Programming by contract library.
Project description
Deal – python library for design by contract (DbC) programming.
This library contain 3 main conception from DbC:
Precondition – condition that must always be true just prior to the execution of function.
Postcondition – condition that must always be true just after the execution of function.
Invariant – condition that can be relied upon to be true during execution of a program. In this library invariant condition check in 3 cases:
Before class method execution.
After class method execution.
After some class attribute setting.
Features
Functional declaration for conditions.
Custom exceptions for best usage in try-except block.
Ability to set optional error message and (or) exception class.
Ability to return error message from contact.
Ability to use Django Form styled validators as contracts.
Attribute setting validation by invariant.
Validation by invariant dynamically assigned to object attributes and methods.
Readable source code (all decorators implemented by classes)
Installation
Stable:
pip install dealDev:
pip install -e git+https://github.com/orsinium/deal.git#egg=dealTL;DR
@pre – validate function arguments (pre-validation).
@post – validate function result (post-validation).
@inv – validate class methods before and after some method calling and after attribute setting.
Exceptions structure:
ContractError (inherited from built-in AssertionError)
PreContractError
PostContractError
InvContractError
Library decorators doesn’t catch any exceptions raised from contracts.
Usage
Pre (pre, require):
In [1]: from deal import pre, post, inv, ContractError
In [2]: @pre(lambda *args: all(map(lambda x: x > 0, args)))
...: def my_sum(*args):
...: return sum(args)
...:
In [3]: my_sum(2, 3, 4)
Out[3]: 9
In [4]: my_sum(2, -3, 4)
PreContractError:Post (post, ensure):
In [5]: @post(lambda x: x > 0)
...: def my_sum(*args):
...: return sum(args)
...:
In [6]: my_sum(2, -3, 4)
Out[6]: 3
In [7]: my_sum(2, -3, -4)
PostContractError:Inv (inv, invariant):
In [8]: @inv(lambda obj: obj.x > 0)
...: class A:
...: x = 4
...:
In [9]: a = A()
In [10]: a.x = 10
In [11]: a.x = -10
InvContractError:
In [12]: A
Out[12]: deal.core.AInvariantedCustom message:
In [13]: @pre(lambda x: x > 0, "x must be > 0")
...: def f(x):
...: return x * 2
...:
In [14]: f(-2)
PreContractError: x must be > 0Custom exception:
In [15]: @pre(lambda x: x > 0, exception=AssertionError("x must be > 0"))
...: def f(x):
...: return x * 2
...:
In [16]: f(-2)
AssertionError: x must be > 0Validators (nearly Django Forms style, except initialization):
In [17]: class Validator:
...: def __init__(self, x):
...: self.x = x
...:
...: def is_valid(self):
...: if self.x <= 0:
...: self.errors = ['x must be > 0']
...: return False
...: return True
...:
In [18]: @pre(Validator)
...: def f(x):
...: return x * 2
...:
In [19]: f(5)
Out[19]: 10
In [20]: f(-5)
PreContractError: ['x must be > 0']Return error message from contract:
In [21]: @pre(lambda x: x > 0 or "x must be > 0")
...: def f(x):
...: return x * 2
...:
In [22]: f(-5)
PreContractError: x must be > 0Contracts chaining:
In [23]: @pre(lambda x: x > 0)
...: @pre(lambda x: x < 10)
...: def f(x):
...: return x * 2
...:
In [24]: f(5)
Out[24]: 10
In [25]: f(-1)
PreContractError:
In [26]: f(12)
PreContractError:Contracts chaining order
@inv: from top to bottom.
@pre: from top to bottom.
@post: from bottom to top.
Perfomance
NOTICE: 1 µs == 1000 ns
@pre and @post:
In [27]: f = lambda x: x
In [28]: pre_f = pre(lambda x: True)(f)
In [29]: post_f = post(lambda x: True)(f)
In [30]: %timeit f(10)
92.3 ns ± 3.62 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
In [31]: %timeit pre_f(10)
2.07 µs ± 92.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
In [32]: %timeit post_f(10)
2.03 µs ± 18.6 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)+1 µs
@inv:
In [33]: class A:
...: x = 4
...:
In [34]: InvA = inv(lambda obj: True)(A)
In [35]: a = A()
In [36]: inv_a = InvA()
In [37]: %timeit a.x = 10
76.4 ns ± 1.36 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
In [38]: %timeit inv_a.x = 10
6.89 µs ± 408 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)+6 µs
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