Intro

This project provides two fixer plugins for the lib2to3 module:

1. signals to migrate old style Qt signals to new-style ones.
2. args to migrate QString.arg calls in Python string.format.

Signals

Warning: this is an ugly hack. Mostly for use in converting the taurus project signals (see https://sf.net/p/tauruslib/tickets/187/). The fixer can be invoked with the provided 'my2to3' script.

my2to3 -f signals can be used as a first step, but manual tweaking is necessaryin the fixer code.

It is based on code from qgis

When run, it does its best in automating the migration and leaves a SIGNALS_TODO.log file with notes of identified things that need manual tweaking.

Usage

my2to3 -f signals [options] <dir_or_file_to_fix>

Usemy2to3 -h for info on available options inherited from 2to3

For example:

my2to3 -f signals -w example-signals.py

When converting a full package instead of a small file, I recommend to redirect the output to a file for future reference. e.g.:

my2to3 -f signals -w ~/src/taurus/lib > signalschange.log

Example

Now let's see an example. Consider the following code from the example-signals.py:

from PyQt4 import Qt

MY_SIGNATURE = 'some_signal_name'
MY_SIG = Qt.SIGNAL('some_other_signal_name')

class MyWidget(Qt.QWidget):

    def m1(self):
        self.connect(self, Qt.SIGNAL('mysigname'), self.myslot)
        self.emit(Qt.SIGNAL('mysigname'), 1, 2)

    def m2(self):
        self.connect(self, Qt.SIGNAL(MY_SIGNATURE), self.myslot)
        self.emit(Qt.SIGNAL(MY_SIGNATURE), 3, 4)

    def m3(self):
        self.connect(self, MY_SIG, self.myslot)
        self.emit(MY_SIG, 5, 6)

    def myslot(self, a, b):
        print a, b, a + b

If we run the script with:

my2to3 -f signals -nwo outdir example-signals.py

We get the following transformed outdir/example-signals.py file :

from PyQt4 import Qt

MY_SIGNATURE = 'some_signal_name'
MY_SIG = Qt.SIGNAL('some_other_signal_name')

class MyWidget(Qt.QWidget):

    def m1(self):
        self.mysigname.connect(self.myslot)
        self.mysigname.emit(1, 2)

    def m2(self):
        self.connect(self, Qt.SIGNAL(MY_SIGNATURE), self.myslot)
        self.emit(Qt.SIGNAL(MY_SIGNATURE), 3, 4)

    def m3(self):
        self.connect(self, MY_SIG, self.myslot)
        self.emit(MY_SIG, 5, 6)

    def myslot(self, a, b):
        print a, b, a + b

Now, note that there are several things that still need manual fixing:

• The mysigname signal needs to be declared. We need to add a class member like

  mysigname = Qt.pyqtSignal(int, int)
  

  Note that the types need to be inferred from studying the code if the signal signature does not include them. Looking at the emit parameters and the slot code may help.

• The emit and connects from methods m2 and m3 are not transformed at all. This is because there is no safe way to deal with the possible indirections in all cases. Just transform them manually.

These pending things are logged in a file called 'SIGNALS_TODO.log'. In this case, the log looks as follows:

NEEDS_DECLARE:
  MyWidget:         self.mysigname

NOT_CONVERTED:
 self.connect(self, Qt.SIGNAL(MY_SIGNATURE), self.myslot)

NOT_CONVERTED:
         self.emit(Qt.SIGNAL(MY_SIGNATURE), 3, 4)

NOT_CONVERTED:
 self.connect(self, MY_SIG, self.myslot)

NOT_CONVERTED:
         self.emit(MY_SIG, 5, 6)

Finally, note that the stdout has interesting info

$ ./my2to3 -f signals -nwo outdir example-signals.py
lib2to3.main: Output in 'outdir' will mirror the input directory '' layout.
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt

SKIPPING non trivial signal:
self.connect(self, Qt.SIGNAL(MY_SIGNATURE), self.myslot)


SKIPPING non trivial signal:
        self.emit(Qt.SIGNAL(MY_SIGNATURE), 3, 4)


SKIPPING non trivial signal:
self.connect(self, MY_SIG, self.myslot)


SKIPPING non trivial signal:
        self.emit(MY_SIG, 5, 6)

RefactoringTool: Refactored example-signals.py
--- example-signals.py  (original)
+++ example-signals.py  (refactored)
@@ -6,8 +6,8 @@
 class MyWidget(Qt.QWidget):
 
     def m1(self):
-        self.connect(self, Qt.SIGNAL('mysigname'), self.myslot)
-        self.emit(Qt.SIGNAL('mysigname'), 1, 2)
+        self.mysigname.connect(self.myslot)
+        self.mysigname.emit(1, 2)
 
     def m2(self):
         self.connect(self, Qt.SIGNAL(MY_SIGNATURE), self.myslot)
RefactoringTool: Writing converted example-signals.py to outdir/example-signals.py.
RefactoringTool: Files that were modified:
RefactoringTool: example-signals.py

Note of caution for overloaded signals

Currently, the signals fixer ignores the types in the signal signatures. This may be problematic in some cases for overloaded signals connected to overloaded slots: while PyQt will usually select the appropriate overload depending on the slot to which the signal is connected, this may not work as expected if the slot itself has optional parameters (i.e. if it is also "overloaded"). In those cases, an explicit selection of the right type should be manually done in the emit call.

TODO: I haven't bothered to look, but it seems that this could be automated by making the fixer explicit the type when translating emit calls.

Args

Usage

my2to3 -f args [options] <dir_or_file_to_fix>

For example:

my2to3 -f args -w example-args.py

Outputs:

root: Generating grammar tables from /usr/lib/python3.5/lib2to3/PatternGrammar.txt
RefactoringTool: Refactored example-args.py
--- example-args.py	(original)
+++ example-args.py	(refactored)
@@ -2,6 +2,6 @@
 
 class Window(QLabel):
     def foo(self, value, tr=None):
-        self.tr("Messaggio %1").arg(self.getText())  # cose
-        tr("Messaggio %1 e %2").arg(self.getText()).arg(value)
-        qApp.translate("Messaggio %1 e %2").arg(self.getText(), value)
+        self.tr("Messaggio {0}").format(self.getText())  # cose
+        tr("Messaggio {0} e {1}").format(self.getText(), value)
+        qApp.translate("Messaggio {0} e {1}").format(self.getText(), value)
RefactoringTool: Files that need to be modified:
RefactoringTool: example-args.py

Interesting references

1. Understanding custom lib2to3 fixers: http://python3porting.com/fixers.html
2. New style signals: http://pyqt.sourceforge.net/Docs/PyQt4/new_style_signals_slots.html