Introduction
Python, like another programming language, has its personal set of quirks and nuances. One such quirk that usually stumps newbie builders is the “NameError: title ‘__file__’ isn’t outlined” error. What precisely is __file__? Why would it not be outlined in some contexts however not others?
This Byt will make it easier to perceive this error, why it happens, and find out how to repair it.
What does this error imply?
The __file__ attribute in Python is a built-in attribute that’s routinely set to the trail of the module file from which the script is loaded. This attribute is useful whenever you need to know the situation of the present script, particularly when coping with relative file paths. Nonetheless, whenever you attempt to entry __file__ within the Python interactive shell or Jupyter pocket book, you might encounter the “NameError: title ‘__file__’ isn’t outlined” error. It is because __file__ is undefined in these environments.
print(__file__)
NameError: title '__file__' isn't outlined
Accessing file in an Interactive Shell
The Python interactive shell is a good software for fast and soiled testing of code snippets. Nonetheless, it doesn’t help the __file__ attribute, as it isn’t related to any file. When you attempt to entry __file__ in an interactive shell, you’re going to get a NameError as proven above.
Be aware: If you might want to get the listing of the present script in an interactive shell, you should utilize the os module’s getcwd perform as a substitute.
Storing Code in Python Modules
One solution to get across the NameError when making an attempt to entry __file__ is by storing your code in a Python module as a substitute of working it within the interactive shell. A Python module is solely a file containing Python definitions and statements. The filename is the module title with the suffix .py added. Whenever you import a module, Python runs the code within the module and makes it accessible so that you can use.
# mymodule.py
print(__file__)
Now, when you import this module from one other script or from the interactive shell, __file__ will likely be outlined:
# another_script.py
import mymodule
/path/to/mymodule.py
Utilizing the examine Module
One other solution to get the file path in an interactive shell is through the use of the examine module. The examine module gives a number of capabilities to assist get details about dwell objects like modules, courses, strategies, capabilities, and so on. You need to use the getfile perform to get the file during which an object is outlined.
import examine
print(examine.getfile(examine.currentframe()))
This can print the file path of the present script, even when run from an interactive shell. Nonetheless, take into account that this can return <stdin> in an interactive shell for the reason that script is definitely learn from commonplace enter.
Getting the Present Working Listing with os.getcwd()
Whenever you’re coping with file paths in Python, it is usually helpful to know the present working listing. That is the listing from the place your script is being run. Python’s os module gives a way known as getcwd() that returns the present working listing as a string.
This is how you should utilize it:
import os
print(os.getcwd())
Operating this code will output one thing like:
$ python3 getcwd_example.py
/Customers/username/Paperwork/my_project
This means that the script getcwd_example.py is being run from the /Customers/username/Paperwork/my_project listing.
Get the Module Title with sys.argv
The sys module in Python gives entry to some variables used or maintained by the Python interpreter. One in all these is sys.argv, which is an inventory in Python, which accommodates the command-line arguments handed to the script. The primary merchandise on this listing, sys.argv[0], is at all times the script title itself.
Let’s have a look at it in motion:
import sys
print(sys.argv[0])
When you run this script as python3 argv_example.py, you may see:
$ python3 argv_example.py
argv_example.py
As you possibly can see, sys.argv[0] provides us the title of the script that’s presently being executed.
Definitely! This is a revised model of the part that focuses on accessing the __file__ attribute on imported modules within the context of the article title:
Accessing the __file__ Attribute on Imported Modules
Whenever you import a module, not solely are the capabilities, courses, and variables loaded into reminiscence, however sure particular attributes are additionally accessible. One such attribute is __file__, which might present data on the situation of the module’s supply file.
This is how one can entry it in a typical use-case. Suppose you could have a module named my_module positioned at /path/to/my_module.py:
# my_module.py
def hello_world():
print("Hey, world!")
You may import this module after which entry its __file__ attribute to see the trail the place the module is saved:
import my_module
print(my_module.__file__)
Whenever you run this script, you may see:
$ python3 import_example.py
/path/to/my_module.py
As you possibly can see, we had been in a position to entry the __file__ attribute of one other module, exterior of the script that’s presently being run.
Conclusion
On this Byte, we have explored a number of methods to resolve the
“NameError: title ‘__file__’ isn’t outlined” error in Python. We have discovered find out how to acquire the present working listing utilizing os.getcwd(), decide the module title utilizing sys.argv, and entry attributes on imported modules.
