Those are annotations. They tell the programmer what argument types are expected and what type is returned by the function. There are also static analysis tools that use the annotation information to identify potential bugs in you Python code.
The annotations do not affect the execution of a Python program. echo(123) is a valid Python statement that will run up to the point where some operation is performed on "text" that is not valid for an int.
Error:
>>> echo(123)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Users\djhys\Documents\python\musings\echo.py", line 5, in echo
echoed_text += f"{text[-i:]}\n"
~~~~^^^^^
TypeError: 'int' object is not subscriptable
A static analysis tool, like mypy, can spot this error before the code is executed.
file test.py
from echo import echo
echo(123)
Runing mypy from cmd shell.
Output:
(env) > mypy junk.py
test.py:3: error: Argument 1 to "echo" has incompatible type "int"; expected "str" [arg-type]
Found 1 error in 1 file (checked 1 source file)
"-> str" tells Python that the function returns a str object.
More about annotations:
https://www.geeksforgeeks.org/function-a...ns-python/
