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I recently made the switch from python 2 to python 3. Python 3 documentation reads: "Removed reload(). Use imp.reload()" It doesn't really say why though.

This question describes how it's done now in python 3. Does anyone have any idea why it's been removed from the built-ins and now requires imp or importlib to reload? When testing a program as you build it using the interactive prompt, having reload right there by default is super convenient. Obviously I can get that back by doing something like 

from imp import reload

It's just another line of code every time I open an interactive prompt to test code. What's the reasoning behind this change?

Community
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horta
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  • It is must less universal or important the remaining built-ins. Being handy in one specific context of execution does not change this. – user2864740 Jul 05 '15 at 20:30
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    I think it was because too many people saw it sitting there in builtins and used it without understanding its limitations. Putting it in a module made it less likely that people would use it without knowing what they were doing. I can't find a reliable source for this info though. – BrenBarn Jul 05 '15 at 20:36

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reload() was removed from the built-ins as one of the Python Regrets Guido expressed in a Keynote address at OSCON 2002 (slide 6). See PEP 3100 - Miscellaneous Python 3.0 Plans which names several changes that trace their origin to that talk.

From the slide I'd say he expected exec() to be used; that'd certainly cover the most common usecase of iteratively developing some code in an editor and re-testing it in an interactive interpreter.

However, when discussing PEP 3121 - Extension Module Initialization and Finalization Guido quickly found out that he missed the function:

Yes; I'm not certain whether module reloading continues to be supported in Py3k or not. If not, it should be removed from the PEP, if yes, it should be specified.

I'm already missing the reload() builtin, so I think it should be kept around in some form. I expect some form of reload functionality will remain available, perhaps somewhere in the imp module.

So, in short, reload() was removed first, then when it was missed, imp.reload() was added. It didn't really need to be a built-in anyway, I certainly use it only rarely.

In Python 3.4 the function was moved to importlib.reload().

Martijn Pieters
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    Note that `reload` was [recently moved](http://bugs.python.org/issue18193) to `importlib`, so if you are writing new code targetting current versions, you should use `importlib.reload` directly to avoid later problems when the function eventually becomes officially deprecated and later removed. – poke Jul 05 '15 at 21:09