J5’s Blog

The hackfest is over and a lot of things got fixed but unfortunately Python3 support was broken.  I just committed a couple of patches to fix this.  Here are some things PyGObject developers should look out for. When I note to only use something in tests it means that there is a compat module that is only available to the tests. Actual code should either add the workaround to the top of their module or try not to have a distinction between things such as unicode and longs which no longer exist in Python 3.

• use range instead of xrange – loss of performance in Python 2 but Python 3 treats range similarly to python 2’s xrange
• use dict.items() instead of dict.iteritems() – same as the xrange issue
• callable does not exist in 3.x, use hasattr(obj, ‘__call__’) or

            if sys.version_info > (3, 0):
                def callable(obj):
                    return hasattr(obj, '__call__')
      

• using unicode in tests is tricky, you can’t use u” even in a versioned conditional as python3’s parser chokes on it. Do this in tests (and only i
  in tests):

            from compathelper import _unicode
            unicode_string = _unicode('this is a unicode string')
      

• exception caching changed in 2.7, instead of except Exception, e we now use except Exception as e. Do this to be compatible with older versions:

            except Exception:
                etype, e = sys.exc_info()[:2]
      

• Unbound methods with an im_func attribute no longer exits in 3.x. Unbound methods are now just functions so class.method in 3.x is equivalent to class.method.im_func in 2.x. If you have to go this low level do this:

            func = class.method
            if sys.version_info < (3,0):
                func = func.im_func
      

  Update: It was pointed out to me that this can be expressed as a simple getattr triple:

            getattr(class.method, 'im_func', class.method)
      

• all numbers are long in 3.x so 42L is invalid in 3.x. In tests (and only in tests) do this:

            from compathelper import _long
            l = _long(42)
      

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