C code continues to follow PEP 7. C++ should follow PEP 7 as much as possible. For things PEP 7 doesn't cover, try to follow the LLVM style guide. For things that neither the LLVM style guide nor PEP 7 cover, consult the Google C++ style guide. We also have a few rules below for things they don't cover.

Always use this.

In C++, inside a class, you're allowed to call member functions and access member variables without explicitly using the this keyword. We prefer to keep things explicit for three reasons.

1. Python requires self, so requiring this is consistent.
2. It's easier to know where to look for a function when the prefix tells you where it lives.
3. There are certain cases in C++ where `this` is required, and always requiring it avoids confusion when you run into those cases.

Don't throw exceptions.

We don't throw exceptions because so much CPython code isn't exception safe. However, we may start catching particular exceptions thrown by the standard library like std::bad_alloc in order to convert them to a form Python can deal with inside the language.

Capitalization

Class and struct names, member function names (all of public, private, and static), PyPublic_Function, and _PyInternal_Function names should all be CamelCased. Static functions within a .cc file are lower_case_with_underscores. Variable names are lower_case_with_underscores. Member variable names end_with_an_underscore_.

Smart Pointers

For now, we're only using llvm::OwningPtr (and OwningArrayPtr). std::auto_ptr does nearly the same thing, but has confusing assignment and copy construction semantics, so we're avoiding it. We don't have a smart pointer for Python refcounting because we couldn't use it in the C code anyway, and we haven't yet discussed the requirements for a non-PyObject refcounting pointer.

C++ is Optional

Any C++ used in Unladen Swallow should be disabled when configured with --without-llvm. Accordingly, any C++ should be guarded with #ifdef WITH_LLVM.