erg/doc/EN/syntax/32_integration_with_Python.md

Integration with Python

All objects imported from Python are by default of type Object. Since no comparisons can be made at this point, it is necessary to refine the type.

Type Specification in the Standard Library

All APIs in the Python standard library are type specified by the Erg development team.

time = pyimport "time"
time.sleep! 1

Type Specification for User Scripts

Create a foo.d.er file that types the Python foo module. Type hints on the Python side are ignored since they are not 100% guaranteed.

# foo.py
X = ...
def bar(x):
    ...
def baz():
    ...
...

# foo.d.er
foo = pyimport "foo"
.X = declare foo.'X', Int
.bar = declare foo.'bar', Int -> Int
.baz! = declare foo.'baz', () => Int

foo = pyimport "foo"
assert foo.bar(1) in Int

This ensures type safety by performing type checking at runtime. The declare function works roughly as follows.

declare|S: Subroutine| sub!: S, T =
    # Actually, => can be cast to a function without block side effects
    x =>
        assert x in T.Input
        y = sub!(x)
        assert y in T.Output
        y

Since this is a runtime overhead, a project is planned to statically type analyze Python scripts with Erg's type system.

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