Set encoding in Python 3 CGI scripts

Answering this for late-comers because I don’t think that the posted answers get to the root of the problem, which is the lack of locale environment variables in a CGI context. I’m using Python 3.2.

open() opens file objects in text (string) or binary (bytes) mode for reading and/or writing; in text mode the encoding used to encode strings written to the file, and decode bytes read from the file, may be specified in the call; if it isn’t then it is determined by locale.getpreferredencoding(), which on linux uses the encoding from your locale environment settings, which is normally utf-8 (from e.g. LANG=en_US.UTF-8)
```
>>> f = open('foo', 'w')         # open file for writing in text mode
>>> f.encoding
'UTF-8'                          # encoding is from the environment
>>> f.write('€')                 # write a Unicode string
1
>>> f.close()
>>> exit()
user@host:~$ hd foo
00000000  e2 82 ac      |...|    # data is UTF-8 encoded
```
sys.stdout is in fact a file opened for writing in text mode with an encoding based on locale.getpreferredencoding(); you can write strings to it just fine and they’ll be encoded to bytes based on sys.stdout’s encoding; print() by default writes to sys.stdout – print() itself has no encoding, rather it’s the file it writes to that has an encoding;
```
>>> sys.stdout.encoding
'UTF-8'                          # encoding is from the environment
>>> exit()
user@host:~$ python3 -c 'print("€")' > foo
user@host:~$ hd foo
00000000  e2 82 ac 0a   |....|   # data is UTF-8 encoded; \n is from print()
```
; you cannot write bytes to sys.stdout – use sys.stdout.buffer.write() for that; if you try to write bytes to sys.stdout using sys.stdout.write() then it will return an error, and if you try using print() then print() will simply turn the bytes object into a string object and an escape sequence like \xff will be treated as the four characters \, x, f, f
```
user@host:~$ python3 -c 'print(b"\xe2\xf82\xac")' > foo
user@host:~$ hd foo
00000000  62 27 5c 78 65 32 5c 78  66 38 32 5c 78 61 63 27  |b'\xe2\xf82\xac'|
00000010  0a                                                |.|
```
in a CGI script you need to write to sys.stdout and you can use print() to do it; but a CGI script process in Apache has no locale environment settings – they are not part of the CGI specification; therefore the sys.stdout encoding defaults to ANSI_X3.4-1968 – in other words, ASCII; if you try to print() a string that contain non-ASCII characters to sys.stdout you’ll get “UnicodeEncodeError: ‘ascii’ codec can’t encode character…: ordinal not in range(128)”
a simple solution is to pass the Apache process’s LANG environment variable through to the CGI script using Apache’s mod_env PassEnv command in the server or virtual host configuration: PassEnv LANG; on Debian/Ubuntu make sure that in /etc/apache2/envvars you have uncommented the line “. /etc/default/locale” so that Apache runs with the system default locale and not the C (Posix) locale (which is also ASCII encoding); the following CGI script should run without errors in Python 3.2:
```
#!/usr/bin/env python3
import sys
print('Content-Type: text/html; charset=utf-8')
print()
print('<html><body><pre>' + sys.stdout.encoding + '</pre>h€lló wörld<body></html>')
```

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