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safest python encoding across platforms

I will have to run some python code across platforms.
What is the safest option in term of encoding for the source files?
I have noticed that:
#!/bin/env python
# -*- coding: iso-8859-1 -*-
"""
Created on Wed Feb 22 09:40:16 2017
"""
pycode
does not raise errors in Linux, while it does in Windows.
The following seems safer, why is that the case?
#!/bin/env python
#-*- coding: utf-8 -*-
"""
Created on Wed Feb 22 09:40:16 2017
"""
pycode

Python 3 source code is expected to be encoded as UTF-8 by default. Therefore UTF-8 is the safest encoding to use for Python 3 code because developers do not have to remember to do anything - such as declaring a spec
it's the default, so developers do not need to remember to declare an explicit encoding
it can encode any unicode codepoint, so there is (theoretically) no risk that a developer might use a different encoding in a particular source to include a particular character
However, if the source code is edited on systems where UTF-8 is not the default encoding, developers must take care to ensure that the source is saved as UTF-8.
The same applies to Python 2, save that declaring the encoding is required if UTF-8 is to be used.
Having a reasonably comprehensive test suite would greatly reduce the risk of wrongly-encoded source files, as importing such a file will raise a SyntaxError. If the code lacks tests, it would not be difficult to write a script that searched for .py files, tried to open them specifying UTF-8 as the encoding, and reported any that raised UnicodeDecodeError

Python Notepad++ encoding error

I am using Python for the first time and am running into an encoding error that I can't seem to get around. Here is the code:
#!/usr/bin/python
#-*- coding: utf -*-
import pandas as pd
a = "C:\Users"
print(a)
When I do this, I get:
File "C:\Users\Public\Documents\Python Scripts\ImportExcel.py", line
5
a = "C:\Users"
^ SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in positio n 2-3: truncated \UXXXXXXXX escape
In Notepad++ I have tried all of the encoding options. Nothing seems to work.
Any suggestions?

Specifically, the problem is that the '\' is an escape character.
If you want to print the string
"C:\Users"
then you have to do it thus:
a = "C:\\Users"
Hope this helps.

The error message suggests you're on a Windows machine, but you're using *nix notation for #!/usr/bin/python. That line should look something like #!C:\Python33\python.exe on a Windows machine, depending on where you've installed Python.

Use this: # -*- coding: utf-8 -*- instead of #-- coding: utf --

You can set the encoding in Notepad++, but you also need to tell Python about it.
In legacy Python (2.7), source code is ASCII unless specified otherwise. In Python 3, source code is UTF-8 unless otherwise specified.
You should use the following as the first or second line of the file to specify the encoding of the source code. The documentation gives:
# -*- coding: <encoding> -*-
This is the format originally from the Emacs editor, but according to PEP263 you can also use:
# vim: set fileencoding=<encoding>:
of even:
# coding=<encoding>
Where <encoding> can be any encoding that Python supports, but utf-8 is generally a good choice for portable code.

Unicode with cp1251 and utf-8 on windows

I am playing around with unicode in python.
So there is a simple script:
# -*- coding: cp1251 -*-
print 'юникод'.decode('cp1251')
print unicode('юникод', 'cp1251')
print unicode('юникод', 'utf-8')
In cmd I've switched encoding to Active code page: 1251.
And there is the output:
СЋРЅРёРєРѕРґ
СЋРЅРёРєРѕРґ
юникод
I am a little bit confused.
Since I've specified encoding to cp1251 I expect that it would be decoded correctly.
But as result there is some trash code points were interpreted.
I am understand that 'юникод' is just a bytes like:
'\xd1\x8e\xd0\xbd\xd0\xb8\xd0\xba\xd0\xbe\xd0\xb4'.
But there is a way to get correct output in terminal with cp1251?
Should I build byte string manually?
Seems like I misunderstood something.

I think I can understand what happened to you. The last line gave me the hint, that your trash codepoints confirmed. You try to display cp1251 characters but your editor is configured to use utf8.
The # -*- coding: cp1251 -*- is only used by the Python interpretor to convert characters from source python files that are outside of the ASCII range. And anyway it it is only used for unicode litterals because bytes from original source give er... exactly same bytes in byte strings. Some text editors are kind enough to automagically use this line (IDLE editor is), but I'm little confident in that and allways switch manually to the proper encoding when I use gvim for example. Short story: # -*- coding: cp1251 -*- in unused in your code and can only mislead a reader since it it not the actual encoding.
If you want to be sure of what lies in your source, you'd better use explicit escapes. In code page 1251, this word юникод is composed by those characters: '\xfe\xed\xe8\xea\xee\xe4'
If you write this source:
txt = '\xfe\xed\xe8\xea\xee\xe4'
print txt
print txt.decode('cp1251')
print unicode(txt, 'cp1251')
print unicode(txt, 'utf-8')
and execute it in a console configured to use CP1251 charset, the first three lines will output юникод, and the last one will throw a UnicodeDecodeError exception because the input is no longer valid 'utf8'.
Alternatively, if you find comfortable with you current editor, you could write:
# -*- coding: utf8 -*-
txt = 'юникод'.decode('utf8').encode('cp1251') # or simply txt = u'юникод'.encode('cp1251')
print txt
print txt.decode('cp1251')
print unicode(txt, 'cp1251')
print unicode(txt, 'utf-8')
which should give same results - but now the declared source encoding should be the actual encoding of your python source.
BTW, a Python 3.5 IDLE that natively uses unicode confirmed that:
>>> 'СЋРЅРёРєРѕРґ'.encode('cp1251').decode('utf8')
'юникод'

Your issue is that the encoding declaration is wrong: your editor uses utf-8 character encoding to save the source code. Use # -*- coding: utf-8 -*- to fix it.
>>> u'юникод'
u'\u044e\u043d\u0438\u043a\u043e\u0434'
>>> u'юникод'.encode('utf-8')
'\xd1\x8e\xd0\xbd\xd0\xb8\xd0\xba\xd0\xbe\xd0\xb4'
>>> print _.decode('cp1251') # mojibake due to the wrong encoding
СЋРЅРёРєРѕРґ
>>> print u'юникод'
юникод
Do not use bytestrings ('' literals create bytes object on Python 2) to represent text; use Unicode strings (u'' literals -- unicode type) instead.
If your code uses Unicode strings then a code page that your Windows console uses doesn't matter as long as the chosen font can display the corresponding (non-BMP) characters. See Python, Unicode, and the Windows console
Here's complete code, for reference:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
print(u'юникод')
Note: no .decode(), unicode(). If you are using a literal to create a string; you should use Unicode literals if the string contains text. It is the only option on Python 3 where you can't put non-ascii characters inside a bytes literal and it is a good practice (to use Unicode for text instead of bytestrings) on Python 2 too.
If you are given a bytestring as an input (not literal) by some API then its encoding has nothing to do with the encoding declaration. What specific encoding to use depends on the source of the data.

Just use the following, but ensure you save the source code in the declared encoding. It can be any encoding that supports the characters you want to print. The terminal can be in a different encoding, as long as it also supports the characters you want to print:
#coding:utf8
print u'юникод'
The advantage is that you don't need to know the terminal's encoding. Python will normally1 detect the terminal encoding and encode the print output correctly.
1Unless your terminal is misconfigured.

What is the default encoding method for code assumed by Python interpreter?

Some people use the following to declare the encoding method for the text of their Python source code:
# -*- coding: utf-8 -*-
Back in 2001, it is said the default encoding method that Python interpreter assumes is ASCII. I have dealt with strings using non-ASCII characters in my Python code, without declaring encoding method of my code, and I don't remember I have bumped into encoding error before. What is the default encoding for code assumed by Python interpreter now?
I am not sure if this is relevant.
My OS is Ubuntu, and I am using the default Python interpreter, and gedit or emacs for editing.
Will the default encoding method by Python interpreter changes if the above changes?
Thanks.

Without any explicit encoding declaration, the assumed encoding for your source code will be
ascii for Python 2.x
utf-8 for Python 3.x
See PEP 0263 and Using source code encoding for Python 2.x, and PEP 3120 for the new default of utf-8 for Python 3.x.
So the default encoding assumened for source code will be directly dependent of the version of the Python interpreter, and it is not configurable.
Note that the source code encoding is something entirely different than dealing with non-ASCII characters as part of your data in strings.
There are two distinct cases where you may encounter non-ASCII characters:
As part of your programs data, during runtime
As part of your source code (and since you can't have non-ASCII characters in identifiers, that usually means hard coded string data in your source code or comments).
The source code encoding declaration affects what encoding your source code will be interpreted with - so it's only needed if you decide to directly put non-ASCII characters in your source code.
So, the following code will eventually have to deal with the fact that there might be non-ASCII characters in data.txt:
with open('data.txt') as f:
for line in f:
# do something with `line`
But it doesn't contain any non-ASCII characters in the source code, therefore it doesn't need an encoding declaration at the top of the file. It will however need to properly decode line if it wants to turn it into unicode. Simply doing unicode(line) will use the system default encoding, which is ascii (different from the default source encoding, but happens to also be ascii). So to explicitely decode the string using utf-8 you'd need to do line.decode('utf-8').
This code however does contain non-ASCII characters directly in its source code:
TEST_DATA = 'Bär' # <--- non-ASCII character on this line
print TEST_DATA
And it will fail with a SyntaxError similar to this, unless you declare an explicit source code encoding:
SyntaxError: Non-ASCII character '\xc3' in file foo.py on line 1, but no encoding declared;
see http://www.python.org/peps/pep-0263.html for details
So assuming your text editor is configured to save files in utf-8, you'd need to put the line
# -*- coding: utf-8 -*-
at the top of the file for Python to interpret the source code correctly.
My advice however would be to generally avoid putting non-ASCII characters in your source code, exactly because if it depends on your and your co-workers editor and terminal settings wheter it will be written and read correctly.
Instead you can use escaped strings to safely enter non-ASCII characters in your code:
TEST_DATA = 'B\xc3\xa4r'

By default, Python source files are treated as encoded in UTF-8. In that encoding, — although the standard library only uses ASCII characters for identifiers, a convention that any portable code should follow. To display all these characters properly, the editor must recognize that the file is UTF-8, and it must use a font that supports all the characters in the file.
It is also possible to specify a different encoding for source files. In order to do this, we put the below code on top of our code !
# -*- coding: encoding -*-
https://docs.python.org/dev/tutorial/interpreter.html

A source file with unicode characters is making Django throw up a SyntaxError exception

A file in UTF-8 encoding has an è character (e with accent grave) embedded in comment delimiters for Python. Django complains about this character and will not render the page. How can I resolve this?

The SyntaxError Django is raising already points you in the right direction.
It is always a good thing to actually read exceptions. In your case, it will have said something along the lines of
Non-ASCII character '\xc3' in file /home/zakx/../views.py on line 84, but no encoding declared; see http://www.python.org/peps/pep-0263.html for details (views.py, line 84)
If you'd then read PEP-0263, you could learn that there are some ways to tell Python (and your editor!) which encoding your files are in. Generally, you will want to use UTF-8 encoding whenever possible. Therefore, writing one of the following lines into the first line (or second, if you use a shebang) will tell Python to use UTF-8 for that file.
# coding=utf8
# -*- coding: utf8 -*-
# vim: set fileencoding=utf8 :

Did you try adding the coding header to the file? On the first line, possibly after the shebang line, add
# -*- coding: utf-8 -*-