IronLanguages / IronLanguages/ironpython3
Confusion between class variable and instance variable when descriptor is used
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- Dominant language
- C#
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Description
Prerequisites
- Are you running the latest version?
- Are you reporting to the correct repository?
- Did you perform a cursory search?
Description
Consider the following program:
class ListDescriptor:
def __set__(self, obj, value):
obj.__dict__["x"] = value
class Test:
x = ListDescriptor()
def __init__(self):
self.x = [1,2,3]
t = Test()
print(t.x)
The output from this program differs between CPython and IronPython.
Steps to Reproduce
- Run the above program
Expected behavior: Output should be [1, 2, 3].
Actual behavior: Output is <ListDescriptor object at 0x000000000000002B>.
Workarounds
You can work around this by explictly defining the __get__ method in ListDescriptor. However, we encountered this in third-party code that we would rather not modify if it could be avoided.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the descriptor example from the issue and compare its output with CPython. Trace IronPython's class and instance attribute lookup for descriptors, then verify that the program prints [1, 2, 3] without requiring a get workaround.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- csharp, python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100