How can I capture return value with Python timeit module?

For Python 3.5 you can override the value of timeit.template

timeit.template = """
def inner(_it, _timer{init}):
    {setup}
    _t0 = _timer()
    for _i in _it:
        retval = {stmt}
    _t1 = _timer()
    return _t1 - _t0, retval
"""

unutbu's answer works for python 3.4 but not 3.5 as the _template_func function appears to have been removed in 3.5

The problem boils down to timeit._template_func not returning the function's return value:

def _template_func(setup, func):
    """Create a timer function. Used if the "statement" is a callable."""
    def inner(_it, _timer, _func=func):
        setup()
        _t0 = _timer()
        for _i in _it:
            _func()
        _t1 = _timer()
        return _t1 - _t0
    return inner

We can bend timeit to our will with a bit of monkey-patching:

import timeit
import time

def _template_func(setup, func):
    """Create a timer function. Used if the "statement" is a callable."""
    def inner(_it, _timer, _func=func):
        setup()
        _t0 = _timer()
        for _i in _it:
            retval = _func()
        _t1 = _timer()
        return _t1 - _t0, retval
    return inner

timeit._template_func = _template_func

def foo():
    time.sleep(1)
    return 42

t = timeit.Timer(foo)
print(t.timeit(number=1))

returns

(1.0010340213775635, 42)

The first value is the timeit result (in seconds), the second value is the function's return value.

Note that the monkey-patch above only affects the behavior of timeit when a callable is passed timeit.Timer. If you pass a string statement, then you'd have to (similarly) monkey-patch the timeit.template string.