Performance hit on import Qt

[fredrikaverpil]

Importing the .Qt submodule of PyQt means "import all" which might give a performance hit, when one might only end up using QtWidgets (?)

Not sure what you meant here @mottosso

[mottosso]

PyQt has this convenience feature that when you import PyQt5.Qt it will import all classes under the same namespace. So even if you aren't using QtQml, it would still get imported, which I am just assuming adds to the amount of time it takes to import.

I'm sure there is reference of it in the documentation, but couldn't find it just now. This was the closest thing I found.

• https://stackoverflow.com/questions/21323899/import-pyqt4-does-not-include-pyqt4-qtcore-or-qtgui

To solve this, I would rather find a way of only importing what the user actually imports.

from Qt import QtWidgets
# Should not import QtCore, QtQuick.. etc.

Alternatively if we test and make sure it actually does take longer, maybe it doesn't, in which case there's nothing to worry about.

[pipoun]

With current Qt.py implementation, in function _pyqt4() if you replace

import PyQt4.Qt

with

import PyQt4.QtCore
import PyQt4.QtGui

to avoid importing PyQt4.Qt (and the performance hit), the following code doesn't work any more.

>>> import Qt
>>> import Qt.QtSvg
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: dynamic module not initialized properly

[mottosso]

Yes, importing it all at once has been the only way I haven't run into problems. Me thinks there is some magic happening on import of the PyQt modules.

[fredrikaverpil]

This thread is interesting and somewhat related to this issue: https://www.riverbankcomputing.com/pipermail/pyqt/2016-September/038019.html

"from foo import bar" is equivalent to:

   import foo
   bar = foo.bar
   del foo

[mottosso]

This isn't solvable anymore, since 1.0, as we are explicitly importing every single member in order to map it correctly. Nor may it ever have needed a solution.