Changed transpose property to function.

[tdiethe]

This stops the debugger accidentally creating new variables on access.

Description of changes:
When using an interactive debugger (e.g. PyCharm), inspecting any Variable object invokes the property T which has the side effect of creating new variables that are not part of the graph. By changing this to a function .transpose() the functionality is maintained (at the slight expense of ease of use) whilst preventing this from happening.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #137 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop     #137   +/-   ##
========================================
  Coverage    85.11%   85.11%           
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  Files           77       77           
  Lines         3817     3817           
  Branches       653      653           
========================================
  Hits          3249     3249           
  Misses         375      375           
  Partials       193      193

Impacted Files	Coverage Δ
mxfusion/components/variables/variable.py	87.16% <100%> (ø)	⬆️

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[zhenwendai]

inspecting any Variable object invokes the property T which has the side effect of creating new variables that are not part of the graph.

Could you give an example? I think the resulting variable should be in the graph but without an explicit reference.

One way to provide the property T is to cache the outcome variable (as the transpose of a variable should always be the same).

I don't think we should make this change, instead should just remove the transpose property altogether.

[meissnereric]

I think you're right that a property like this shouldn't have side effects. But if it's not a property, I would rather remove the transpose function altogether from the Variable class, and ask users to just call the transpose operator.

[tdiethe]

Conclusion on this? Do you want me to update the PR to remove the function entirely?

[meissnereric]

That is my preference yeah Tom. Don't remove the operator, just the member method in Variable.