2to3 creates code using deprecated imp module

[hannob]

BPO	35570
Nosy	@terryjreedy, @benjaminp, @hannob, @tirkarthi
Superseder	bpo-21446: Update reload fixer to use importlib instead of imp

^{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 = None
closed_at = <Date 2018-12-29.02:54:45.442>
created_at = <Date 2018-12-23.12:58:37.731>
labels = ['expert-2to3']
title = '2to3 creates code using deprecated imp module'
updated_at = <Date 2018-12-29.02:54:45.440>
user = 'https://github.com/hannob'

bugs.python.org fields:

activity = <Date 2018-12-29.02:54:45.440>
actor = 'terry.reedy'
assignee = 'none'
closed = True
closed_date = <Date 2018-12-29.02:54:45.442>
closer = 'terry.reedy'
components = ['2to3 (2.x to 3.x conversion tool)']
creation = <Date 2018-12-23.12:58:37.731>
creator = 'hanno'
dependencies = []
files = []
hgrepos = []
issue_num = 35570
keywords = []
message_count = 3.0
messages = ['332390', '332395', '332692']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'benjamin.peterson', 'hanno', 'xtreak']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '21446'
type = None
url = 'https://bugs.python.org/issue35570'
versions = ['Python 3.6']

[hannob]

2to3 (in python 3.6.6) will rewrite the reload function to use the imp module. However according to [1] "Deprecated since version 3.4: The imp package is pending deprecation in favor of importlib."
Also running the code with warnings enabled will show a deprecation warning.

Example, take this minimal script:

#!/usr/bin/python
import sys
reload(sys)

Running to 2to3 ends up with:
#!/usr/bin/python
import sys
import imp
imp.reload(sys)

$ PYTHONWARNINGS=d python3 foo.py
test.py:3: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
  import imp

[1] https://docs.python.org/3/library/imp.html

[tirkarthi]

Seems this came up when the original version of fixer was added as noted in https://bugs.python.org/issue11797#msg206884 . Looking further this seems to be similar to https://bugs.python.org/issue21446 where it was fixed in 3.7 and master to use importlib.reload . Since 3.6 is having it's last bug fix release I am not sure of the backport. Adding benjamin.peterson to the issue .

[terryjreedy]

It was decided in bpo-21446 to only backport the change, labelled an enhancement, to 3.7 and it is now too late to challenge that decision as 3.6 only gets security fixes.