In Python 2.7:
In [2]: utf8_str = '\xf0\x9f\x91\x8d' In [3]: print(utf8_str) 👍 In [4]: unicode_str = utf8_str.decode('utf-8') In [5]: print(unicode_str) 👍 In [6]: unicode_str Out[6]: u'\U0001f44d' In [7]: len(unicode_str) Out[7]: 2 Since unicode_str only contains a single unicode code point (0x0001f44d), why does len(unicode_str) return 2 instead of 1?
Your Python binary was compiled with UCS-2 support (a narrow build) and internally anything outside of the BMP (Basic Multilingual Plane) is represented using a surrogate pair.
That means such codepoints show up as 2 characters when asking for the length.
You'll have to recompile your Python binary to use UCS-4 instead if this matters (./configure --enable-unicode=ucs4 will enable it), or upgrade to Python 3.3 or newer, where Python's Unicode support was overhauled to use a variable-width Unicode type that switches between ASCII, UCS-2 and UCS-4 as required by the codepoints contained.
On Python versions 2.7 and 3.0 - 3.2, you can detect what kind of build you have by inspecting the sys.maxunicode value; it'll be 2^16-1 == 65535 == 0xFFFF for a narrow UCS-2 build, 1114111 == 0x10FFFF for a wide UCS-4 build. In Python 3.3 and up it is always set to 1114111.
Demo:
# Narrow build $ bin/python -c 'import sys; print sys.maxunicode, len(u"\U0001f44d"), list(u"\U0001f44d")' 65535 2 [u'\ud83d', u'\udc4d'] # Wide build $ python -c 'import sys; print sys.maxunicode, len(u"\U0001f44d"), list(u"\U0001f44d")' 1114111 1 [u'\U0001f44d'] 
sys.maxunicode on Python 3 too. It is implied but it is worth pointing out it explicitly that len(u'\U0001f44d') == 1 on Python 3.3+ (or a wide Python 2 build)
sys.maxunicode regardless of the version.
sys.maxunicode value to be 1114111, but still the length of this emoji/string is still displaying as 2 :_(