Issue with python mode in 24.5 on Mac OSX Yosemite: python-rx missing?

Question

I installed Emacs 24.5 using homebrew

$ brew install emacs

and the Emacs-Live package collection. Most things work really well, but I'd like to get a python IDE going in emacs (so I don't have to leave emacs to run python, etc.)

First, I open up one of my python programs, foo.py:

print 42

and verify this works from the shell:

M-xshell

$ python foo.py
42

Great. The underpinnings seem to be working.

Following the minor-mode help (M-x helpm), which shows many key bindings, I now start the python subprocess:

C-cC-p

 Python 2.7.10 (default, Jun 10 2015, 19:42:47) 
 [GCC 4.2.1 Compatible Apple LLVM 6.1.0 (clang-602.0.53)] on darwin
 Type "help", "copyright", "credits" or "license" for more information.
 >>> 

Now I try to send my program to this subprocess:

C-cC-c

Wrong type argument: stringp, nil

Uh-oh. Ok, I can deal with this. Back to *Help* mode. M-xhelp, find the entry for C-cC-c

C-c C-c      python-shell-send-buffer <<<--- that's a hyperlink

clink on the hyperlink:

python-shell-send-buffer is an interactive compiled Lisp function in
`python.el'.  <<<--- that's a hyperlink

click on that hyperlink:

(defun python-shell-send-buffer (&optional send-main)
  "Send the entire buffer to inferior Python process.
When optional argument SEND-MAIN is non-nil, allow execution of
...etc...

put the point cursor in the defun and press C-uC-M-x, which instruments the function for Edebug. Another C-cC-c in my python buffer and Edebug stops in this function. Info-mode has full documentation of Edebug,

M-xinfoRet mm ElispRet mm DebuggingRet mm EdebugRet

and I do lots of stepping into and checking stuff, which I won't repeat here. Suffice to say, I eventually find the offending line inside python.el, line 4138

(set (make-local-variable 'outline-regexp)
       (python-rx (* space) block-start))

When I try to step into this call of python-rx, Edebug either tells me that it can't find function python-rx,

Symbol's function definition is void: python-rx

or emacs goes into the weeds and I have to Force-Kill it, depending on how much other stuff I've done in the debugger session. I try looking for python-rx

M-x find-grep-dired

/usr/local/Cellar/emacs/24.5/share/emacs/24.5/lisp/progmodes

(I think this is where homebrew puts emacs lisp code for program modes)

python-rx

nothing found :(

I find it hard to believe that python mode is actually broken in this distro -- millions would have picked up their pitchforks and torches and taken to the streets. It must be something I've done wrong. I'd be grateful for any advice.