[all-commits] [llvm/llvm-project] c7a56a: [lldb][bindings] Implement __repr__ instead of __s...

[Dave Lee via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c7a56af3072c2fa89f0968d7f00b22f7bff0812b
      https://github.com/llvm/llvm-project/commit/c7a56af3072c2fa89f0968d7f00b22f7bff0812b
  Author: Dave Lee <davelee.com at gmail.com>
  Date:   2022-06-11 (Sat, 11 Jun 2022)

  Changed paths:
    M lldb/bindings/macros.swig
    A lldb/test/API/sanity/TestReprStrEquality.py
    M lldb/test/Shell/Driver/Inputs/convenience.in
    M lldb/test/Shell/Driver/TestConvenienceVariables.test

  Log Message:
  -----------
  [lldb][bindings] Implement __repr__ instead of __str__

When using the `script` Python repl, SB objects are printed in a way that gives
the user no information. The simplest example is:

```
(lldb) script lldb.debugger
<lldb.SBDebugger; proxy of <Swig Object of type 'lldb::SBDebugger *' at 0x1097a5de0> >
```

This output comes from the Python repl printing the `repr()` of an object.

None of the SB classes implement `__repr__`, and all print like the above.
However, many (most?, all?) SB classes implement `__str__`. Because they
implement `__str__`, a more detailed output can be had by `print`ing the
object, for example:

```
(lldb) script print(lldb.debugger)
Debugger (instance: "debugger_1", id: 1)
```

For convenience, this change switches all SB classes that implement to
`__str__` to instead implement `__repr__`. **The result is that `str()` and
`repr()` will produce the same output**. This is because `str` calls `__repr__`
for classes that have  no `__str__` method.

The benefit being that when writing a `script` invocation, you don't need to
remember to wrap in `print()`. If that isn't enough motivation, consider the
case where your Python expression results in a list of SB objects, in that case
you'd have to `map` or use a list comprehension like `[str(x) for x in <expr>]`
in order to see the details of the objects in the list.

For reference, the docs for `repr` say:

> repr(object)
>   Return a string containing a printable representation of an object. For
>   many types, this function makes an attempt to return a string that would
>   yield an object with the same value when passed to eval(); otherwise, the
>   representation is a string enclosed in angle brackets that contains the
>   name of the type of the object together with additional information often
>   including the name and address of the object. A class can control what this
>   function returns for its instances by defining a __repr__() method.

and the docs for `__repr__` say:

> object.__repr__(self)
>   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. The
>   return value must be a string object. If a class defines __repr__() but not
>   __str__(), then __repr__() is also used when an “informal” string
>   representation of instances of that class is required.
>
>   This is typically used for debugging, so it is important that the
>   representation is information-rich and unambiguous.

Even if it were convenient to construct Python expressions for SB classes so
that they could be `eval`'d, however for typical lldb usage, I can't think of a
motivating reason to do so. As it stands, the only action the docs say to do,
that this change doesn't do, is wrap the `repr` string in `<>` angle brackets.

An alternative implementation is to change lldb's python repl to apply `str()`
to the top level result. While this would work well in the case of a single SB
object, it doesn't work for a list of SB objects, since `str([x])` uses `repr`
to convert each list element to a string.

Differential Revision: https://reviews.llvm.org/D127458