IronLanguages / IronLanguages/ironpython3

Overridden method called instead of base class method

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Dominant language
C#
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Description

The following throws an exception instead of succeeding:

from io import BytesIO
f = BytesIO()
f.read()

class MyBytesIO(BytesIO):
    def read(self, n=None):
        raise Exception

f = MyBytesIO()
BytesIO.read(f)

See also https://github.com/IronLanguages/ironpython3/issues/1129 and https://github.com/IronLanguages/ironpython3/issues/1070.


Ran into this issue when trying to run:

make.ps1 test-"CPython.test_iter|IronPython.test_io_stdlib"

In this case it was causing a StackOverflowException:

from io import BytesIO
f = BytesIO()
f.read()

class MyBytesIO(BytesIO):
    def read(self, n=None):
        return super().read(n)

f = MyBytesIO()
f.read()

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the BytesIO subclass cases in the issue, then run make.ps1 test-"CPython.test_iter|IronPython.test_io_stdlib" to observe the related failure. Trace the BytesIO method dispatch and inheritance behavior in the IronPython implementation. Done means BytesIO.read(f) bypasses the override and super().read(n) no longer recurses or raises unexpectedly.

Written by the indexing model from the issue text.

Assessment

Tech stack
csharp, python
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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