This recipe adds parameter type checking to each method or function invocation. Not a replacement for static typing, but it makes a nice pair of shackles to me.
Python, 430 lines
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# -*- coding: iso-8859-1 -*-
################################################################################
#
# Method call parameters/return value type checking decorators.
# (c) 2006-2007, Dmitry Dvoinikov <dmitry@targeted.org>
# Distributed under BSD license.
#
# Samples:
#
# from typecheck import *
#
# @takes(int, str) # takes int, str, upon a problem throws InputParameterError
# @returns(int) # returns int, upon a problem throws ReturnValueError
# def foo(i, s):
# return i + len(s)
#
# @takes((int, long), by_regex("^[0-9]+$")) # int or long, numerical string
# def foo(i, s, anything): # and the third parameter is not checked
# ...
#
# @takes(int, int, foo = int, bar = optional(int)) # keyword argument foo must be int
# def foo(a, b, **kwargs): # bar may be int or missing
# ...
#
# Note: @takes for positional arguments, @takes for keyword arguments and @returns
# all support the same checker syntax, for example for the following declaration
#
# @takes(C)
# def foo(x):
# ...
#
# then C may be one of the simple checkers:
#
# --------- C --------- ------------- semantics -------------
# typename ==> ok if x is is an instance of typename
# "typename" ==> ok if x is is an instance of typename
# with_attr("a", "b") ==> ok if x has specific attributes
# some_callable ==> ok if some_callable(x) is True
# one_of(1, "2") ==> ok if x is one of the literal values
# by_regex("^foo$") ==> ok if x is a matching basestring
# nothing ==> ok if x is None
# anything ==> always ok
#
# simple checkers can further be combined with OR semantics using tuples:
#
# --------- C --------- ------------- semantics -------------
# (checker1, checker2) ==> ok if x conforms with either checker
#
# be optional:
#
# --------- C --------- ------------- semantics -------------
# optional(checker) ==> ok if x is checker-conformant or None
#
# or nested recursively into one of the following checkers
#
# --------- C --------- ------------- semantics -------------
# list_of(checker) ==> ok if x is a list of checker-conformant values
# tuple_of(checker) ==> ok if x is a tuple of checker-conformant values
# set_of(checker) ==> ok if x is a set of checker-conformant values
# dict_of(key_checker, value_checker) ==> ok if x is a dict mapping key_checker-
# conformant keys to value_checker-conformant values
#
# More samples:
#
# class foo(object):
# @takes("foo", optional(int)) # foo, maybe int, but foo is yet incomplete
# def __init__(self, i = None): # and is thus specified by name
# ...
# @takes("foo", int) # foo, and int if presents in args,
# def bar(self, *args): # if args is empty, the check passes ok
# ...
# @takes("foo")
# @returns(object) # returns foo which is fine, because
# def biz(self): # foo is an object
# return self
# @classmethod # classmethod's and staticmethod's
# @takes(type) # go same way
# def baz(cls):
# ...
#
# @takes(int)
# @returns(optional("int", foo)) # returns either int, foo or NoneType
# def bar(i): # "int" (rather than just int) is for fun
# if i > 0:
# return i
# elif i == 0:
# return foo() # otherwise returns NoneType
#
# @takes(callable) # built-in functions are treated as predicates
# @returns(lambda x: x == 123) # and so do user-defined functions or lambdas
# def execute(f, *args, **kwargs):
# return f(*args, **kwargs)
#
# assert execute(execute, execute, execute, lambda x: x, 123) == 123
#
# def readable(x): # user-defined type-checking predicate
# return hasattr(x, "read")
#
# anything is an alias for predicate lambda: True,
# nothing is an alias for NoneType, as in:
#
# @takes(callable, readable, optional(anything), optional(int))
# @returns(nothing)
# def foo(f, r, x = None, i = None):
# ...
#
# @takes(with_attr("read", "write")) # another way of protocol checking
# def foo(pipe):
# ...
#
# @takes(list_of(int)) # list of ints
# def foo(x):
# print x[0]
#
# @takes(tuple_of(callable)) # tuple of callables
# def foo(x):
# print x[0]()
#
# @takes(dict_of(str, list_of(int))) # dict mapping strs to lists of int
# def foo(x):
# print sum(x["foo"])
#
# @takes(by_regex("^[0-9]{1,8}$")) # integer-as-a-string regex
# def foo(x):
# i = int(x)
#
# @takes(one_of(1, 2)) # must be equal to either one
# def set_version(version):
# ...
#
# The (3 times longer) source code with self-tests is available from:
# http://www.targeted.org/python/recipes/typecheck.py
#
################################################################################
__all__ = [ "takes", "InputParameterError", "returns", "ReturnValueError",
"optional", "nothing", "anything", "list_of", "tuple_of", "dict_of",
"by_regex", "with_attr", "one_of", "set_of" ]
no_check = False # set this to True to turn all checks off
################################################################################
from inspect import getargspec, isfunction, isbuiltin, isclass
from types import NoneType
from re import compile as regex
################################################################################
def base_names(C):
"Returns list of base class names for a given class"
return [ x.__name__ for x in C.__mro__ ]
################################################################################
def type_name(v):
"Returns the name of the passed value's type"
return type(v).__name__
################################################################################
class Checker(object):
def __init__(self, reference):
self.reference = reference
def check(self, value): # abstract
pass
_registered = [] # a list of registered descendant class factories
@staticmethod
def create(value): # static factory method
for f, t in Checker._registered:
if f(value):
return t(value)
else:
return None
################################################################################
class TypeChecker(Checker):
def check(self, value):
return isinstance(value, self.reference)
Checker._registered.append((isclass, TypeChecker))
nothing = NoneType
################################################################################
class StrChecker(Checker):
def check(self, value):
value_base_names = base_names(type(value))
return self.reference in value_base_names or "instance" in value_base_names
Checker._registered.append((lambda x: isinstance(x, str), StrChecker))
################################################################################
class TupleChecker(Checker):
def __init__(self, reference):
self.reference = map(Checker.create, reference)
def check(self, value):
return reduce(lambda r, c: r or c.check(value), self.reference, False)
Checker._registered.append((lambda x: isinstance(x, tuple) and not
filter(lambda y: Checker.create(y) is None,
x),
TupleChecker))
optional = lambda *args: args + (NoneType, )
################################################################################
class CallableChecker(Checker):
def check(self, value):
return self.reference(value)
# note that the callable check is the most relaxed of all, therefore it should
# be registered last, after all the more specific cases have been registered
Checker._registered.append((callable, CallableChecker))
anything = lambda *args: True
################################################################################
class ListOfChecker(Checker):
def __init__(self, reference):
self.reference = Checker.create(reference)
def check(self, value):
return isinstance(value, list) and \
not filter(lambda e: not self.reference.check(e), value)
list_of = lambda *args: ListOfChecker(*args).check
################################################################################
class TupleOfChecker(Checker):
def __init__(self, reference):
self.reference = Checker.create(reference)
def check(self, value):
return isinstance(value, tuple) and \
not filter(lambda e: not self.reference.check(e), value)
tuple_of = lambda *args: TupleOfChecker(*args).check
################################################################################
class SetOfChecker(Checker):
def __init__(self, reference):
self.reference = Checker.create(reference)
def check(self, value):
return isinstance(value, set) and \
not filter(lambda e: not self.reference.check(e), value)
set_of = lambda *args: SetOfChecker(*args).check
################################################################################
class DictOfChecker(Checker):
def __init__(self, key_reference, value_reference):
self.key_reference = Checker.create(key_reference)
self.value_reference = Checker.create(value_reference)
def check(self, value):
return isinstance(value, dict) and \
not filter(lambda e: not self.key_reference.check(e), value.iterkeys()) and \
not filter(lambda e: not self.value_reference.check(e), value.itervalues())
dict_of = lambda *args: DictOfChecker(*args).check
################################################################################
class RegexChecker(Checker):
def __init__(self, reference):
self.reference = regex(reference)
def check(self, value):
return isinstance(value, basestring) and self.reference.match(value)
by_regex = lambda *args: RegexChecker(*args).check
################################################################################
class AttrChecker(Checker):
def __init__(self, *attrs):
self.attrs = attrs
def check(self, value):
return reduce(lambda r, c: r and c, map(lambda a: hasattr(value, a), self.attrs), True)
with_attr = lambda *args: AttrChecker(*args).check
################################################################################
class OneOfChecker(Checker):
def __init__(self, *values):
self.values = values
def check(self, value):
return value in self.values
one_of = lambda *args: OneOfChecker(*args).check
################################################################################
def takes(*args, **kwargs):
"Method signature checking decorator"
# convert decorator arguments into a list of checkers
checkers = []
for i, arg in enumerate(args):
checker = Checker.create(arg)
if checker is None:
raise TypeError("@takes decorator got parameter %d of unsupported "
"type %s" % (i + 1, type_name(arg)))
checkers.append(checker)
kwcheckers = {}
for kwname, kwarg in kwargs.iteritems():
checker = Checker.create(kwarg)
if checker is None:
raise TypeError("@takes decorator got parameter %s of unsupported "
"type %s" % (kwname, type_name(kwarg)))
kwcheckers[kwname] = checker
if no_check: # no type checking is performed, return decorated method itself
def takes_proxy(method):
return method
else:
def takes_proxy(method):
method_args, method_defaults = getargspec(method)[0::3]
def takes_invocation_proxy(*args, **kwargs):
# append the default parameters
if method_defaults is not None and len(method_defaults) > 0 \
and len(method_args) - len(method_defaults) <= len(args) < len(method_args):
args += method_defaults[len(args) - len(method_args):]
# check the types of the actual call parameters
for i, (arg, checker) in enumerate(zip(args, checkers)):
if not checker.check(arg):
raise InputParameterError("%s() got invalid parameter "
"%d of type %s" %
(method.__name__, i + 1,
type_name(arg)))
for kwname, checker in kwcheckers.iteritems():
if not checker.check(kwargs.get(kwname, None)):
raise InputParameterError("%s() got invalid parameter "
"%s of type %s" %
(method.__name__, kwname,
type_name(kwargs.get(kwname, None))))
return method(*args, **kwargs)
takes_invocation_proxy.__name__ = method.__name__
return takes_invocation_proxy
return takes_proxy
class InputParameterError(TypeError): pass
################################################################################
def returns(sometype):
"Return type checking decorator"
# convert decorator argument into a checker
checker = Checker.create(sometype)
if checker is None:
raise TypeError("@returns decorator got parameter of unsupported "
"type %s" % type_name(sometype))
if no_check: # no type checking is performed, return decorated method itself
def returns_proxy(method):
return method
else:
def returns_proxy(method):
def returns_invocation_proxy(*args, **kwargs):
result = method(*args, **kwargs)
if not checker.check(result):
raise ReturnValueError("%s() has returned an invalid "
"value of type %s" %
(method.__name__, type_name(result)))
return result
returns_invocation_proxy.__name__ = method.__name__
return returns_invocation_proxy
return returns_proxy
class ReturnValueError(TypeError): pass
################################################################################
# EOF
|
What I would initially wanted such decorators to look like was: <pre> class foo: @takes(foo, int) def bar(self, i): return i </pre> so that foo().bar("happy") throws, or <pre> class foo: @returns(int) def bar(self, i): return i </pre> and foo().bar("pity") throws again (for different reason).
There appears to be a problem though - declaration such as <pre> class foo: @takes(foo) # foo is not known at this point def bar(self): ... </pre> is impossible, because foo is incomplete by the time the decorator picks it up.
I came up with the following workaround (arguably rather standard): <pre> class foo: @takes("foo") # "foo" is a name of a class, not a class itself def bar(self): ... </pre>
Keyword arguments can be checked as well:
<pre> @takes(foo = str, bar = optional(int)) def foo(**kwargs): return len(kwargs["foo"]) + kwargs.get("bar", 0) </pre>
One more thing that's nice to have is an ability to check protocols, rather that types. This can be done as <pre> @takes(with_attr("write", "flush") def foo(stream): stream.write() stream.flush() </pre>
Any callable can be used as a checker predicate as soon as it returns True/False as appropriate:
<pre> @takes(callable) def foo(c): ... </pre>
<pre> @takes(lambda x: x < 0) def foo(x): ... </pre>
Multiple "or" checks can be applied from a tuple (similar to isinstance() semantics): <pre> @takes((int, long, callable), (str, unicode)) def f(a, b): ... </pre>
Optional parameters can be checked like: <pre> @takes(optional(int, long)) def foo(i = None): ... </pre> where optional(x) is essentially an alias for (x, NoneType)
Likewise, in <pre> @takes(anything) @returns(nothing) def foo(): ... </pre> "anything" is an alias for lambda: True, while "nothing" is an alias for NoneType.
Finally, a few shortcut checkers exist:
<pre> @takes(by_regex("^foo$")) def foo(s): ... </pre>
<pre> @takes(with_attr("write", "flush")) def foo(stream): ... </pre>
<pre> @takes(one_of(1, 2)) def foo(stream): ... </pre>
Checkers can be nested, using the following structural checkers:
<pre> @takes(list_of(int)) def foo(lstint): return lstint[0] + 1 </pre>
<pre> @takes(tuple_of(by_regex("^[0-9]+$"))) def foo(tupstr): return int(tupstr[0]) </pre>
<pre> @takes(dict_of(str, callable)) def foo(callables): return callables"foo" </pre>
<pre> @takes(set_of(str)) def foo(attrs): return "good" in attrs </pre>
Tags: sysadmin
preview is your friend. You should reformat your code snippets in the discussion via <pre>, and verify it looks the way you want it to with the 'preview' button.
Good point. Yes, now it looks much better indeed.
Added predicates. Added a few useful predicates:
@takes(list_of(int))
@takes(tuple_of(int))
@takes(dict_of(str, str))
@takes(by_regex("^[0-9]{1,8}$"))
Added predicate. Added another predicate useful for checking protocol conformance:
@takes(with_attr("read", "write"))
Added one_of checker and support for checking kwargs
You could simplify:
to:
or perhaps:
Similarly for other shortcuts.
Thank you, I have incorporated the simplification you suggest.