Updating to API version 3.0 (Python 3).md

Updating to API version 3.0+ (Python 3) - random things we've run across and definitely not exhaustive

• imports implicit imports are no longer honored in the way they were in Python 2. Python PEP 328 explains the issues with implicit (relative) imports. See also Package Relative Imports

  # Python 2:
  import foo
  # Python 3:
  from .foo import *
  from .foo import (bar, baz)

• print statement change - in python 3 it requires that the string be enclosed in parens:

  # Python 2:
  print "some string here"
  # Python 2 & 3:
  print("some string here")

• Exception declarations

  # Python 2:
  except ExceptionHere, exc:
  # Python 2 & 3:
  except ExceptionHere as exc:

• The StandardError exception is deprecated, so replace with Exception

• JSON

  # In API versions < 3.0, this works:
  import simplejson
  import simplejson as json
  # In API versions >= 3.0:
  import json

• unicode is no longer a type, so this fails:

  isinstance(some_var, unicode)

  since all strings are by default unicode

• replace file() with open()

• if opening a utf-8 file, open("file.json", encoding="utf-8")

• indigo.kStateImageSel.None is now a syntax error because None is a keyword. You must change those occurrances to indigo.kStateImageSel.NoImage in Python 3. Also, you can use the following in place of the indigo specifier directly and it should work correctly in either version:

  getattr(indigo.kStateImageSel, "NoImage", getattr(indigo.kStateImageSel, "None", ""))

  which could also be written as a function:

  def _no_image():
      try:
          return getattr(indigo.kStateImageSel, "NoImage")
      except:
          return getattr(indigo.kStateImageSel, "None")

• socket.error is aliased to OSError (and it's deprecated anyway), though socket.timeout remains. There is now a top-level exception called ConnectionResetError which may be what you were looking for: also ConnectionRefusedError. Just don't get fooled if you try to subscript what you think is a socket.error only to get a message about OSError not being subscriptable...

• socket communication now uses the bytes data type rather than str (because str is now unicode). If your plugin uses socket communications, you are going to need to make sure that you encode/decode appropriately in the code that surrounds your socket communication. If you have a string (like json for instance), then you'll need to encode that str into bytes. Likewise, when you receive something from a socket you'll need to decode those bytes into a str. Simple example:

  >>> s = "Testing special characters like é, ç, etc"
  >>> b = s.encode("utf8")
  >>> b
  b'Testing special characters like \xc3\xa9, \xc3\xa7, etc'
  >>> b.decode("utf8")
  'Testing special characters like é, ç, etc'

  Don't forget to convert when using for logging messages where you insert them using the format() command or you'll end up seeing some strangeness:

  >>> "bytes: {}".format(b)
  "bytes: b'Testing special characters like \\xc3\\xa9, \\xc3\\xa7, etc'"
  >>> "str: {}".format(b.decode("utf8"))
  'str: Testing special characters like é, ç, etc'

• Division results on integers can result in a float:

  >>> # python 2
  ... 2/3
  0
  >>> # python 3
  >>> 2/3
  0.6666666666666666

  but you can get old results by using double slashes:

  >>> # python 3
  >>> 2//3
  0

  which, btw, also works in python 2.7

• Many dict iterators (items(), keys(), values()) now return "view" objects. In general this isn't an issue, but if you are deleting stuff while iterating through one of those views, you'll get a RuntimeError:

  d = {"a": 1, "b": 2, "c": 3}
  for k in d.keys():
      del d[k]
      
  Traceback (most recent call last):
    File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/code.py", line 90, in runcode
      exec(code, self.locals)
    File "<input>", line 1, in <module>
  RuntimeError: dictionary changed size during iteration

  so you'll first want to make a copy to iterate over:

  for k in d.copy().keys():
      del d[k]

• dict.iteritems() is deprecated, dict.items() works just as well in both python 2 & 3 (same for all the iter* functions on dict and list objects).

• pylint -py3k may give you this error: round built-in referenced (round-builtin). This warning can safely be ignored since it's primarily just a reminder that the algorithm for calculating how an exact halfway cases has changed in python 3.