Debugging in Python 3.6: Better, Faster, Stronger

Transcription

1 Debugging in Python 3.6: Better, Faster, Stronger Elizaveta Shashkova JetBrains EuroPython 2017

2 Bio Software developer of PyCharm IDE at JetBrains Debugger Saint Petersburg, Russia 2

3 Debugging Adding print statements Logging 3

4 Debugging Adding print statements Logging Special tools: debuggers 4

5 Debugger s Performance Debuggers are 30 times slower Run Debug 5

6 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 6

7 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 7

8 Tracing Function sys.settrace(tracefunc) - set system tracing function def tracefunc(frame, event, arg): print(frame.f_lineno, event) return tracefunc sys.settrace(tracefunc) 8

9 Tracing Function def foo(): friends = ["Bob", "Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 9

10 Tracing Function def foo(): friends = ["Bob", "Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 1 call 10

11 Tracing Function def foo(): friends = ["Bob", Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 1 call 2 line 11

12 Tracing Function def foo(): friends = ["Bob", "Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 1 call 2 line 3 line 4 line Hi Bob! 12

13 Tracing Function def foo(): friends = ["Bob", "Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 1 call 2 line 3 line 4 line Hi Bob! 3 line 4 line Hi Tom! 13

14 Tracing Function def foo(): friends = ["Bob", "Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 1 call 2 line 3 line 4 line Hi Bob! 3 line 4 line Hi Tom! 5 line 5 return 14

15 Build Python Debugger Breakpoints Stepping 15

16 Tracing Debugger Suspend program if breakpoint s line equals frame.f_lineno Handle events for stepping 16

17 Performance def foo(): friends = ["Bob", "Tom"] for f in friends: print("hi %s! % f) return len(friends) sys.settrace(tracefunc) foo() 1 call 2 line 3 line 4 line Hi Bob! 3 line 4 line Hi Tom! 5 line 5 return 17

18 Example def calculate(): sum = 0 for i in range(10 ** 7): sum += i return sum

19 Example def calculate(): sum = 0 for i in range(10 ** 7): sum += i return sum def tracefunc(frame, event, arg): return tracefunc 19

20 Performance Run 0,80 sec Tracing 6,85 sec Breakpoints 19,81 sec 20

21 Performance Run 0,80 sec Tracing 6,85 sec Breakpoints 19,81 sec 21

22 Performance Run 0,80 sec Tracing 6,85 sec Breakpoints 19,81 sec 22

23 Performance Run 0,80 sec Tracing 6,85 sec Breakpoints 19,81 sec ~ 25 times slower! 23

24 Problem Tracing call on every line 24

25 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 25

26 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 26

27 Python

28 Python 3.6 New frame evaluation API PEP

29 PEP 523 Handle evaluation of frames Add a new field to code objects 29

30 Frame Evaluation def frame_eval(frame, exc): func_name = frame.f_code.co_name line_number = frame.f_lineno print(line_number, func_name) return _PyEval_EvalFrameDefault(frame, exc)

31 Frame Evaluation def frame_eval(frame, exc): func_name = frame.f_code.co_name line_number = frame.f_lineno print(line_number, func_name) return _PyEval_EvalFrameDefault(frame, exc) f 31

32 Frame Evaluation def frame_eval(frame, exc): func_name = frame.f_code.co_name line_number = frame.f_lineno print(line_number, func_name) return _PyEval_EvalFrameDefault(frame, exc) f 32

33 Frame Evaluation def frame_eval(frame, exc): func_name = frame.f_code.co_name line_number = frame.f_lineno print(line_number, func_name) return _PyEval_EvalFrameDefault(frame, exc) f 33

34 Frame Evaluation def frame_eval(frame, exc): func_name = frame.f_code.co_name line_number = frame.f_lineno print(line_number, func_name) return _PyEval_EvalFrameDefault(frame, exc) f

35 Frame Evaluation def frame_eval(frame, exc): func_name = frame.f_code.co_name line_number = frame.f_lineno print(line_number, func_name) return _PyEval_EvalFrameDefault(frame, exc) def set_frame_eval(): state = PyThreadState_Get() state.interp.eval_frame = frame_eval 35

36 Example 1 2 def first(): second() def second(): third() def third(): pass set_frame_eval() first() 36

37 Example def first(): second() def second(): third() def third(): pass set_frame_eval() first() 1 first 4 second 7 third 37

38 Custom Frame Evaluation It works! Executed while entering a frame Access to frame and code object 38

39 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 39

40 Problem Tracing call on every line 40

41 Problem Tracing call on every line Remove the tracing function! 41

42 Replace tracing function with frame evaluation function 42

43 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 43

44 Build Python Debugger Breakpoints Stepping 44

45 Breakpoints Access to the whole code object 45

46 Breakpoints Access to the whole code object Insert breakpoint s code into frame s code 46

47 Breakpoints def maximum(a, b): if a > b: return a else: return b

48 Breakpoints def maximum(a, b): if a > b: return a # breakpoint else: return b

49 Breakpoints def maximum(a, b): if a > b: return a # breakpoint else: return b 6 7 breakpoint()

50 Breakpoints def maximum(a, b): if a > b: breakpoint() return a # breakpoint else: return b

51 Python Bytecode def maximum(a, b): if a > b: return a else: return b import dis dis.dis(maximum) 9 51

52 Python Bytecode def maximum(a, b): if a > b: return a else: return b import dis dis.dis(maximum) 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 52

53 Python Bytecode def maximum(a, b): if a > b: return a else: return b import dis dis.dis(maximum) 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 53

54 Python Bytecode def maximum(a, b): if a > b: return a else: return b import dis dis.dis(maximum) 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE f 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 54

55 Python Bytecode def maximum(a, b): if a > b: return a else: return b import dis dis.dis(maximum) 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 55

56 Python Bytecode def maximum(a, b): if a > b: return a else: return b import dis dis.dis(maximum) 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 56

57 Python Bytecode 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 57

58 Python Bytecode 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 58

59 Python Bytecode 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 59

60 Python Bytecode 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 60

61 Bytecode Modification 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) breakpoint() 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b) 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 61

62 Bytecode Modification Insert breakpoint s code Update arguments and offsets 62

63 Bytecode Modification Insert breakpoint s code Update arguments and offsets 200 lines in Python 63

64 Bytecode Modification 2 0 LOAD_FAST 0 (a) 2 LOAD_FAST 1 (b) 4 COMPARE_OP 4 (>) 6 POP_JUMP_IF_FALSE LOAD_FAST 0 (a) breakpoint() 10 RETURN_VALUE 5 >> 12 LOAD_FAST 1 (b)?! 14 RETURN_VALUE 16 LOAD_CONST 0 (None) 18 RETURN_VALUE 64

65 Breakpoint Bytecode def _stop_at_break(): # a lot of code here def breakpoint(): _stop_at_break() 0 LOAD_GLOBAL 0 2 CALL_FUNCTION 0 4 POP_TOP 6 LOAD_CONST 0 8 RETURN_VALUE 65

66 Build Python Debugger Breakpoints Stepping 66

67 Stepping Inserting temporary breakpoint on every line Use old tracing function 67

68 Frame evaluation debugger is ready! 68

69 Example def calculate(): sum = 0 for i in range(10 ** 7): sum += i return sum

70 Example 1 Run 0,80 sec Tracing 19,81 sec Frame evaluation 70

71 Example 1 Run 0,80 sec Tracing 19,81 sec Frame evaluation 0,81 sec 71

72 Example def foo(): pass def calculate(): sum = 0 for i in range(10 ** 7): foo() sum += i return sum 72

73 Example 2 Run 1,73 sec Tracing 43,58 sec Frame evaluation 37,41 sec 73

74 PEP 523 Handle evaluation of frames Add a new field to code objects 74

75 PEP 523 Expand PyCodeObject struct co_extra - scratch space for the code object Mark frames without breakpoints 75

76 Mark Frames def frame_eval(frame, exc): flag = _PyCode_GetExtra(frame.f_code, index) if flag == NO_BREAKS_IN_FRAME: return _PyEval_EvalFrameDefault(frame, exc) # check for breakpoints

77 Example 2 Run 1,73 sec Tracing 43,58 sec Frame evaluation 1,91 sec 77

78 PEP 523 Handle evaluation of frames Add a new field to code objects 78

79 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 79

80 Contents Tracing debugger Python 3.6 Frame evaluation debugger Results 80

81 Real Life Example 81

82 Real Life Example Included into PyCharm Works in production 82

83 PyCharm Tracing w/o Cython 11,59 sec Tracing with Cython 5,66 sec Frame evaluation 0,28 sec 83

84 Frame evaluation rocks! 84

85 Disadvantages More complicated Only with CPython Only with Python

86 Frame Evaluation Let s move to Python 3.6! 86

87 Frame Evaluation Let s move to Python 3.6! Let s find another use cases! 87

88 Use cases def maximum(a, b): if a > b: return a # breakpoint else: return b 6 7 breakpoint()

89 PEP 523 Pyjion project JIT for Python 89

90 Frame Evaluation Let s move to Python 3.6! Let s find another use cases! 90

91 Links Prototype: frame-eval PyCharm Community Edition source code bytesinsert on PyPi 91

92 Questions? Prototype: frame-eval PyCharm Community Edition source code bytesinsert on 92