Control statements

Since Python doesn't allow its control statements to be overloaded, SmartPy uses its own control statements for statements that need to be executed on-chain.

Internally, we use with-blocks introduced by sp.if_, sp.else_, sp.for_ and sp.while_.
These constructions are regular Python and can be used directly. In practice, they are usually preferred by power-users and are also much more IDE-friendly.

We also pre-process the SmartPy script for sugared versions: sp.if, sp.else, sp.for, sp.while.

If statement

A if condition that is evaluated on-chain.

python

sp.if x == 10 :
    self.data.result = 0
sp.else:
    self.data.result += x

The desugared version is

python

with sp.if_(x == 10):
    self.data.result = 0
with sp.else_():
    self.data.result += x

If we use e.g. sp.if instead of a plain if, the result

will be a SmartPy conditional instead of a Python one.

SmartPy conditionals are executed once the contract has been constructed and has been deployed or is being simulated. On the other hand, Python conditionals are executed immediately. Therefore the condition after the if cannot depend on the state of the contract.

When in doubt, it is reasonable to use the sp. prefix inside a smart contract. :::

Michelson IF

For statement

A for loop that is evaluated on-chain.

python

sp.for x in params:
    self.data.result += x

The desugared version is

python

with sp.for_("x", params) as x:
    self.data.result += x

Michelson ITER

and

Michelson MAP

While statement

A while loop that is evaluated on-chain.

python

sp.while 1 < y.value:
    self.data.value += 1
    y.value //= 2

The desugared version is

python

with sp.while_(1 < y.value):
    self.data.value += 1
    y.value //= 2

Michelson LOOP

Control statements ​

If statement ​

For statement ​

While statement ​

Control statements

If statement

For statement

While statement