Turtledemo: stop reloading demos

[terryjreedy]

BPO	22051
Nosy	@terryjreedy

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = <Date 2018-06-29.03:46:27.284>
created_at = <Date 2014-07-23.19:57:46.928>
labels = ['type-bug']
title = 'Turtledemo: stop reloading demos'
updated_at = <Date 2018-06-29.03:46:27.283>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2018-06-29.03:46:27.283>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2018-06-29.03:46:27.284>
closer = 'terry.reedy'
components = []
creation = <Date 2014-07-23.19:57:46.928>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 22051
keywords = ['patch']
message_count = 2.0
messages = ['223771', '226335']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'gregorlingl', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue22051'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']

[terryjreedy]

I propose to remove the following two lines with 'reload' from turtledemo.__main__.py.

from importlib import reload
...
... def loadfile(self, filename):
...
        reload(self.module)

Reloading modules each time a demo is run allows and even encourages module level code that initializes variables (other than classes) and has system side-effects. In particular, some such calls created the test problems reported in bpo-21882. Code that needs to be run each time the required main() is called should be inside main. Indeed, reforming the two_canvases demo (see patch for bpo-21882) made two_canvases work properly within the demo driver.

With the demos patched, I tried them all twice after commenting out the reload. I did not notice any difference, except possibly faster response.

I already edited the help text to tell users to initialize in main().

[python-dev]

New changeset b76d854f580e by Terry Jan Reedy in branch '2.7':
Issue bpo-22051: remove unneeded reload that allowed bad code.
http://hg.python.org/cpython/rev/b76d854f580e

New changeset 55d4f6c2be2d by Terry Jan Reedy in branch '3.4':
Issue bpo-22051: remove unneeded reload that allowed bad code.
http://hg.python.org/cpython/rev/55d4f6c2be2d