VS Code python extension will modify my data in Python script when i debug with it

[sherlockchou86]

Environment data

• VS Code version: 1.19.3
• Extension version (available under the Extensions sidebar): 2018.4.0 (2 May 2018)
• OS and version: windows 10
• Python version (& distribution if applicable, e.g. Anaconda): python 3.5.2
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): N/A
• Relevant/affected Python packages and their versions: XXX

the VS Code IDE will modify my property in Python script when i debug with it. my test code as below

bytesIO = io.BytesIO(...)
bytesIO.seek(0)
print(bytesIO.realine()) # will output the first line

Actual behavior

print(bytesIO.readline()) output nothing.

Expected behavior

print(bytesIO.readline()) will output the first line.

if i add bytesIO.seek(0) after i watch the variable by vs code ide, the output is right. I wander if the IDE has modified the data inside the bytesIO object, such as it called its iterator and changed the position flag inside the object.

hope it helps!

[DonJayamanne]

@karthiknadig could this be related to issues we came across previously.

[karthiknadig]

This is the same issue as microsoft/ptvsd#406 . We used to call __iter__ if an object implemented it while building the repr.

[sherlockchou86]

ok, thank you!

[brettcannon]

@karthiknadig so is the iterator no longer consumed?

[karthiknadig]

If an object implements __iter__ and is NOT an instance of following collection types: list, tuple, bytearray, range, dict, set, frozenset, xrange, buffer, only then we don`t consume the iterator (while building the repr).

[brettcannon]

@karthiknadig Thanks for the clarification! I've re-classified this as a PTVSD 3 issue then.

@sherlockchou86 in case it wasn't clear, the next release of the extension should have this fixed in the experimental debugger.