Unless I missed it, looking at https://github.com/python/cpython/blob/main/Lib/pdb.py, https://github.com/python/cpython/blob/main/Lib/inspect.py, and https://docs.python.org/3/library/pdb.html doesn't give much of a clue how to provide sources to exec-generated code.

I may have misread, but pdb *seems* to lean on inspect.findsource which eventually excludes sources that match `^<.*>$` (like `<string>`).

Running attached test_case.py:

% python test_case.py
> <string>(4)foo()
(Pdb) l
[EOF]
(Pdb) c
inspect.getfile(<function foo at 0x10b735160>): <string>
calling inspect.findsource(<function foo at 0x10b735160>) ...
Traceback (most recent call last):
  File "/Users/matt/Documents/dev/numerary/test_case.py", line 12, in <module>
    foo()
  File "/Library/Frameworks/MacPorts-20200907/Python.framework/Versions/3.9/lib/python3.9/inspect.py", line 835, in findsource
    raise OSError('could not get source code')
OSError: could not get source code

The source code is read from a file. If there is no file you get OSError, as the docstring states.

Please treat this as a feature request to add the ability for pdb (and internals) to ingest sources for exec-generated code.

There is a solution to this: you can modify the linecache module's cache to add lines under a fake filename, which is the approach attrs takes here:
https://github.com/python-attrs/attrs/blob/9727008fd1e40bc55cdc6aee71e0f61553f33127/src/attr/_make.py#L347
However, there are several downsides. 
- That dict isn't documented or appears in __all__, so it's arguably private.
- The C implementation of traceback printing opens files directly, so this doesn't work there.
- You have to invent a unique filename, and manually remove lines from the cache if the function is later deleted.
This does affect both namedtuple and dataclasses, though it's probably not too important given how straightforward the generated code they produce is.