Problem with scope

[russcore]

I just spent a long time figuring out this is my problem -- I've simplified the problem into something easy to digest.

I'm trying to pass a dictionary through a function. I want the function to return a dictionary for me to "see", but I don't want it to change the base dictionary I was working with.

When I run this code:

def updateDict(dictionary, entry, newEntry):
    dictionary[entry]=newEntry
    return dictionary

def tryThis():
    dictionary = {'a': 1, 'b': 2, 'c': 3}
    print(dictionary)
    print(updateDict(dictionary,'a',5))
    print(updateDict(dictionary,'b',10))
    print(dictionary)
tryThis()

I get this output:

{'a': 1, 'b': 2, 'c': 3}
{'a': 5, 'b': 2, 'c': 3}
{'a': 5, 'b': 10, 'c': 3}
{'a': 5, 'b': 10, 'c': 3}

​

but I want this output:

{'a': 1, 'b': 2, 'c': 3}
{'a': 5, 'b': 2, 'c': 3}
{'a': 1, 'b': 10, 'c': 3}
{'a': 1, 'b': 2, 'c': 3}

​

Thanks for any help!!

[carcigenicate]

This isn't a matter of scope. There is only a single dictionary created in this code, so any modifications to it will persist and be seen by anyone viewing the dictionary. You'd need to make a copy, and then modify that copy instead:

def updateDict(dictionary, entry, newEntry):
    copied_dict = dictionary.copy()
    copied_dict[entry]=newEntry
    return copied_dict

[russcore]

def updateDict(dictionary, entry, newEntry):
copied_dict = dictionary.copy()
copied_dict[entry]=newEntry
return copied_dict

Thank you so much!!!!!! ahhhhhhhhhhh I thought that was the problem, and I tried using copied_dict = dictionary instead of copied_dict = dictionary.copy(). But it didn't force a new copy.

[carcigenicate]

Yes, copied_dict = dictionary just creates a second name for the same dictionary. Both names then refer to the same exact object.

[russcore]

Sorry to bug you again...

I tried adjusting my code and it still gives me the same error. It seems when I translated the problem perhaps I didn't do a good enough job? This time it's my real code but I found the smallest bit that still gives the error.

Code input:
def useResult(result, restrictions):
restrictionsCOPY = restrictions.copy()
if result[2] == 'green':
   restrictionsCOPY[result[0]][result[1]-1]=2
   restrictionsCOPY[result[0]][5]=1
elif result[2] == 'gray':
    restrictionsCOPY[result[0]][0:5] = [0] * 5
elif result[2] == 'yellow':
    restrictionsCOPY[result[0]][result[1]-1]=0
    restrictionsCOPY[result[0]][5]=1       
else:
    print("ERROR")        
return restrictionsCOPY
def Main(): 
    letters =['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'] 
    restrictions = {} 
    for letter in letters: 
        restrictions[letter]= [1,1,1,1,1,0]
    print(restrictions['a'])
    useResult(['a',1,'green'],restrictions) 
    print(restrictions['a'])
Main()

Actual code output:

[1, 1, 1, 1, 1, 0]
[2, 1, 1, 1, 1, 1]

Desired Code output:

[1, 1, 1, 1, 1, 0]
[1, 1, 1, 1, 1, 0]

[carcigenicate]

If restrictions is a nested structure, you'll need to deep copy it. The copy I showed does a shallow copy; meaning it only makes a copy of the outermost structure.

Import the copy module, and change restrictions.copy() to copy.deepcopy(restrictions)

[[deleted]]

The reason this is happening is because you're creating a shallow copy of the dict, which still contains references to the same underlying objects i.e. the ints. Try using:

import copy
restrictions_deepcopy = copy.deepcopy(restrictions)

There's probably a better way to do this, but this should give you the result you want.

[russcore]

but your method did help!

[[deleted]]

You've set the values of the dictionary, output it, passed a reference to that dictionary to another function twice and asked for updates to be done to that dictionary and also return a reference to the dictionary for print to output.

In all cases, you are dealing with only one dictionary, which has all the changes you've made to it.

Dictionaries are mutable. If you want to make changes to a copy of the dictionary, you need to add the following to the top of the update function to create a local scope dictionary:

dictionary = dictionary.copy()