DataType of Arguments for Function in Python

Question

Here's a thing I want to predefine DataType of any argument accepts by a Function in python just like we do in C or C++.

# For Example
def maw(x, y):
  return x+y # I want to predefine this x and y to be integer-type

Just like

// This is C-Program which accepts only integer as a parameter
int main(int x, int y){
return x+y;
}

I don't want to Filter this parameter with another line of code like

if 'int' in type(x):
  pass
else:
  return False

Does this answer your question? [Explicitly Define Datatype in Python Function](https://stackoverflow.com/questions/43233535/explicitly-define-datatype-in-python-function) — buran, Mar 13 '21 at 14:51
something like `assert(isinstance(x, int) and isinstance(y, int))` ? — Epsi95, Mar 13 '21 at 14:51
type annotation won't raise error they are just for convenience — Epsi95, Mar 13 '21 at 14:51

score 0 · Answer 1 · answered Mar 13 '21 at 18:01

0

There is no way to declare variables in Python, since neither "declaration" nor "variables" in the C sense exist.

reference

answered Mar 13 '21 at 18:01

Rima

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Peter Badida · Answer 2 · 2021-03-14T09:56:24.773

Type annotation is still only a convenience, unfortunately, though it'd be nice to mandatory enable them by a Python interpreter flag.

However, they can be used for a static analysis with mypy or for a dynamic, runtime analysis (quite efficient for running in combination with unittesting) with ensure.

Taken from ensure's doc:

from ensure import ensure_annotations

@ensure_annotations
def f(x: int, y: float) -> float:
    return x + y

or in your DateType case:

>>> from ensure import ensure_annotations
>>> from datetime import datetime, timedelta
>>> @ensure_annotations
... def myfunc(param: datetime) -> datetime:
...     return 123
... 
>>> @ensure_annotations
... def mycorrectfunc(param: datetime) -> datetime:
...     return param + timedelta(days=1)
... 
>>> myfunc(datetime.now())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../lib/python3.8/site-packages/ensure/main.py", line 855, in __call__
    raise EnsureError(msg.format(
ensure.main.EnsureError: Return value of <function myfunc at 0x7f28325d7310> of type <class 'int'> does not match annotation type <class 'datetime.datetime'>
>>> mycorrectfunc(datetime.now())
datetime.datetime(2021, 3, 15, 10, 53, 37, 888834)
>>>

and this is applicable for all other classes or type aliases (very!) roughly in a similar way typedef or rather assert isinstance(...) are used.

DataType of Arguments for Function in Python

2 Answers2