Implement str.format()

[trotterdylan]

There's a lot stdlib code (especially in the unittest library) that uses str.format() so this will become very important soon.

[S-YOU]

Yeah, hit that a lot when adding new modules.

[S-YOU]

I think we have three options.

• port CPython C version to go
• port pypy's newformat as python library.
• use external stringformat library as python library.

What would be Ideal solution? I guess CPython version?

[trotterdylan]

I think newformat will be problematic because of all the pypy specific extensions used in that file.

The stringformat lib is a good find! It would require a little hackery because the grumpy Go package would need to somehow patch str.format with the generated code for stringformat.py. But it is doable and it could be a good stopgap until we can implement something ourselves.

[S-YOU]

Monkey-patching method on builtins is easier on grumpy than (CPython](https://gist.github.com/mahmoudimus/295200)

Can we keep as a feature or will forbid like CPython?

str.__dict__["format"] = lambda self: "formatted: " + self
print "hello".format()

formatted: hello