__terminal__ output reappears after clearing the element

[CarstenGrohmann]

Problem

Output written to __terminal__ cannot be cleared. Clearing the target element from application code removes the rendered text only. The next print puts everything back.

Cause

__Terminal__ keeps the output history in self.buffer and rewrites the whole element from that buffer on every call:

Transcrypt/transcrypt/modules/org/transcrypt/__runtime__.py

Lines 284 to 288 in 32b216b

	def print (self, *args, sep = ' ', end = '\n'):
	self.buffer = '{}{}{}'.format (self.buffer, sep.join ([str (arg) for arg in args]), end) [-4096 : ]
	if self.element:
	self.element.innerHTML = self.buffer.replace ('\n', '<br>') .replace (' ', '&nbsp')

The class offers no method to reset self.buffer. Replacing the module-level instance does not help either, because print and input are bound to the original instance when the runtime module is loaded:

Transcrypt/transcrypt/modules/org/transcrypt/__runtime__.py

Lines 301 to 304 in 32b216b

	__terminal__ = __Terminal__ ()
	print = __terminal__.print
	input = __terminal__.input

Proposed fix

Add a clear() method that resets buffer and element together, so the buffer cannot restore stale output:

    def clear (self):
        self.buffer = ''

        if self.element:
            self.element.innerHTML = '_'

'_' is the initial content written by __init__, so clear() returns the terminal to its start state.

Workaround

Reset both parts by hand:

__terminal__.buffer = ''
__terminal__.element.innerHTML = ''

Version

Transcrypt 3.9.5

Contribution

I am happy to write the pull request for this change if the proposed approach is acceptable.