uuid.uuid4().hex, used in Element.__init__ to define self._id, is considerably slower than binascii.hexlify(os.urandom(16)).decode(). uuid4 uses os.urandom(16) under the hood when creating a cryptographically-secure UUID, so creating UUIDs for Element-class objects using hexlify leads to a dramatic speed-up (I found about ~60%), which has implications for subclasses of Element. No new requirements are needed as binascii is already in the Python standard library, so this is essentially a free, pretty big speed bump (especially when considering that some Element subclasses in folium themselves create child instances of Element when instantiated).

• self._id = uuid4().hex:

In [1]: from branca.element import Element
   ...: %timeit -n 1000000 Element()
2.5 µs ± 8.56 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

• self._id = hexlify(urandom(16)).decode():

In [1]: from branca.element import Element
   ...: %timeit -n 1000000 Element()
1.06 µs ± 1.86 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)