Using global variables when importing functions

Question

import openpyxl as pyxl
from functions import myFunction

wb = pyxl.load_workbook("data.xlsx")
myDF = pd.DataFrame(columns=cols, index=rows)

The code below works, when I pass in the workbook and dataframe

myFunction(wb, myDF)

but if it doesn't work if I declare global variables within the import function, getting an error of 'NameError: name 'wb' is not defined.' so I don't believe it's recognising the global variable from the main script. Any ideas of what I'm doing wrong?

#from the imported code
myFunction():
  global wb
  global myDF
  ws = wb['Sheet1']

#run from the main script
myFunction()

Not sure if I get what you're saying: So, the variables wb and myDF are in the same file as myFunction? If not, did you import them into the same file? — Patrick Klein
– Patrick Klein, Commented Apr 7, 2022 at 15:54
wb and myDF come from the global scope where myFunction is defined, not the one where it is called. "Global" is a bit of a misnomer, in that every module has its own global scope; the only program-wide scope in Python is the built-in scope (which is effectively a read-only scope; you cannot add names to it). — chepner
– chepner, Commented Apr 7, 2022 at 15:57
Because global means module global. When you do from module import x that creates a new variable x in the module doing the importing, but global modifications in the imported module affect module.x. here's the good news: this is a good thing and the approach you were trying to take is an antipattern to begin with — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Apr 7, 2022 at 15:58
Don't use that approach. Don't use global. Use parameters and return values like every experienced programmer. — Matthias
– Matthias, Commented Apr 7, 2022 at 16:01

Pepe N O · Accepted Answer · 2022-04-07 17:28:53Z

1

Globals in Python are global to a module, not across all modules. as explained in this answer Visibility of global variables in imported modules

So you have to put this code inside your functions in order to work:

import openpyxl as pyxl
import pandas as pd

wb = pyxl.load_workbook("data.xlsx")
cols=['A','B'] #for example purposes
rows=range(1,10) #for example purposes
myDF = pd.DataFrame(columns=cols, index=rows)

def myFunction(): 
    global wb
    global myDF
    ws = wb['Sheet1']

And in your main module

from functions import myFunction

myFunction()

edited Apr 7, 2022 at 17:28

answered Apr 7, 2022 at 16:26

Pepe N O

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