This recipe allows nice and clean validation for method parameters/return values. It uses function annotations available in Python 3.0 for the actual signature specification.
| Python |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 | #!/usr/bin/env python
#-*- coding: iso-8859-1 -*-
################################################################################
#
# Parameter/return value type checking for Python 3000 using function annotations.
#
# (c) 2008, Dmitry Dvoinikov <dmitry@targeted.org>
# Distributed under BSD license.
#
# Samples:
#
# from typecheck import *
#
# @typecheck
# def foo(i: int, x = None, s: str = "default") -> bool:
# ...
#
# @typecheck
# def foo(*args, k1: int, k2: str = "default", k3 = None) -> nothing:
# ...
#
# @typecheck
# def foo(ostream: with_attr("write", "flush"), f: optional(callable) = None):
# ...
#
# divisible_by_three = lambda x: x % 3 == 0
# @typecheck
# def foo(i: by_regex("^[0-9]+$")) -> divisible_by_three:
# ...
#
# @typecheck
# def reverse_2_tuple(t: (str, bytes)) -> (bytes, str):
# ...
#
# @typecheck
# def reverse_3_list(t: [int, float, bool]) -> [bool, float, int]:
# ...
#
# @typecheck
# def extract_from_dict(d: dict_of(int, str), k: tuple_of(int)) -> list_of(str):
# ...
#
# @typecheck
# def set_level(level: one_of(1, 2, 3)):
# ...
#
# The (6 times longer) source code with self-tests is available from:
# http://www.targeted.org/python/recipes/typecheck3000.py
#
################################################################################
__all__ = [ "typecheck", "optional", "with_attr", "by_regex", "callable",
"anything", "nothing", "tuple_of", "list_of", "dict_of", "one_of",
"TypeCheckError", "TypeCheckSpecificationError",
"InputParameterError", "ReturnValueError" ]
################################################################################
import inspect
import functools
import re
callable = lambda x: hasattr(x, "__call__")
anything = lambda x: True
nothing = lambda x: x is None
################################################################################
class TypeCheckError(Exception): pass
class TypeCheckSpecificationError(Exception): pass
class InputParameterError(TypeCheckError): pass
class ReturnValueError(TypeCheckError): pass
################################################################################
class Checker(object):
class NoValue:
def __str__(self):
return "<no value>"
no_value = NoValue()
_registered = []
@classmethod
def register(cls, predicate, factory):
cls._registered.append((predicate, factory))
@classmethod
def create(cls, value):
if isinstance(value, cls):
return value
for predicate, factory in cls._registered:
if predicate(value):
return factory(value)
else:
return None
def __call__(self, value):
return self.check(value)
################################################################################
class TypeChecker(Checker):
def __init__(self, cls):
self._cls = cls
def check(self, value):
return isinstance(value, self._cls)
Checker.register(inspect.isclass, TypeChecker)
################################################################################
iterable = lambda x: hasattr(x, "__iter__")
class IterableChecker(Checker):
def __init__(self, cont):
self._cls = type(cont)
self._chks = tuple(Checker.create(x) for x in iter(cont))
def check(self, value):
if not iterable(value):
return False
vals = tuple(iter(value))
return isinstance(value, self._cls) and len(self._chks) == len(vals) and \
functools.reduce(lambda r, c_v: r and c_v[0].check(c_v[1]),
zip(self._chks, vals), True)
Checker.register(iterable, IterableChecker)
################################################################################
class CallableChecker(Checker):
def __init__(self, func):
self._func = func
def check(self, value):
return bool(self._func(value))
Checker.register(callable, CallableChecker)
################################################################################
class OptionalChecker(Checker):
def __init__(self, check):
self._check = Checker.create(check)
def check(self, value):
return value is Checker.no_value or value is None or self._check.check(value)
optional = OptionalChecker
################################################################################
class WithAttrChecker(Checker):
def __init__(self, *attrs):
self._attrs = attrs
def check(self, value):
for attr in self._attrs:
if not hasattr(value, attr):
return False
else:
return True
with_attr = WithAttrChecker
################################################################################
class ByRegexChecker(Checker):
def __init__(self, regex):
self._regex = re.compile(regex)
def check(self, value):
return isinstance(value, str) and self._regex.match(value) is not None
by_regex = ByRegexChecker
################################################################################
class TupleOfChecker(Checker):
def __init__(self, check):
self._check = Checker.create(check)
def check(self, value):
return isinstance(value, tuple) and \
functools.reduce(lambda r, v: r and self._check.check(v), value, True)
tuple_of = TupleOfChecker
################################################################################
class ListOfChecker(Checker):
def __init__(self, check):
self._check = Checker.create(check)
def check(self, value):
return isinstance(value, list) and \
functools.reduce(lambda r, v: r and self._check.check(v), value, True)
list_of = ListOfChecker
################################################################################
class DictOfChecker(Checker):
def __init__(self, key_check, value_check):
self._key_check = Checker.create(key_check)
self._value_check = Checker.create(value_check)
def check(self, value):
return isinstance(value, dict) and \
functools.reduce(lambda r, t: r and self._key_check.check(t[0]) and \
self._value_check.check(t[1]),
value.items(), True)
dict_of = DictOfChecker
################################################################################
class OneOfChecker(Checker):
def __init__(self, *values):
self._values = values
def check(self, value):
return value in self._values
one_of = OneOfChecker
################################################################################
def typecheck(method):
argspec = inspect.getfullargspec(method)
if not argspec.annotations:
return method
default_arg_count = len(argspec.defaults or [])
non_default_arg_count = len(argspec.args) - default_arg_count
method_name = method.__name__
arg_checkers = [None] * len(argspec.args)
kwarg_checkers = {}
return_checker = None
kwarg_defaults = argspec.kwonlydefaults or {}
for n, v in argspec.annotations.items():
checker = Checker.create(v)
if checker is None:
raise TypeCheckSpecificationError("invalid typecheck for {0}".format(n))
if n in argspec.kwonlyargs:
if n in kwarg_defaults and \
not checker.check(kwarg_defaults[n]):
raise TypeCheckSpecificationError("the default value for {0} is incompatible "
"with its typecheck".format(n))
kwarg_checkers[n] = checker
elif n == "return":
return_checker = checker
else:
i = argspec.args.index(n)
if i >= non_default_arg_count and \
not checker.check(argspec.defaults[i - non_default_arg_count]):
raise TypeCheckSpecificationError("the default value for {0} is incompatible "
"with its typecheck".format(n))
arg_checkers[i] = (n, checker)
def typecheck_invocation_proxy(*args, **kwargs):
for check, arg in zip(arg_checkers, args):
if check is not None:
arg_name, checker = check
if not checker.check(arg):
raise InputParameterError("{0}() has got an incompatible value "
"for {1}: {2}".format(method_name, arg_name,
str(arg) == "" and "''" or arg))
for arg_name, checker in kwarg_checkers.items():
kwarg = kwargs.get(arg_name, Checker.no_value)
if not checker.check(kwarg):
raise InputParameterError("{0}() has got an incompatible value "
"for {1}: {2}".format(method_name, arg_name,
str(kwarg) == "" and "''" or kwarg))
result = method(*args, **kwargs)
if return_checker is not None and not return_checker.check(result):
raise ReturnValueError("{0}() has returned an incompatible "
"value: {1}".format(method_name, str(result) == "" and "''" or result))
return result
functools.update_wrapper(typecheck_invocation_proxy, method)
return typecheck_invocation_proxy
################################################################################
# EOF
|
Discussion
With Python 3000's function annotations method signature type checking is much cleaner than with Python 2.x (see at http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/426123).
First, it puts the signature-related piece of syntax exactly where it belongs - near the parameter. Second, you don't have to add checking to all the parameters, but just to those which require checking. Third, it plays nicely with default values.
The typical usage for this decorator would be something like this:
@typecheck
def foo(i: int) -> bool:
return a > 0
@typecheck
def to_int(*, s: by_regex("^[0-9]+$")) -> int:
return int(s)
@typecheck
def set_debug_level(self, level: optional(one_of(1, 2, 3)) = 2):
self._level = level
This recipe is extensible with callable predicates, such as
is_even = lambda x: x % 2 == 0
@typecheck
def multiply_by_2(i: int) -> is_even:
return i * 2
Comments
Did you mean...
Did you mean 's : by_regex' instead of 's = by_regex'?
Yes, you are absolutely right, I meant
with a default value perhaps:
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