QGIS » QGIS Application

import os

import sys

import glob

import traceback

from PyQt4.QtCore import QCoreApplication

from qgis.core import QgsApplication, QgsMessageLog

def load_user_expressions(path):

    """

    Load all user expressions from the given paths

    """

    #Loop all py files and import them

    modules = glob.glob(path + "/*.py")

    names = [os.path.basename(f)[:-3] for f in modules]

    for name in names:

        if name == "__init__":

            continue

        # As user expression functions should be registered with qgsfunction

        # just importing the file is enough to get it to load the functions into QGIS

        try:

            __import__("expressions.{0}".format(name), locals(), globals())

        except:

            error = traceback.format_exc()

            msgtitle = QCoreApplication.translate("UserExpressions", "User expressions")

            msg = QCoreApplication.translate("UserExpressions", "The user expression {0} is not valid").format(name)

            QgsMessageLog.logMessage(msg +"\n"+ error, msgtitle, QgsMessageLog.WARNING)

userpythonhome = os.path.join(QgsApplication.qgisSettingsDirPath(), "python")

expressionspath = os.path.join(userpythonhome, "expressions")

startuppy = os.path.join(userpythonhome, "startup.py")

sys.path.append(userpythonhome)

# exec startup script

if os.path.exists(startuppy):

    execfile(startuppy, locals(), globals())

if not os.path.exists(expressionspath):

    os.makedirs(expressionspath)

initfile = os.path.join(expressionspath, "__init__.py")

if not os.path.exists(initfile):

    open(initfile, "w").close()

try:

    import expressions

    expressions.load = load_user_expressions

    expressions.load(expressionspath)

    expressions.template = """\"\"\"

Define new functions using @qgsfunction. feature and parent must always be the

last args. Use args=-1 to pass a list of values as arguments

\"\"\"

from qgis.core import *

from qgis.gui import *

@qgsfunction(args='auto', group='Custom')

def func(value1, feature, parent):

    return value1

"""

except ImportError:

    # We get a import error and crash for some reason even if we make the expressions package

    # TODO Fix the crash on first load with no expressions folder

    # But for now it's not the end of the world if it doesn't laod the first time

    pass