Contract style params for python

pycontracts.py

from functools import wraps
from inspect import getcallargs


def assert_params(*contracts):
    _contracts = []
    for contract in contracts:
        _contracts.append((contract, compile(contract, '', 'eval')))

    def decorator(fn):
        @wraps(fn)
        def new_fn(*args, **kw):
            callargs = getcallargs(fn, *args, **kw)
            for contract in _contracts:
                res = eval(contract[1], callargs)
                assert res, "Contract assertion failed: %s" % contract[0]
            return fn(*args, **kw)
        return new_fn
    return decorator


@assert_params('mork > 10', 'isinstance(baz, str)')
def foo(mork, baz=''):
    print mork

foo(11, '')

try:
    foo(1, '')  # Fails
except Exception as e:
    print e

try:
    foo(11, 1)  # Fails
except Exception as e:
    print e