My QGIS plugin shows GUI but not Works. How to get Error log?

Question

I am new to PyQgis. I made a simple calculator with PyQt4, now I am trying to run it under QGIS. I connected calculator as plugin, and tested it, its GUI works without error but it does not calculates anything.

How can I get error log?

calculator.py:

# -*- coding: utf-8 -*-

from PyQt4 import QtCore, QtGui
from calculate_ui import Ui_Dialog
from math import *
from qgis.core import *

def derece(degrees):
    return degrees*((2*pi)/400)

class Dialog(QtGui.QDialog, Ui_Dialog):
    def __init__(self, iface):
      QtGui.QDialog.__init__(self)
      self.iface = iface
      self.setupUi(self)
      self.ui = Ui_Dialog()
      self.ui.setupUi(self)
      # Validations
      tempValidator = QtGui.QDoubleValidator()
      tempValidator.setNotation(QtGui.QDoubleValidator.StandardNotation)
      self.ui.at.setValidator(tempValidator)
      self.ui.Rt.setValidator(tempValidator)
      # Signal/slot connections.
      self.setupConnections()

    def calc(self):
      a = float(self.ui.at.text())
      R = float(self.ui.Rt.text())

      T=R*tan(derece(a/2))
      L=(2*pi*R*a)/400
      BS=(R/cos(derece(a/2)))-R

      self.ui.Tt.setText(str(T))
      self.ui.Lt.setText(str(L))
      self.ui.BSt.setText(str(BS))
    def silk(self):
      self.ui.at.clear()
      self.ui.Rt.clear()
      self.ui.Tt.clear()
      self.ui.Lt.clear()
      self.ui.BSt.clear()

    def setupConnections(self):

      self.connect(self.ui.hesaplak, QtCore.SIGNAL('clicked()'),
          self.calc)
      self.connect(self.ui.temizlek, QtCore.SIGNAL('clicked()'),
          self.silk)

You can take a look at the plugin from here.

Answer 1

Python messages can be printed to the python console.

This is accessed from Plugins> Python Console.

Answer 2

Probably your connections are wrong.

Remove your setupConnections function, and connect them under __init__:

self.ui.hesaplak.clicked.connect(self.calc)
self.ui.temizlek.clicked.connect(self.silk)

I guess your derece function also should be inside the class (then call it with self.).