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DocTests for functools.cache()-decorated functions have no line number #136914
Description
Bug report
Bug description:
(edited to reflect discussion comments)
doctests of functions decorated with functools.cache (or lru_cache()) do not get their line number retrieved, e.g.:
# file /tmp/t.py
import functools
@functools.cache
def f(x):
"""cached
>>> f(1)
-2
"""
return -x$ python -m doctest /tmp/t.py
**********************************************************************
File "/tmp/t.py", line ?, in t.f
Failed example:
f(1)
Expected:
-2
Got:
-1
**********************************************************************
1 item had failures:
1 of 1 in t.f
***Test Failed*** 1 failure.where we can see that the File "..." line is missing the line number of the example.
Also:
>>> import doctest
>>> import t
>>> dt, = doctest.DocTestFinder().find(t)
>>> dt
<DocTest t.f from /home/denis/src/cpython/t.py:None (1 example)>
>>> print(dt.lineno)
NoneThis is because DocTest._find_lineno() relies on inspect.isfunction() to possibly inspect function's code and get line numbers; but inspect.isfunction() returns False for a function decorated with functools.cache because only plain types.FunctionType is considered.
Original question: Should such cached functions be considered as well in inspect.isfunction()?
I would be happy to work on a fix in case this change is acceptable.
CPython versions tested on:
CPython main branch, 3.13
Operating systems tested on:
No response
Linked PRs
- gh-136914: Use inspect.isroutine() in DocTest's lineno computation #136930
- [3.13] gh-136914: Fix support of cached functions and properties in DocTest's lineno computation (GH-136930) #137615
- [3.14] gh-136914: Fix support of cached functions and properties in DocTest's lineno computation (GH-136930) #137616
Activity
picnixz commentedon Jul 21, 2025
inspect.isfunctionhas very strict constraints and after being decorated byfunctools.cache, the object is no longer a function at runtime. So I don't think we should change anything ininspect. However we should change something indoctest.EDIT: Also, it might not necessarily be the case that the decorator is called at the same place where the function has been defined (sometimes, people write it in two steps).
cc @serhiy-storchaka
brianschubert commentedon Jul 21, 2025
For context, the was foreseen as being a possible issue in #115440 (review), but at the time it wasn't known whether a class wrapper using
functools.wraps/functools.update_wrapperwas a realistic use case. Evidently it is :-)serhiy-storchaka commentedon Jul 21, 2025
inspect.isroutine()is already used in some places ofdoctest. It should be used instead ofinspect.isfunction()in other places as well.[-]functools.cache decorated functions not handled by inspect.isfunction()[/-][+]DocTests for functools.cache()-decorated functions have no line number[/+]gh-136914: Fix support of cached functions and properties in DocTest'…
pythongh-136914: Fix support of cached functions and properties in Do…
pythongh-136914: Fix support of cached functions and properties in Do…
pythongh-136914: Fix support of cached functions and properties in Do…
[3.13] gh-136914: Fix support of cached functions and properties in D…
pythongh-136914: Fix support of cached functions and properties in Do…
[3.14] gh-136914: Fix support of cached functions and properties in D…