Message376465
This issue only impacts container objects where the len(repr(o)) is less than width. If the length is greater than width, containers are handled by a different code path which is covered by a unit test and works correctly.
For this case, indeed it works in Python 2 but not in Python 3. The PrettyPrinter._format code has been refactored quite a lot with respect to handling of containers.
In both Python 2 and 3 this happens:
PrettyPrinter.pprint([10]) calls
PrettyPrinter._format([10]) which calls
PrettyPrinter._repr([10]) which calls
MyPrettyPrinter.format([10]) which calls
PrettyPrinter.format([10]) which calls
_safe_repr([10]) which calls
_safe_repr(10)
returns 10
returns [10]
returns [10]
returns [10]
returns [10]
But then they diverge - in Python 3 the [10] is returned as the result, but in Python 2 there is another piece of code (starting here https://github.com/python/cpython/blob/fdda200195f9747e411d3491aae0806bc1fcd919/Lib/pprint.py#L179) which overrides this result and recalculates the representation for containers. In our case it does:
since issubclass(type([10]), list):
# ignore the [10] calculated above, now call
self._format(10) which calls
PrettyPrinter._repr(10) which calls
MyPrettyPrinter.format(10)
returns 0xa
returns 0xa
returns 0xa
returns [0xa]
This explains the difference between Python 2 and 3.
As to why the first calculation returns [10] and not [0xa]:
This is because _safe_repr is defined at module scope, so once it is called we are no longer on the PrettyPrinter instance, and the format() override is no longer accessible. When _safe_repr needs to recurse on container contents, it calls itself.
I think the solution is to make _safe_repr a method of PrettyPrinter, and make it call self.format() when it needs to recurse. The default self.format() just calls _safe_repr, so when there is no override the result is the same.
The PR's diff looks substantial, but that's mostly due to the indentation of _safe_repr code. To make it easier to review, I split it into several commits, where the indentation is done in one commit as a noop change. The other commits have much smaller diffs. |
|
Date |
User |
Action |
Args |
2020-09-06 16:31:30 | iritkatriel | set | recipients:
+ iritkatriel, doerwalter, anthonybaxter, georg.brandl, rhettinger, markhirota, mic_e, xiang.zhang |
2020-09-06 16:31:30 | iritkatriel | set | messageid: <1599409890.63.0.140743882223.issue28850@roundup.psfhosted.org> |
2020-09-06 16:31:30 | iritkatriel | link | issue28850 messages |
2020-09-06 16:31:30 | iritkatriel | create | |
|