On Fri., 13 Sep. 2019, 7:21 am Steven D'Aprano, <st...@pearwood.info> wrote:
> On Wed, Sep 11, 2019 at 09:34:07AM -0400, Daniel Holth wrote: > > > I didn't realize you could override __builtins__.str. That's interesting. > > Don't touch __builtins__ that's a CPython implementation detail. The > public API is to ``import builtins`` and use that. > > This override technique is called monkey-patching, it's permitted but > considered a fairly dubious thing to do in production code, since it > risks breaking other libraries or even parts of your own code which > relies on str(b'') working. > > It may be better to isolate the monkey-patch to the module (hopefully > there is only one!) that needs it, by a simple global that shadows the > built-in: > > import builtins > def str(obj): > assert not isinstance(obj, bytes) > return builtins.str(obj) > > instead of putting it into builtins itself. > In a lot of cases like this, the problems aren't with directly calling str(), but calling third party APIs that indirectly call str(). One nice thing a debugging str() monkey patch can do that the -bb command line switch can't is be selective in when it fails, by inspecting the frame stack for the modules of interest before throwing an exception. Cheers, Nick. >
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