How can you make python 2.x warn when coercing strings to unicode?

Question

A very common source of encoding errors is that python 2 will silently coerce strings to unicode when you add them together with unicode. This can

Answer 1

I did a little more research after asking this question and hit on the perfect answer. Armin Ronacher created a wonderful little tool called unicode-nazi. Just install it and run your program like this:

python -Werror -municodenazi myprog.py

and you get a traceback right where the coercion happened:

Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "SITE-PACKAGES/unicodenazi.py", line 128, in 
    main()
  File "SITE-PACKAGES/unicodenazi.py", line 119, in main
    execfile(sys.argv[0], main_mod.__dict__)
  File "myprog.py", line 4, in 
    print foo()
  File "myprog.py", line 2, in foo
    return 'bar' + u'baz'
  File "SITE-PACKAGES/unicodenazi.py", line 34, in warning_decode
    stacklevel=2)
UnicodeWarning: Implicit conversion of str to unicode

---

If you're dealing with python libraries that trigger implicit coercions themselves and you can't catch the exceptions or otherwise work around them, you can leave out the -Werror:

python -municodenazi myprog.py

and at least see a warning printed out on stderr when it happens:

/SITE-PACKAGES/unicodenazi.py:119: UnicodeWarning: Implicit conversion of str to unicode
  execfile(sys.argv[0], main_mod.__dict__)
barbaz