Import functions in Python

Question

How can i import functions that make use of a variable defined in the current file?

main.py

from functions import a

x = 1

print(a())

functions.py

def a():
    return x

Error Message

Traceback (most recent call last):
  File "c:\Users\Test\.vscode\extensions\ms-python.python-2019.4.11987\pythonFiles\ptvsd_launcher.py", line 43, in <module>
    main(ptvsdArgs)
  File "c:\Users\Test\.vscode\extensions\ms-python.python-2019.4.11987\pythonFiles\lib\python\ptvsd\__main__.py", line 410, in main
    run()
  File "c:\Users\Test\.vscode\extensions\ms-python.python-2019.4.11987\pythonFiles\lib\python\ptvsd\__main__.py", line 291, in run_file
    runpy.run_path(target, run_name='__main__')
  File "C:\Users\Test\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "C:\Users\Test\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Users\Test\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "c:\Users\Test\Google Drive\Dev\Test\main.py", line 5, in <module>
    print(a())
  File "c:\Users\Test\Google Drive\Dev\Test\functions.py", line 2, in a
    return x
NameError: name 'x' is not defined

The exception you mention doesn't match the issue you're describing elsewhere. Are you sure the problem is with importing c, rather than looking up x, y or z after you complete the imports and start calling the functions? If you really are getting an ImportError, then something else is going wrong, unrelated to your global variable design issue. — Blckknght
– Blckknght, Commented Apr 27, 2019 at 23:06
better create functions which get it as argument a(x), b(y), c(z) — furas
– furas, Commented Apr 27, 2019 at 23:08
i changed the question by reducing complexity (only one function) and giving the full trace back — Lorenz
– Lorenz, Commented Apr 27, 2019 at 23:27
dont want to give the variables as arguments. in reality i have more than just three., — Lorenz
– Lorenz, Commented Apr 27, 2019 at 23:27

gmds · Accepted Answer · 2019-04-28 00:15:03Z

3

As another answer has noted, this will not work because of how Python scopes variables.

Instead, therefore, what I suggest is that you move all these variables into a separate file, e.g. constants.py:

main.py

from functions import a

print(a())

constants.py

X = 1

functions.py

from constants import X

def a():
    return X

Then, running import main prints 1.

answered Apr 28, 2019 at 0:15

gmds

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Comments

chepner · Accepted Answer · 2019-04-27 23:02:46Z

0

There are no process-wide globals, only module-level globals. a uses functions.x, not the x in whatever global scope it is called from.

import functions
from functions import a, b, c

functions.x = 1
functions.y = 2
functions.z = 3

print(a())
print(b())
print(c())

Because Python is lexically scoped, each function keeps a reference to the global scope in which it was defined. Name lookups use that scope to resolve free variables.

answered Apr 27, 2019 at 23:02

chepner

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2 Comments

Lorenz Over a year ago

there might be other imports that also use these variables. I think its not useful to write into the context of each import

chepner Over a year ago

I'm not stating a best practice: I'm describing how Python works. If you don't like it, don't use global variables.

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