Python repr for classes

Question

As the Python 2 documentation on `__repr__` states: If at all possible, this (i.e. `__repr__`) should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). So how come builtin `__repr__` for classes does not act accordingly to that guideline? Example ``` >>> class A(object): ... pass >>> repr(A) "<class 'A'>" ``` To meet the guideline, the default `__repr__` should return `"A"`, i.e. generally `A.__name__`. Why is it acting differently? It would be extra-easy to implement, I believe. Edit: The scope of 'reproduction' I can see in the answers that it is not clear in the discussion what `repr` should return. The way I see it, the `repr` function should return a string that allows you to reproduce the object: - in an arbitrary context and - automatically (i.e. not manually). Ad.1. Take a look at a built-in class case (taken from this SO question): ``` >>> from datetime import date >>> >>> repr(date.today()) #…

Accepted Answer

Consider a slightly more complicated class:

```
class B(object):
    def __init__(self):
        self.foo=3
```

`repr` would need to return something like

```
type("B", (object,), { "__init__": lambda self: setattr(self, "foo", 3) })
```

Notice one difficulty already: not all functions defined by the `def` statement can be translated into a single `lambda` expression. Change `B` slightly:

```
class B(object):
    def __init__(self, x=2, y, **kwargs):
        print "in B.__init__"
```

How do you write an expression that defines `B.__init__`? You can't use

```
lambda self: print "in B.__init__"
```

because `lambda` expressions cannot contain statements. For this simple class, it is already impossible to write a single expression that defines the class completely.

Python repr for classes

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