How can I unit test that something behaves differently when Python is in optimised mode? -

python allows run script in "optimised mode" passing -o option. if save script "assert.py":

assert false print("hello") 

then these 2 invocations of python result in different output (one prints exception message , stack trace, while other says hello):

python -m assert python -o -m assert 

the author of python script can determine whether python in optimised mode checking value of global name __debug__. allows different things depending upon whether running in optimised mode or not.

suppose want 1 thing if python in optimised mode, , quite different thing if not. easy enough - can use if __debug__:. suppose want unit test behaviour in each case correct. how should go doing this?

it occurred me set value of __debug__, you're not allowed this:

>>> __debug__ = false   file "<stdin>", line 1 syntaxerror: assignment keyword >>> 

consider code:

assert 123  if __debug__:     do_something() 

optimized bytecode empty. assert , bare if __debug__ statements evaluated during bytecode compilation, not @ runtime. so, if succeed @ changing __debug__ (e.g. setattr(builtins, '__debug__', true)), still won't able execute code.

the way have run test suite twice, first without -o, -o. can automate part, don't have manually.

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for completeness:

$ python3 >>> dis.dis('assert 123')   1           0 load_const               0 (123)               3 pop_jump_if_true        12               6 load_global              0 (assertionerror)               9 raise_varargs            1         >>   12 load_const               1 (none)              15 return_value >>> dis.dis('if __debug__: do_something()')   1           0 load_name                0 (do_something)               3 call_function            0 (0 positional, 0 keyword pair)               6 pop_top               7 load_const               0 (none)              10 return_value 

$ python3 -o >>> dis.dis('assert 123')   1           0 load_const               0 (none)               3 return_value >>> dis.dis('if __debug__: do_something()')   1           0 load_const               0 (none)               3 return_value 

note bare if __debug__ statements optimized out. if use complex conditions, appear in bytecode:

$ python3 -o >>> dis.dis('if __debug__ , something_else: do_something()')   1           0 load_name                0 (__debug__)               3 pop_jump_if_false       22               6 load_name                1 (something_else)               9 pop_jump_if_false       22              12 load_name                2 (do_something)              15 call_function            0 (0 positional, 0 keyword pair)              18 pop_top              19 jump_forward             0 (to 22)         >>   22 load_const               0 (none)              25 return_value