Retrospect

Dynamic logging after the fact

Classic logging expects perfect foresight, but only hindsight is 20/20!

Usage

Install via pip, then enter in a shell:

def hello(a, b=2):
    """docstring"""
    a = 1
    c = b * 2
    a = b = c = a * 2 + b * c
    print('output: a={} b={} c={}'.format(a, b, c))
    return a, b, c

import retrospect
retro = retrospect.FunctionRetrospector(hello)

Now you can start inspecting lines in real-time:

>>> retro.implement(lines=True)
>>> hello(10)
((3, SetLineno, 3), {'a': 10, 'b': 2})
((4, SetLineno, 4), {'a': 1, 'b': 2})
((5, SetLineno, 5), {'a': 1, 'b': 2, 'c': 4})
((6, SetLineno, 6), {'a': 10, 'b': 10, 'c': 10})
output: a=10 b=10 c=10
((7, SetLineno, 7), {'a': 10, 'b': 10, 'c': 10})
((7, RETURN_VALUE, None), {'a': 10, 'b': 10, 'c': 10})

Or a specific set of lines:

>>> retro.implement(lines=[4], boundaries=False)
>>> hello(20)
((4, SetLineno, 4), {'a': 1, 'b': 2})
output: a=10 b=10 c=10

Or only on symbol changes:

>>> retro.implement(symbols=True, boundaries='start')
>>> hello(30)
((3, SetLineno, 3), {'a': 30, 'b': 2})
((3, STORE_FAST, 'a'), {'a': 30, 'b': 2})
((3, STORE_FAST, 'a'), {'a': 1, 'b': 2})
((4, STORE_FAST, 'c'), {'a': 1, 'b': 2})
((4, STORE_FAST, 'c'), {'a': 1, 'b': 2, 'c': 4})
((5, STORE_FAST, 'a'), {'a': 1, 'b': 2, 'c': 4})
((5, STORE_FAST, 'a'), {'a': 10, 'b': 2, 'c': 4})
((5, STORE_FAST, 'b'), {'a': 10, 'b': 2, 'c': 4})
((5, STORE_FAST, 'b'), {'a': 10, 'b': 10, 'c': 4})
((5, STORE_FAST, 'c'), {'a': 10, 'b': 10, 'c': 4})
((5, STORE_FAST, 'c'), {'a': 10, 'b': 10, 'c': 10})
output: a=10 b=10 c=10

Or specific opcodes:

>>> retro.implement(opcodes=['LOAD_CONST'], boundaries='finish')
>>> hello(40)
((3, LOAD_CONST, 1), {'a': 40, 'b': 2})
((4, LOAD_CONST, 2), {'a': 1, 'b': 2})
((5, LOAD_CONST, 2), {'a': 1, 'b': 2, 'c': 4})
((6, LOAD_CONST, 'output: a={} b={} c={}'), {'a': 10, 'b': 10, 'c': 10})
output: a=10 b=10 c=10
((7, RETURN_VALUE, None), {'a': 10, 'b': 10, 'c': 10})

Or return to exact original:

>>> retro.implement()
>>> hello(50)
output: a=10 b=10 c=10

Any of the above can be mixed as necessary, eg. lines=True, symbols="c"