Class _FuncBuilder

Lib/dataclasses.py:436–533

class _FuncBuilder:
    def __init__(self, globals):
        self.names = []
        self.src = []
        self.globals = globals
        self.locals = {}
        self.overwrite_errors = {}
        self.unconditional_adds = {}
        self.method_annotations = {}

    def add_fn(self, name, args, body, *, locals=None, return_type=MISSING,
               overwrite_error=False, unconditional_add=False, decorator=None,
               annotation_fields=None):
        if locals is not None:
            self.locals.update(locals)

        # Keep track if this method is allowed to be overwritten if it already
        # exists in the class.  The error is method-specific, so keep it with
        # the name.  We'll use this when we generate all of the functions in
        # the add_fns_to_class call.  overwrite_error is either True, in which
        # case we'll raise an error, or it's a string, in which case we'll
        # raise an error and append this string.
        if overwrite_error:
            self.overwrite_errors[name] = overwrite_error

        # Should this function always overwrite anything that's already in the
        # class?  The default is to not overwrite a function that already
        # exists.
        if unconditional_add:
            self.unconditional_adds[name] = True

        self.names.append(name)

        if annotation_fields is not None:
            self.method_annotations[name] = (annotation_fields, return_type)

        args = ','.join(args)
        body = '\n'.join(body)

        # Compute the text of the entire function, add it to the text we're generating.
        self.src.append(f'{f' {decorator}\n' if decorator else ''} def {name}({args}):\n{body}')

    def add_fns_to_class(self, cls):
        # The source to all of the functions we're generating.
        fns_src = '\n'.join(self.src)

        # The locals they use.
        local_vars = ','.join(self.locals.keys())

        # The names of all of the functions, used for the return value of the
        # outer function.  Need to handle the 0-tuple specially.
        if len(self.names) == 0:
            return_names = '()'
        else:
            return_names  =f'({",".join(self.names)},)'

        # txt is the entire function we're going to execute, including the
        # bodies of the functions we're defining.  Here's a greatly simplified