[PyQt] from PyQt5.Qt import *

[Christian Tismer]

On 28.06.18 13:27, Kyle Altendorf wrote:
> On 2018-06-28 01:25, Zhao Lee wrote:
>> but now I could replace all of them with only " from PyQt5.Qt import * "
> 
>> any drawback along with the single line import ?
> 
> The doc you linked explained the memory cost of importing anything via
> the PyQt5.Qt module.  There are additional reasons that from imports are
> somewhat risky and * imports are generally fairly questionable.
> 
> When you `from x import y` you are making a new name (`y`) referencing
> the object referenced by `x.y` at that point in time.  Generally, module
> globals (such as `y` in this example) should not be reassigned but it
> can and does happen.  Then when you use `y` you will still get the old
> object, not the new.
> 
> https://repl.it/@altendky/why-not-to-from-import
> 
> `from x import *` has the same issue, but additionally people reading
> the code don't know where names came from.  With a single `import *`
> it's annoying, with two...  we end up having to add diagnostics to the
> code and run it ourselves to figure out where the otherwise unknown
> variables came from.  Dumping things into the module scope with this
> hazards some confusing behavior with some packages like numpy that have
> lots of things with fairly 'normal' names in them.  You end up with
> collisions and some names being unexpectedly overwritten possibly
> depending on the order of imports.
> 
> Admittedly, Qt suffers from mostly the opposite namespacing issue in
> that you end up triple namespaced because each layer of
> PyQt5.QtWidgets.QApplication has the indicative Q in it.  Still, these
> problems are generally relevant to `from` and `*` imports.


You are generally very right concerning "from xxx import *".
People should avoid that feature, at least in all scripts.

There is just a single exception that I built explicitly
into our new PySide2 version:

It allows to write "from PySide2 import *".
This is very handy and very clean, because everybody knows
that you will get all the QtXXX modules which are available.

Cheers -- Chris

-- 
Christian Tismer-Sperling    :^)   tismer at stackless.com
Software Consulting          :     http://www.stackless.com/
Karl-Liebknecht-Str. 121     :     http://pyside.org
14482 Potsdam                :     GPG key -> 0xE7301150FB7BEE0E
phone +49 173 24 18 776  fax +49 (30) 700143-0023

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 496 bytes
Desc: OpenPGP digital signature
URL: <https://www.riverbankcomputing.com/pipermail/pyqt/attachments/20180628/978cc192/attachment.sig>