Variables

Local SmartPy variables can be defined as follows: x = sp.local("x", 0)

The first argument to sp.local is a string that will be used in error messages. It is advisable to use the same name that is used on the left of =.

Local variable values can be accessed to and updated with the .value field: x.value = 1, x.value = 2 * x.value + 5.

Local variables are necessary when the variable is mutated inside if's and loop's.

Local variables can be marked as immutable by specifying mutable = False.

Local SmartPy variables are different from Python

variables. The latter cannot be updated during contract execution. :::

As an example, here is how we can compute a square root.

python

@sp.entrypoint
def squareRoot(self, x):
    sp.verify(x >= 0)
    y = sp.local('y', x)
    sp.while y.value * y.value > x:
        y.value = (x // y.value + y.value) // 2
    sp.verify((y.value * y.value <= x) & (x < (y.value + 1) * (y.value + 1)))
    self.data.value = y.value

Variables ​

Variables