Python Unicode Tutorial 🐍

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If you are not familiar with Unicode, first see: Unicode Basics: What's Character Set, Character Encoding, UTF-8?

Unicode Characters in Source Code

What's Python source code's default encoding?

For Python 2.x, it's ASCII.

For Python 3.x, it's UTF-8.

Python 2: If your source code contains Unicode characters, you must declare the file's encoding -*- coding: utf-8 -*- in the first line or second line. Like this:

#-*- coding: utf-8 -*-
# python 2
u"I β™₯ Cats"

The #-*- coding: utf-8 -*- declaration in the first line is a convention adopted from the text editor Emacs. γ€”βž€Β Emacs and Unicode Tips〕 It tells any program reading the file that the file is encoded using a particular character set. Its purpose is similar to HTML's <meta http-equiv="content-type" content="text/html; charset=utf-8" />. (See: Character Sets and Encoding in HTML β—‡ UNICODE Basics.) This convention is also used by Ruby. γ€”βž€Β Ruby Unicode Tutorial πŸ’Žγ€•

Python 2: Declare Unicode String

For Python 2, strings that contain Unicode characters must start with u in front of the string. Example:

#-*- coding: utf-8 -*-
# python 2

aa = u"I β™₯ U"     # unicode string, start with β€œu” or β€œur”

print(aa)         # I β™₯ U

The u makes the string a Unicode datatype. Without the u, string is just byte sequence.

Sometimes when you print Unicode strings, you may get a error like this:

# UnicodeEncodeError: 'ascii' codec can't encode character u'\u03b1' in position 16: ordinal not in range(128).

The solution is to use the .encode() or .decode() method. Example:

#-*- coding: utf-8 -*-
# python 2

myStr = u'Ξ±'

# # Bad. This is a error.
print 'Greek alpha: ', myStr

# Good
print 'Greek alpha: ', myStr.encode('utf-8')

Unicode in Regex

When using regex on Unicode string, and you want the patterns {\w, \W, \b, \B} dependent on the Unicode character properties , you need to add the Unicode flag re.U when calling regex functions.

# -*- coding: utf-8 -*-
# python 2

import re

rr = re.search(r"\w+", u"β™₯Ξ±Ξ²Ξ³!", re.U)

if rr:
    print rr.group().encode("utf8")
else:
    print "no match"

# prints γ€ŒΞ±Ξ²Ξ³γ€

# if re.U is not used, it prints γ€Œno match」 because the γ€Œ\w+」 pattern for β€œword” only consider ASCII letters

See: Python Regex Flags.

Unicode in Python 3

In Python 3, everything is Unicode (UTF-8). You do not need to use # -*- coding: utf-8 -*-, nor need to have u"…" in string.

Python 3 supports Unicode in variable οΌ† function names.

# -*- coding: utf-8 -*- ← optional, but still good to indicate encoding
# python 3

def Ζ’(n):
    return n+1

Ξ± = 4
print(Ζ’(Ξ±))                     # prints 5
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