SyntaxError: encoding declaration in Unicode string

Question

If I try to use a magic comment like #coding=utf-8 on top of a file, here's what happens:

Traceback (most recent call last):
  File <string>, line 0
SyntaxError: encoding declaration in Unicode string

I really haven't done anything wrong. Here is the code:

#coding=utf-8

string = raw_input()
chars = {}
for i in string:
    if i in chars:
        chars[i] += 1
    else:
        chars[i] = 0
print chars

I use repl.it.

Answer 1

You omitted something from your question: You are using exec to execute this code. And you passed a Unicode object to exec, which means you already have stated that the source is Unicode text:

>>> code = '''\
... # coding=utf8
... print 'hello world!'
... '''
>>> exec code
hello world!
>>> exec code.decode('utf8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 0
SyntaxError: encoding declaration in Unicode string

You can't use a PEP 263 declaration in Unicode text passed to exec.

If you are using a 'custom' environment like repl.it, then yes, such environments invariably use tricks like exec to execute code, and they load the source code as Unicode from your browser. See the actual code used, which passes JSON-sourced strings to exec (where such strings are always going to be unicode strings).