How can I determine the byte length of a utf-8 encoded string in Python?

Question

I am working with Amazon S3 uploads and am having trouble with key names being too long. S3 limits the length of the key by bytes, not characters.

From the docs:

Answer 1

Use the string 'encode' method to convert from a character-string to a byte-string, then use len() like normal:

>>> s = u"¡Hola, mundo!"                                                      
>>> len(s)                                                                    
13 # characters                                                                             
>>> len(s.encode('utf-8'))   
14 # bytes