What is the relationship between __repr__ and eval(), and what is the main purpose of __repr__?
python, python-3.x
Solution
For types that have a literal notation (`str`, `int`, `float`, `list`, etc.) the `repr()` returns a string that can be used to create the type again.
That is nice, but not a requirement.
The main purpose for `__repr__` is to provide the developer with unambiguous information as to what object they have here, for debugging purposes.
Quoting from the `__repr__` documentation:
Called by the `repr()` built-in function to compute the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form `<...some useful description...>` should be returned.
but most of all:
This is typically used for debugging, so it is important that the representation is information-rich and unambiguous.
Emphasis mine.
Returning a constant string from your custom type would not break anything technically, but would make your life as a developer harder.
Problem
I just came across this question Difference between `__str__` and `__repr__` in Python and its mentioned that the main purpose of the `__repr__` is to be unambiguous. But I heard that the main purpose of the `__repr__` is to generate a string such that `eval()` can reconstruct the python object later. Actually what is the main purpose of `__repr__`? Do any built-in functions or any default modules in python inherently use `__repr__` to reconstruct the object? Will it mess up the execution if we just overwrite `__repr__` such that it returns a constant string (e.g. "foo") always?