PEP 0526 -- variable declarations (#70)

This PEP is *not* ready for review! This commit is just to claim the PEP number.

pep-0526.txt

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+PEP: 526
+Title: Variable Declaration Syntax
+Version: $Revision$
+Last-Modified: $Date$
+Author: Ryan Gonzalez <rymg19@gmail.com>, Philip House <phouse512@gmail.com>, Guido van Rossum <guido@python.org>
+Status: Draft
+Type: Standards Track
+Content-Type: text/x-rst
+Created: 09-Aug-2016
+Python-Version: 3.6
+
+Abstract
+========
+
+PEP 484 introduced type hints and; In particular, it introduced the notion of
+type comments::
+
+  # a is specified to be a list of ints.
+  a = []  # type: List[int]
+  # b is a string
+  b = None  # type: str
+  class Cls:
+    my_class_attr = True  # type: bool
+
+This PEP aims at adding syntax to Python for declaring the types of variables and
+attributes, instead of expressing them through comments::
+
+  a: List[int] = []
+  b: str
+  class Cls:
+    my_class_attr: ClassAttr[bool] = True
+
+Rationale
+=========
+
+Although type comments work well, the fact that they're expressed through
+comments has some downsides:
+
+- Text editors often highlight comments differently from type declarations.
+- There isn't a way to declare the type of an undefined variable; you need to
+  initialize it to ``None`` (e.g. ``a = None # type: int``).
+- Variables declared in a conditional branch are difficult to read::
+
+    if some_value:
+        my_var = function() # type: Logger
+    else:
+        my_var = another_function() # Why isn't there a type here?
+
+- Since type comments aren't actually part of the language, if a Python script
+  wants to parse them, it would require a custom parser instead of just using
+  ``ast``.
+- It's impossible to retrieve the annotations at runtime outside of attempting to
+  find the module's source code and parse it at runtime, which is inelegant, to
+  say the least.
+
+The majority of these issues can be alleviated by making the syntax a core part of
+the language.