Compiling UI and resource files with PyQt

#python #qt #pyqt

This article was originally published years ago at https://mplicka.cz/en/blog/compiling-ui-and-resource-files-with-pyqt and it's about Qt4/PyQt4. Since it still has some hits coming from Google search, some people may find it useful.

PyQt is a python binding for popular Qt library (which became LGPLed for non-commercial purposes recently). If you use Qt Designer, you have to compile XML description of UI or Qt resource files to Python code to use them in your application.

In C++, you can easily use qmake tool or Automake for creating suitable Makefile. For Python, there is no Makefile needed since Python compiles modules as they are loaded into VM. With PyQt, you can use uic module for compiling ui files or loading them as a Python class.

Alternatively, you can use pyuic4 and pyrcc4 command line tools in the similar way as appropriate Qt tools (uic, rcc). I'm using this way to produce Python code. Both tools have similar usage:

#compile ui file from Qt Designer
pyuic4 ui_file.ui -o compiled_ui_file.py
#compile resource file (icons, etc..)
pyrcc4 resource_file.qrc -o compiled_resource_file.py

Formerly, I had one shell script to compile all my resource files in project at once (because I was too lazy). This solution has two main disadvantages. At first, compilation of all resources takes more time than compiling of modified files only. This varies with amount of resource files your project has. The second one is more annoying to me. Since I also track compiled versions of UI and resource files (for no particular reason yet) with Mercurial, it always creates new changeset because ''pyuic4'' tool adds information about compile time to Python code comments. So I refreshed my Makefile knowledge (and also used some old code snippets) and created following Makefile for compiling UI and resource files separately.

###### EDIT ##################### 
#Directory with ui and resource files
RESOURCE_DIR = src/resources

#Directory for compiled resources
COMPILED_DIR = src/ui

#UI files to compile
UI_FILES = confirm.ui main.ui repair.ui settings.ui statistics.ui
#Qt resource files to compile
RESOURCES = images.qrc 

#pyuic4 and pyrcc4 binaries
PYUIC = pyuic4.bat
PYRCC = pyrcc4

#################################
# DO NOT EDIT FOLLOWING

COMPILED_UI = $(UI_FILES:%.ui=$(COMPILED_DIR)/ui_%.py)
COMPILED_RESOURCES = $(RESOURCES:%.qrc=$(COMPILED_DIR)/%_rc.py)

all : resources ui 

resources : $(COMPILED_RESOURCES) 

ui : $(COMPILED_UI)

$(COMPILED_DIR)/ui_%.py : $(RESOURCE_DIR)/%.ui
    $(PYUIC) $< -o $@

$(COMPILED_DIR)/%_rc.py : $(RESOURCE_DIR)/%.qrc
    $(PYRCC) $< -o $@

clean : 
    $(RM) $(COMPILED_UI) $(COMPILED_RESOURCES) $(COMPILED_UI:.py=.pyc) $(COMPILED_RESOURCES:.py=.pyc)

It works with GNU Make (from Cygwin or MigGW on Windows). It compiles files in following manner:

window.ui --> ui_window.py (GUI definition)
images.qrc --> images_rc.py (resources)

Now you can easily compile only modified files by only typing make in console. Make sure that your current working directory contains Makefile shown above.