Method add

src/urllib3/_collections.py:306–339

Adds a (name, value) pair, doesn't overwrite the value if it already exists. If this is called with combine=True, instead of adding a new header value as a distinct item during iteration, this will instead append the value to any existing header value with a comma. I

(self, key: str, val: str, *, combine: bool = False)

            pass

    def add(self, key: str, val: str, *, combine: bool = False) -> None:
        """Adds a (name, value) pair, doesn't overwrite the value if it already
        exists.

        If this is called with combine=True, instead of adding a new header value
        as a distinct item during iteration, this will instead append the value to
        any existing header value with a comma. If no existing header value exists
        for the key, then the value will simply be added, ignoring the combine parameter.

        >>> headers = HTTPHeaderDict(foo='bar')
        >>> headers.add('Foo', 'baz')
        >>> headers['foo']
        'bar, baz'
        >>> list(headers.items())
        [('foo', 'bar'), ('foo', 'baz')]
        >>> headers.add('foo', 'quz', combine=True)
        >>> list(headers.items())
        [('foo', 'bar, baz, quz')]
        """
        # avoid a bytes/str comparison by decoding before httplib
        if isinstance(key, bytes):
            key = key.decode("latin-1")
        key_lower = key.lower()
        new_vals = [key, val]
        # Keep the common case aka no item present as fast as possible
        vals = self._container.setdefault(key_lower, new_vals)
        if new_vals is not vals:
            # if there are values here, then there is at least the initial
            # key/value pair
            assert len(vals) >= 2
            if combine:
                vals[-1] = vals[-1] + ", " + val
            else:
                vals.append(val)

    def extend(self, *args: ValidHTTPHeaderSource, **kwargs: str) -> None:
        """Generic import function for any type of header-like object.