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Updating Variables in Files

I'm trying to change multiple variables in another file, but only one variable will get updated unless I close out and reenter the program. This is a simple version of the code:

import pyVars

def loop():
newVar = int(input('New var: '))

temp1 = newVar
temp2 = pyVars.varA
temp3 = pyVars.varB

f = open('pyVars.py', 'w')
f.close()

f = open('pyVars.py', 'a')
f.write('varA = ' + str(temp1) + 'n')
f.write('varB = ' + str(temp2) + 'n')
f.write('varC = ' + str(temp3) + 'n')
f.close()

f = open('pyVars.py')
print(f.read())
f.close()
loop()

loop()


And I get the variables from another file I created in the same folder:

varA = 0
varB = 0
varC = 0


Only varA keeps changing. How do I fix this?

varB

varC

temp2

temp3

2 Answers
2

You can use Python's clever variable swapping syntax as follows:

import pyVars

def loop():
newVar = int(input('New var: '))
pyVars.varA, pyVars.varB, pyVars.varC = newVar, pyVars.varA, pyVars.varB
with open('pyVars.py', 'rb') as f:
print(f.read())
loop()

loop()


This most probably has to do with the import statement. When you write:

import pyVars


You get varA=0, varB=0, varC=0 as copies of the pyVars variables.

No matter how many times you change the values of varA, varB, varC, whenever you try to read pyVars.varA, pyVars.varB, it is always returning 0 as that was the vaues it had imported. I initally set varA=700, varB=800, varC=900 and debugged, and on each loop, the initial values of varA was still 700. I checked the initial values by making changes to the code:

from pyVar import varA, varB, varC


While debugging, varA always returned 700, even though the actual value of varA was different in pyVars.py file.

That is also the reason why only varA is getting updated on your pyVars.py file. A is getting the input from the user, but B and C were set to the values of A and B, which were imported as 0. So they always stay as 0.

This is my understanding after fiddling with the code for more than 30 mins now. I would be happy to be corrected by someone, but nevertheless, it has been a great question/learning experience for me. Thank you!

Edit: So I have finally got it to work. It was related to the import statement. Since you are changing the source file that was imported, you will need to reload the file if you need to use the new values. Please see the code that I have changed, which works for me:

import importlib

def loop():
import pyVars
pyVars = importlib.reload(pyVars)
newVar = int(input('New var: '))

temp1 = newVar
temp2 = pyVars.varA
temp3 = pyVars.varB

f = open('pyVars.py', 'w')
f.close()

f = open('pyVars.py', 'a')
f.write('varA = ' + str(temp1) + 'n')
f.write('varB = ' + str(temp2) + 'n')
f.write('varC = ' + str(temp3) + 'n')
f.close()

f = open('pyVars.py')
print(f.read())
f.close()
loop()

loop()


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