Hi folks, 

While going about running tkinter's update() call within a coroutine/asyncio event loop in lieu of using mainloop(), I came across odd memory behavior on MacOS where the cpython process gradually increases memory consumption. Suspicious that there may be some unfavorable interaction between asyncio's use of KqueueSelector and the lower level tk calls, I stripped things down to a simple implementation and found the behavior exhibits itself without asyncio involved at all. 

```
import tkinter as tk


def start(root):

    while True:
        root.update()


# tk update loop: mem consumption increases
start(tk.Tk())

# tk mainloop: mem consumption stable
# tk.Tk().mainloop()
```

# Using tk mainloop, ~1 minute
/Users/jeremy$ /usr/bin/time -l python3.5 tk_perf.py
       60.26 real         0.16 user         0.07 sys
  31756288  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
     10215  page reclaims
         0  page faults
         0  swaps
         0  block input operations
         7  block output operations
         0  messages sent
         0  messages received
         0  signals received
         7  voluntary context switches
      1788  involuntary context switches

# tk update loop, ~1 minute
/Users/jeremy$ /usr/bin/time -l python3.5 tk_perf.py
Traceback (most recent call last):
  File "tk_perf.py", line 10, in <module>
    start(tk.Tk())
  File "tk_perf.py", line 7, in start
    root.update()
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/tkinter/__init__.py", line 1025, in update
    self.tk.call('update')
_tkinter.TclError: can't invoke "update" command:  application has been destroyed
       60.37 real        38.09 user        20.54 sys
 545976320  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
    135760  page reclaims
         2  page faults
         0  swaps
         0  block input operations
         9  block output operations
         0  messages sent
         0  messages received
         0  signals received
    474742  voluntary context switches
   1672276  involuntary context switches

That's 31,756,288 versus 545,976,320 after ~1 minute. If I let the update loop continue, it eventually consumes many gigabytes of memory. 

Obviously something is very wrong here. To further the fun, I've tested this across three Macs, and only two exhibit the behavior. This may or may not be interesting to those who are already aware of Tk / Cocoa event loop interaction issues.

+---------------+----------------+----------------+----------+
| MacOS Version | Python Version | Tcl/Tk Version | Exhibits |
+---------------+----------------+----------------+----------+
| 10.11.3/15D21 | 3.5.1          | 8.5/8.5        | Yes      |
| 10.9.4/13E28  | 3.5.1          | 8.5/8.5        | No       |
| 10.11.2/15C50 | 3.5.1          | 8.5/8.5        | Yes      |
+---------------+----------------+----------------+----------+

Could someone illuminate me as to as whether I'm facing a PEBKAC, update() is lacking some housekeeping that exists in the mainloop routine, a new/known bug, or other? Further troubleshooting steps I can take are appreciated, I'm happy to try to isolate it further. 

My use case is a tkinter app written solely w/ coroutines thus the event loop selection is constrained.

Env details below.. Cheers.



~~~ENV~~~~


/Users/jeremy$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.11.3
BuildVersion:	15D21

/Users/jeremy$ python3.5 --version
Python 3.5.1

>>> import _tkinter
>>> _tkinter.__spec__
ModuleSpec(name='_tkinter', loader=<_frozen_importlib_external.ExtensionFileLoader object at 0x1028ae5c0>, origin='/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/lib-dynload/_tkinter.cpython-35m-darwin.so')
>>> _tkinter.TCL_VERSION, _tkinter.TK_VERSION
('8.5', '8.5')


/Users/jeremy$ python3.5 -m sysconfig "sysconfig.get_config_vars()"
Platform: "macosx-10.11-x86_64"
Python version: "3.5"
Current installation scheme: "posix_prefix"

Paths:
	data = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	include = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include/python3.5m"
	platinclude = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include/python3.5m"
	platlib = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages"
	platstdlib = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5"
	purelib = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages"
	scripts = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/bin"
	stdlib = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5"

Variables:
	ABIFLAGS = "m"
	AC_APPLE_UNIVERSAL_BUILD = "0"
	AIX_GENUINE_CPLUSPLUS = "0"
	AR = "ar"
	ARFLAGS = "rc"
	ASDLGEN = "python ./Parser/asdl_c.py"
	ASDLGEN_FILES = "./Parser/asdl.py ./Parser/asdl_c.py"
	AST_ASDL = "./Parser/Python.asdl"
	AST_C = "Python/Python-ast.c"
	AST_C_DIR = "Python"
	AST_H = "Include/Python-ast.h"
	AST_H_DIR = "Include"
	BASECFLAGS = "-Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic"
	BASECPPFLAGS = ""
	BASEMODLIBS = ""
	BINDIR = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/bin"
	BINLIBDEST = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5"
	BLDLIBRARY = ""
	BLDSHARED = "clang -bundle -undefined dynamic_lookup"
	BUILDEXE = ".exe"
	BUILDPYTHON = "python.exe"
	BUILD_GNU_TYPE = "x86_64-apple-darwin15.4.0"
	BYTESTR_DEPS = "\"
	CC = "clang"
	CCSHARED = ""
	CFLAGS = "-Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes"
	CFLAGSFORSHARED = ""
	CFLAGS_NODIST = ""
	CONFIGFILES = "configure configure.ac acconfig.h pyconfig.h.in Makefile.pre.in"
	CONFIGURE_CFLAGS = ""
	CONFIGURE_CFLAGS_NODIST = "-Werror=declaration-after-statement"
	CONFIGURE_CPPFLAGS = ""
	CONFIGURE_LDFLAGS = ""
	CONFIG_ARGS = "'--prefix=/usr/local/Cellar/python3/3.5.1' '--enable-ipv6' '--datarootdir=/usr/local/Cellar/python3/3.5.1/share' '--datadir=/usr/local/Cellar/python3/3.5.1/share' '--enable-framework=/usr/local/Cellar/python3/3.5.1/Frameworks' '--without-ensurepip' '--without-gcc' 'MACOSX_DEPLOYMENT_TARGET=10.11' 'CC=clang' 'PKG_CONFIG_PATH=/usr/local/opt/xz/lib/pkgconfig:/usr/local/opt/sqlite/lib/pkgconfig:/usr/local/opt/openssl/lib/pkgconfig' 'PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig:/usr/local/Library/ENV/pkgconfig/10.11'"
	CONFINCLUDEDIR = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include"
	CONFINCLUDEPY = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include/python3.5m"
	COREPYTHONPATH = ":plat-darwin"
	COVERAGE_INFO = "/private/tmp/python320160418-12904-1t6reri/Python-3.5.1/coverage.info"
	COVERAGE_REPORT = "/private/tmp/python320160418-12904-1t6reri/Python-3.5.1/lcov-report"
	COVERAGE_REPORT_OPTIONS = "--no-branch-coverage --title "CPython lcov report""
	CPPFLAGS = "-I. -IInclude -I./Include"
	CXX = "clang++"
	DESTDIRS = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5 /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5 /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/lib-dynload"
	DESTLIB = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5"
	DESTPATH = ""
	DESTSHARED = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/lib-dynload"
	DIRMODE = "755"
	DIST = "README ChangeLog configure configure.ac acconfig.h pyconfig.h.in Makefile.pre.in Include Lib Misc Ext-dummy"
	DISTDIRS = "Include Lib Misc Ext-dummy"
	DISTFILES = "README ChangeLog configure configure.ac acconfig.h pyconfig.h.in Makefile.pre.in"
	DLINCLDIR = "."
	DLLLIBRARY = ""
	DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754 = "0"
	DOUBLE_IS_BIG_ENDIAN_IEEE754 = "0"
	DOUBLE_IS_LITTLE_ENDIAN_IEEE754 = "1"
	DYNLOADFILE = "dynload_shlib.o"
	ENABLE_IPV6 = "1"
	ENSUREPIP = "no"
	EXE = ""
	EXEMODE = "755"
	EXTRAMACHDEPPATH = ""
	EXTRATESTOPTS = ""
	EXTRA_CFLAGS = ""
	EXT_SUFFIX = ".cpython-35m-darwin.so"
	FILEMODE = "644"
	FLOCK_NEEDS_LIBBSD = "0"
	GETPGRP_HAVE_ARG = "0"
	GETTIMEOFDAY_NO_TZ = "0"
	GNULD = "no"
	GRAMMAR_C = "Python/graminit.c"
	GRAMMAR_H = "Include/graminit.h"
	GRAMMAR_INPUT = "./Grammar/Grammar"
	HAVE_ACCEPT4 = "0"
	HAVE_ACOSH = "1"
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	HAVE_UINTPTR_T = "1"
	HAVE_UNAME = "1"
	HAVE_UNISTD_H = "1"
	HAVE_UNLINKAT = "1"
	HAVE_UNSETENV = "1"
	HAVE_USABLE_WCHAR_T = "0"
	HAVE_UTIL_H = "1"
	HAVE_UTIMENSAT = "0"
	HAVE_UTIMES = "1"
	HAVE_UTIME_H = "1"
	HAVE_WAIT3 = "1"
	HAVE_WAIT4 = "1"
	HAVE_WAITID = "1"
	HAVE_WAITPID = "1"
	HAVE_WCHAR_H = "1"
	HAVE_WCSCOLL = "1"
	HAVE_WCSFTIME = "1"
	HAVE_WCSXFRM = "1"
	HAVE_WMEMCMP = "1"
	HAVE_WORKING_TZSET = "1"
	HAVE_WRITEV = "1"
	HAVE_ZLIB_COPY = "1"
	HAVE__GETPTY = "0"
	HGBRANCH = ""
	HGTAG = ""
	HGVERSION = ""
	HOST_GNU_TYPE = "x86_64-apple-darwin15.4.0"
	INCLDIRSTOMAKE = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include/python3.5m /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include/python3.5m"
	INCLUDEDIR = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include"
	INCLUDEPY = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/include/python3.5m"
	INSTALL = "/usr/bin/install -c"
	INSTALL_DATA = "/usr/bin/install -c -m 644"
	INSTALL_PROGRAM = "/usr/bin/install -c"
	INSTALL_SCRIPT = "/usr/bin/install -c"
	INSTALL_SHARED = "/usr/bin/install -c -m 555"
	INSTSONAME = "Python.framework/Versions/3.5/Python"
	IO_H = "Modules/_io/_iomodule.h"
	IO_OBJS = "\"
	LDCXXSHARED = "clang++ -bundle -undefined dynamic_lookup"
	LDFLAGS = ""
	LDLAST = ""
	LDLIBRARY = "Python.framework/Versions/3.5/Python"
	LDLIBRARYDIR = ""
	LDSHARED = "clang -bundle -undefined dynamic_lookup"
	LDVERSION = "3.5m"
	LIBC = ""
	LIBDEST = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5"
	LIBDIR = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib"
	LIBFFI_INCLUDEDIR = ""
	LIBM = ""
	LIBOBJDIR = "Python/"
	LIBOBJS = ""
	LIBPC = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/pkgconfig"
	LIBPL = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/config-3.5m"
	LIBRARY = "libpython3.5m.a"
	LIBRARY_OBJS = "\"
	LIBRARY_OBJS_OMIT_FROZEN = "\"
	LIBS = "-ldl  -framework CoreFoundation"
	LIBSUBDIRS = "tkinter tkinter/test tkinter/test/test_tkinter \"
	LINKCC = "clang"
	LINKFORSHARED = "-Wl,-stack_size,1000000  -framework CoreFoundation Python.framework/Versions/3.5/Python"
	LIPO_32BIT_FLAGS = ""
	LLVM_PROF_ERR = "yes"
	LLVM_PROF_FILE = "LLVM_PROFILE_FILE="code-%p.profclangr""
	LLVM_PROF_MERGER = "llvm-profdata merge -output=code.profclangd *.profclangr"
	LN = "ln"
	LOCALMODLIBS = ""
	LOG1P_DROPS_ZERO_SIGN = "0"
	MACHDEP = "darwin"
	MACHDEPPATH = ":plat-darwin"
	MACHDEPS = "plat-darwin"
	MACHDEP_OBJS = ""
	MACHDESTLIB = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5"
	MACOSX_DEPLOYMENT_TARGET = "10.11"
	MAINCC = "clang"
	MAJOR_IN_MKDEV = "0"
	MAJOR_IN_SYSMACROS = "0"
	MAKESETUP = "./Modules/makesetup"
	MANDIR = "/usr/local/Cellar/python3/3.5.1/share/man"
	MKDIR_P = "./install-sh -c -d"
	MODLIBS = ""
	MODOBJS = "Modules/_threadmodule.o  Modules/signalmodule.o  Modules/posixmodule.o  Modules/errnomodule.o  Modules/pwdmodule.o  Modules/_sre.o  Modules/_codecsmodule.o  Modules/_weakref.o  Modules/_functoolsmodule.o  Modules/_operator.o  Modules/_collectionsmodule.o  Modules/itertoolsmodule.o  Modules/atexitmodule.o  Modules/_stat.o  Modules/timemodule.o  Modules/_localemodule.o  Modules/_iomodule.o Modules/iobase.o Modules/fileio.o Modules/bytesio.o Modules/bufferedio.o Modules/textio.o Modules/stringio.o  Modules/zipimport.o  Modules/faulthandler.o  Modules/_tracemalloc.o Modules/hashtable.o  Modules/symtablemodule.o  Modules/xxsubtype.o"
	MODULE_OBJS = "\"
	MULTIARCH = ""
	MVWDELCH_IS_EXPRESSION = "1"
	NO_AS_NEEDED = ""
	OBJECT_OBJS = "\"
	OPCODETARGETGEN = "\"
	OPCODETARGETGEN_FILES = "\"
	OPCODETARGETS_H = "\"
	OPCODE_H = "./Include/opcode.h"
	OPCODE_H_DIR = "./Include"
	OPCODE_H_GEN = "python  ./Tools/scripts/generate_opcode_h.py ./Lib/opcode.py ./Include/opcode.h"
	OPCODE_H_SCRIPT = "./Tools/scripts/generate_opcode_h.py"
	OPT = "-DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes"
	OTHER_LIBTOOL_OPT = ""
	PACKAGE_BUGREPORT = "0"
	PACKAGE_NAME = "0"
	PACKAGE_STRING = "0"
	PACKAGE_TARNAME = "0"
	PACKAGE_URL = "0"
	PACKAGE_VERSION = "0"
	PARSER_HEADERS = "\"
	PARSER_OBJS = "\ Parser/myreadline.o Parser/parsetok.o Parser/tokenizer.o"
	PGEN = "Parser/pgen"
	PGENOBJS = "\ \"
	PGENSRCS = "\ \"
	PGOBJS = "\"
	PGO_PROF_GEN_FLAG = "-fprofile-instr-generate"
	PGO_PROF_USE_FLAG = "-fprofile-instr-use=code.profclangd"
	PGSRCS = "\"
	PLATDIR = "plat-darwin"
	POBJS = "\"
	POSIX_SEMAPHORES_NOT_ENABLED = "0"
	PROFILE_TASK = "-m test.regrtest --pgo"
	PSRCS = "\"
	PTHREAD_SYSTEM_SCHED_SUPPORTED = "1"
	PURIFY = ""
	PY3LIBRARY = ""
	PYLONG_BITS_IN_DIGIT = "0"
	PYTHON = "python"
	PYTHONFRAMEWORK = "Python"
	PYTHONFRAMEWORKDIR = "Python.framework"
	PYTHONFRAMEWORKINSTALLDIR = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework"
	PYTHONFRAMEWORKPREFIX = "/usr/local/Cellar/python3/3.5.1/Frameworks"
	PYTHONPATH = ":plat-darwin"
	PYTHON_FOR_BUILD = "./python.exe -E"
	PYTHON_HEADERS = "\"
	PYTHON_OBJS = "\"
	PY_CFLAGS = "-Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes"
	PY_CFLAGS_NODIST = "-Werror=declaration-after-statement"
	PY_CORE_CFLAGS = "-Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -Werror=declaration-after-statement -I. -IInclude -I./Include  -DPy_BUILD_CORE"
	PY_CPPFLAGS = "-I. -IInclude -I./Include"
	PY_FORMAT_LONG_LONG = ""ll""
	PY_FORMAT_SIZE_T = ""z""
	PY_LDFLAGS = ""
	Py_DEBUG = "0"
	Py_ENABLE_SHARED = "0"
	Py_HASH_ALGORITHM = "0"
	QUICKTESTOPTS = "-x test_subprocess test_io test_lib2to3 \"
	RANLIB = "ranlib"
	READELF = ":"
	RESSRCDIR = "Mac/Resources/framework"
	RETSIGTYPE = "void"
	RUNSHARED = "DYLD_FRAMEWORK_PATH=/private/tmp/python320160418-12904-1t6reri/Python-3.5.1"
	SCRIPTDIR = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib"
	SETPGRP_HAVE_ARG = "0"
	SGI_ABI = ""
	SHELL = "/bin/sh"
	SHLIBS = "-ldl  -framework CoreFoundation"
	SHLIB_SUFFIX = ".so"
	SIGNAL_OBJS = ""
	SIGNED_RIGHT_SHIFT_ZERO_FILLS = "0"
	SITEPATH = ""
	SIZEOF_DOUBLE = "8"
	SIZEOF_FLOAT = "4"
	SIZEOF_FPOS_T = "8"
	SIZEOF_INT = "4"
	SIZEOF_LONG = "8"
	SIZEOF_LONG_DOUBLE = "16"
	SIZEOF_LONG_LONG = "8"
	SIZEOF_OFF_T = "8"
	SIZEOF_PID_T = "4"
	SIZEOF_PTHREAD_T = "8"
	SIZEOF_SHORT = "2"
	SIZEOF_SIZE_T = "8"
	SIZEOF_TIME_T = "8"
	SIZEOF_UINTPTR_T = "8"
	SIZEOF_VOID_P = "8"
	SIZEOF_WCHAR_T = "4"
	SIZEOF__BOOL = "1"
	SO = ".cpython-35m-darwin.so"
	SOABI = "cpython-35m-darwin"
	SRCDIRS = "Parser Grammar Objects Python Modules Mac Programs"
	SRC_GDB_HOOKS = "./Tools/gdb/libpython.py"
	STDC_HEADERS = "1"
	STRICT_SYSV_CURSES = "/* Don't use ncurses extensions */"
	STRIPFLAG = "-s"
	SUBDIRS = ""
	SUBDIRSTOO = "Include Lib Misc"
	SYSLIBS = ""
	SYS_SELECT_WITH_SYS_TIME = "1"
	TANH_PRESERVES_ZERO_SIGN = "1"
	TCLTK_INCLUDES = ""
	TCLTK_LIBS = ""
	TESTOPTS = ""
	TESTPATH = ""
	TESTPYTHON = "DYLD_FRAMEWORK_PATH=/private/tmp/python320160418-12904-1t6reri/Python-3.5.1 ./python.exe"
	TESTPYTHONOPTS = ""
	TESTRUNNER = "DYLD_FRAMEWORK_PATH=/private/tmp/python320160418-12904-1t6reri/Python-3.5.1 ./python.exe ./Tools/scripts/run_tests.py"
	TESTTIMEOUT = "3600"
	THREADOBJ = "Python/thread.o"
	TIMEMODULE_LIB = "0"
	TIME_WITH_SYS_TIME = "1"
	TM_IN_SYS_TIME = "0"
	UNICODE_DEPS = "\"
	UNIVERSALSDK = ""
	USE_COMPUTED_GOTOS = "0"
	USE_INLINE = "1"
	VA_LIST_IS_ARRAY = "1"
	VERSION = "3.5"
	WANT_SIGFPE_HANDLER = "0"
	WINDOW_HAS_FLAGS = "0"
	WITH_DOC_STRINGS = "1"
	WITH_DYLD = "1"
	WITH_LIBINTL = "0"
	WITH_NEXT_FRAMEWORK = "1"
	WITH_PYMALLOC = "1"
	WITH_THREAD = "1"
	WITH_TSC = "0"
	WITH_VALGRIND = "0"
	X87_DOUBLE_ROUNDING = "0"
	XMLLIBSUBDIRS = "xml xml/dom xml/etree xml/parsers xml/sax"
	abiflags = "m"
	abs_builddir = "/private/tmp/python320160418-12904-1t6reri/Python-3.5.1"
	abs_srcdir = "/private/tmp/python320160418-12904-1t6reri/Python-3.5.1"
	base = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	datarootdir = "/usr/local/Cellar/python3/3.5.1/share"
	exec_prefix = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	installed_base = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	installed_platbase = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	platbase = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	prefix = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5"
	projectbase = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/bin"
	py_version = "3.5.1"
	py_version_nodot = "35"
	py_version_short = "3.5"
	srcdir = "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/config-3.5m"
	userbase = "/Users/jeremy/Library/Python/3.5"

You might want to try stripping it further, and see if you can reproduce it just using tk, without python involved.

That seems like a good idea, will do so and report back findings. Hey, good meeting you at PyCon, by the way. Met you at the freelance open space. :-)

Confirmed the problem is with Tk/MacOS. Running a simple TCL script yielded the same behavior in terms of memory. The hunt goes elsewhere... Thank you R. David for the suggestion. 

```
package require Tk

while 1 {
    update
}
```

# MacOS 10.9.4
/Users/jeremy$ /usr/bin/time -l tclsh update_loop.tcl
       60.20 real        34.67 user        21.42 sys
  18219008  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
      5836  page reclaims
        26  page faults
         0  swaps
         0  block input operations
         9  block output operations
         0  messages sent
         0  messages received
         0  signals received
    830419  voluntary context switches
   1663224  involuntary context switches

# MacOS 10.11.3
/Users/jeremy$ /usr/bin/time -l tclsh update_loop.tcl
       60.44 real        39.06 user        21.45 sys
 571715584  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
    141633  page reclaims
         0  page faults
         0  swaps
         0  block input operations
         3  block output operations
         0  messages sent
         0  messages received
         0  signals received
    521744  voluntary context switches
   1833399  involuntary context switches

Could you please file a report on Tk bugtracker?

https://core.tcl.tk/tk/ticket