results

Williams-MacBook-Pro-2:tmp bdbaddog$ python bill_try_dict_keyerror.py
hiit:   0.04
hii :   0.03
nit :   0.82
nii :   0.07
Williams-MacBook-Pro-2:tmp bdbaddog$ python3.7 bill_try_dict_keyerror.py
hiit:   0.04
hii :   0.03
nit :   0.41
nii :   0.03
Williams-MacBook-Pro-2:tmp bdbaddog$ python3.6 bill_try_dict_keyerror.py
hiit:   0.03
hii :   0.03
nit :   0.41
nii :   0.04
Williams-MacBook-Pro-2:tmp bdbaddog$ python3.5 bill_try_dict_keyerror.py
hiit:   0.03
hii :   0.03
nit :   0.31
nii :   0.03

try vs in dict contents

from __future__ import print_function

import timeit

setup="""\
test_dict= {'haveit':99}
"""

hasit_try = """\
try:
    test_dict['haveit']
except KeyError:
    pass
"""

notit_try = """\
try:
    test_dict['donthaveit']
except KeyError:
    pass
"""

hasit_in = """\
if 'haveit' not in test_dict:
    pass
"""

notit_in = """\
if 'xhaveit' not in test_dict:
    pass
"""


hitt = timeit.timeit(stmt=hasit_try, setup=setup)
hii = timeit.timeit(stmt=hasit_in, setup=setup)
nit = timeit.timeit(stmt=notit_try, setup=setup)
nii = timeit.timeit(stmt=notit_in, setup=setup)

print("hiit: %6.2f"%hitt)
print("hii : %6.2f"%hii)
print("nit : %6.2f"%nit)
print("nii : %6.2f"%nii)