turtle.write() causes flickering when the tracer is turned off.

[relent95]

BPO	47056
Nosy	@terryjreedy, @relent95
Files	test_anim_write.py: A sample script that reproduces the bug.

^{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 = None
created_at = <Date 2022-03-18.09:27:33.522>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = 'turtle.write() causes flickering when the tracer is turned off.'
updated_at = <Date 2022-03-21.07:02:30.149>
user = 'https://github.com/relent95'

bugs.python.org fields:

activity = <Date 2022-03-21.07:02:30.149>
actor = 'relent95'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-03-18.09:27:33.522>
creator = 'relent95'
dependencies = []
files = ['50690']
hgrepos = []
issue_num = 47056
keywords = []
message_count = 3.0
messages = ['415475', '415531', '415669']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'relent95']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47056'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[relent95]

When implementing an animation with turtle, usually the tracer is turned off via turtle.tracer(0, 0) and turtle.update() is called manually.

When the tracer is off, most of drawing functions skips update() calls on the underlying Canvas. But turtle.write() does not do that.
(See the implementation of TurtleScreenBase._write().)

This causes flickering, as can be seen when you run the attached script. (Press space key to hide/show texts.)

[terryjreedy]

On Win10, running 3.11.0a5+ from command line, upper ABC and boxes flicker when strings are displayed. (When run with from IDLE editor, there is no flicker except sometimes when moving mouse over or off title bar buttons.) (3.8 only gets security fixes.)

[relent95]

I tested on Ubuntu 20.04 with the following Python versions.

    3.8.2(repository version)
    3.11.0a5(compiled from the official tarball)

Both cases cause flickering.

[relent95]

Anyone can review the above PR?

[gpshead]

thanks!