Valid Code

No Classes Allowed!

Contracting maintains a strict 'no classes' model. This forces you as the developer to create more procedural code that is explicit and completely self-contained. Contracts must be easy to read and understand for validity. Instead of thinking of your code in classes, think of each contract as a 'module' that exposes certain functions to its users.

All class keywords will fail your contract on submission. Even if you try to use classes for object oriented code, you will have to find another way to express your structures.

For example:

class Car:
	def __init__(self, make, model):
		self.make = make
		self.model = model

This is illegal. Instead, describe objects in dictionary formats. If you tend to use classes to encapsulate data, simply use Python dictionaries instead. This is especially useful because of Contracting's storage model that makes it easy to store dictionaries.

cars = Hash()
cars['balthasar'] = {
	'make': 'Ford',
	'model': 'Contour'
}

Read more about storage in the Storage section.

Notable Restricted Builtins

Here are some notable ones with reasons for their restriction:

Built-In	Reason for Restriction
callable()	Functions are not passed as objects in Contracting.
classmethod()	Classes are disabled in Contracting.
compile()	Arbitrary code execution is a high security risk.
complex()	Complex numbers are potentially non-deterministic. This is a consensus failure risk.
delattr()	Arbitrary removal of Python attributes could allow unauthorized access to private objects and methods.
dir()	Allows exploration path into security exploit development.
enumerate()	Not included in the allowed list.
eval()	Arbitrary code execution is a high security risk.
exec()	Arbitrary code execution is a high security risk.
float()	Floating point precision issues can lead to consensus failures.
getattr()	Arbitrary access to attributes could allow private function execution.
globals()	Access to global scope methods allows modification of private methods and direct storage mechanisms.
hasattr()	Allows exploration path into security exploit development.
hash()	Potentially non-deterministic outcomes. Consensus failure risk.
id()	Potentially non-deterministic outcomes. Consensus failure risk.
input()	User input not supported.
iter()	Potential mutation of objects that are only supposed to be interfaced with through particular methods.
locals()	Access to local scope methods allows modification of private methods.
memoryview()	Potentially non-deterministic outcomes. Consensus failure risk.
next()	Related to iter(), not included in the allowed list.
object()	Base class for all classes, not needed since classes are disabled.
open()	File I/O not supported.
property()	Property creation not supported because classes are disabled.
repr()	Potentially non-deterministic due to memory address as output. Consensus failure risk.
setattr()	Arbitrary setting of Python attributes has storage corruption and private method access implications.
staticmethod()	Static methods are not supported because classes are disabled.
super()	Super is not supported because classes are disabled.
vars()	Allows exploration path into security exploit development.

Note: All exceptions except the base Exception class are also removed from Contracting.

Illegal AST Nodes

The Contracting linter restricts certain Python syntax by checking for specific AST (Abstract Syntax Tree) nodes. The following AST nodes are explicitly forbidden:

AST Node	Reason for Restriction
ast.AsyncFor	All async code is invalid in Contracting. Async operations are non-deterministic.
ast.AsyncFunctionDef	All async code is invalid in Contracting. Async operations are non-deterministic.
ast.AsyncWith	All async code is invalid in Contracting. Async operations are non-deterministic.
ast.Await	All async code is invalid in Contracting. Async operations are non-deterministic.
ast.ClassDef	Classes are disabled in Contracting to enforce procedural programming.
ast.Ellipsis	Ellipsis should not be defined in a smart contract. They may be an effect of one.
ast.GeneratorExp	Generators hold state that is incompatible with Contracting's deterministic execution model.
ast.Global	Scope modification could have security implications by allowing access to variables outside the intended scope.
ast.ImportFrom	Selective importing is not supported to prevent importing potentially dangerous modules.
ast.Interactive	Only available in Python interpreters. Potential security risk.
ast.Lambda	Lambda functions can hide complex logic and make contracts harder to audit.
ast.MatMult	Matrix multiplication operator (@) is not supported.
ast.Nonlocal	Scope modification could have security implications by allowing access to variables outside the intended scope.
ast.Suite	Similar to ast.Interactive, not needed in contract code.
ast.Try	Exception handling can lead to non-deterministic execution paths.
ast.With	Context managers can have side effects that are difficult to predict.
ast.Yield	Generator related code is not compatible with Contracting's deterministic execution model.
ast.YieldFrom	Generator related code is not compatible with Contracting's deterministic execution model.

Violations

The linter will check for several violations that will fail your smart contract automatically. Here is a list of the current violations and examples of code that will cause them.

S1- Illegal contracting syntax type used

Thrown when an AST type that is not allowed is visited by the linter.

2 @ 2  # ast.MatMult code

S2- Illicit use of '_' before variable

_ is used for gating certain functionality. Using it as a prefix to any variable will fail.

_balances = Hash()

S3- Illicit use of Nested imports

import keywords found inside of functions, loops, etc. will fail.

import this_wont_fail

@construct
def seed():
    import this_will  # This will fail

S4- ImportFrom compilation nodes not yet supported

Selective importing is not supported and will fail contracts.

from token import send  # This will fail

S5- Contract not found in lib

Not currently used.

S6- Illicit use of classes

Classes are not supported in Contracting and their keywords will fail your contract.

class Car:  # This will fail
    def __init__(self, make, model):
        self.make = make
        self.model = model

S7- Illicit use of Async functions

Any async related code will fail the contract.

async def fail_me():  # This will fail
    pass

S8- Invalid decorator used

@export and @construct are the only two decorators allowed in Contracting.

v = Variable()
@construct
def seed():
    v.set(100)

@export
def get_v():
    return v.get()

@unknown  # This will fail
def this_will_fail():
    pass

S9- Multiple use of constructors detected

Only a single @construct can be included in a contract.

v = Variable()
@construct
def seed():
    v.set(123)

@construct  # This will fail
def seed_2():
    v.set(999)

S10- Illicit use of multiple decorators

Stacking decorators is not allowed.

v = Variable()
@export
@construct  # This will fail
def seed():
    v.set(777)

S11- Illicit keyword overloading for ORM assignments

ORM arguments are injected into the __init__ function on runtime. Messing with these will fail your contract.

v = Variable(contract='token')  # This will fail
w = Variable(driver=None)  # This will fail
x = Variable(another_kwarg='this will fail')  # This will fail

@export
def set():
    v.set(777)
    w.set(999)
    x.set(123)

S12- Multiple targets to ORM definition detected

Python allows multiple assignment. Trying to do a multiple assignment from an ORM object will fail your contract.

x, y = Hash()  # This will fail
@export
def set():
    x['bill'] = 100
    y['bill'] = 999

S13- No valid contracting decorator found

A contract without a single @export decorator is invalid.

@construct
def seed():
    pass
# This will fail because there's no @export function

S14- Illegal use of a builtin

Referencing a builtin that is illegal will fail the contract.

@export
def credits():
    return credits  # This will fail

S15- Reuse of ORM name definition in a function definition argument name

Reuse of any ORM names in any loops, functions, etc. will fail the contract.

used_once = Variable()

@export
def override(used_once):  # This will fail
    return used_once

S16- Illegal argument annotation used

Only certain types are allowed for argument annotations. The allowed types are:

'dict', 'list', 'str', 'int', 'float', 'bool', 'datetime.timedelta', 'datetime.datetime', 'Any'

@export
def invalid_annotation(x: complex):  # This will fail
    return x

S17- No valid argument annotation found

Missing argument annotations will fail the contract.

@export
def missing_annotation(x):  # This will fail
    return x

S18- Illegal use of return annotation

Return annotations are not allowed in Contracting.

@export
def invalid_return() -> int:  # This will fail
    return 42

S19- Illegal use of a nested function definition

Nested functions are not allowed in Contracting.

@export
def outer_function():
    def inner_function():  # This will fail
        return 42
    return inner_function()