2500\u2500 main.py<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, place the following code in the email.py<\/code> file:<\/p>\n\n\n
# email.py<\/span>\n\n__all__ = ['send'<\/span>]\n\n\ndef<\/span> send<\/span>(email, message)<\/span>:<\/span>\n    print(f'Sending \"{message}<\/span>\" to {email}<\/span>'<\/span>)\n\n\ndef<\/span> attach_file<\/span>(filename)<\/span>:<\/span>\n    print(f'Attach {filename}<\/span> to the message'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, use the import *<\/code> and add the send()<\/code> function to the __all__<\/code> variable in the __init__.py<\/code>:<\/p>\n\n\n
from<\/span> .email import<\/span> * \n\n__all__ = email.__all__<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
By doing this, the mail<\/code> package exposes only the send()<\/code> function specified in the email.__all__<\/code> variable. It hides the attach_file()<\/code> from the outside.<\/p>\n\n\n\n
From the main.py<\/code> file, you can import the mail<\/code> package and use the send()<\/code> function like this:<\/p>\n\n\n
# main.py<\/span>\n\nimport<\/span> mail\n\n\nmail.send('test@example.com'<\/span>,'Hello'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Alternative, you can import the send()<\/code> function from the mail package:<\/p>\n\n\n
# main.py<\/span>\n\nfrom<\/span> mail import<\/span> send\n\n\nsend('test@example.com'<\/span>,'Hello'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
To make a function private in Python:<\/p>\n\n\n\n
As mentioned in the module tutorial<\/a>, the import *<\/code> is not a good practice and often leads to bugs. However, you still can utilize it by using a package<\/a>.<\/p>\n\n\n\n