The Hidden Power of the Python Runtime

The Hidden Power of the Python Runtime Elizaveta Shashkova PyCon
US 2020 Online Edition

@lisa_shashkova About Me w 4PGUXBSF%FWFMPQFSBU+FU#SBJOT 1Z$IBSN*%& w 4U1FUFSTCVSH 3VTTJB w
!MJTB@TIBTILPWB !2

@lisa_shashkova !3 :PVBMSFBEZVTFJUFWFSZEBZ

@lisa_shashkova Test Frameworks w VOJUUFTU w QZUFTU !4

@lisa_shashkova AssertionError w VOJUUFTU w !5 Traceback (most recent call
last): File “/file.py”, line 8, in test_value assert a == 2, "Wrong value!" AssertionError: Wrong value!

@lisa_shashkova AssertionError w VOJUUFTU w QZUFTU !6 Traceback (most recent
call last): File “/file.py”, line 8, in test_value assert a == 2, "Wrong value!" AssertionError: Wrong value! E AssertionError: Wrong value! E assert 1 == 2

@lisa_shashkova Contents w 1ZUIPO3VOUJNF w (FUUJOH3VOUJNF*OGPSNBUJPO w %FWFMPQNFOU5PPMT !7

@lisa_shashkova !9 l&WFSZUIJOHJTBOPCKFDUJO1ZUIPOz

@lisa_shashkova Python Objects w $PSFUZQFT w OVNCFST TUSJOHT DPMMFDUJPOT w
1SPHSBNVOJUPCKFDUT w GVODUJPOT DMBTTFT NPEVMFT !10

@lisa_shashkova Created Explicitly a = 27 def get_answer(): return 42
class Person: def __init__(self, age): self.age = age !11

@lisa_shashkova Python Objects w $SFBUFEFYQMJDJUMZ w WBSJBCMFT GVODUJPOT DMBTTFT NPEVMFT
!12

@lisa_shashkova Python Objects w $SFBUFEFYQMJDJUMZ w WBSJBCMFT GVODUJPOT DMBTTFT NPEVMFT
w $SFBUFEJNQMJDJUMZ w stack frame DPEFPCKFDU !13

@lisa_shashkova Stack Frame w 3FQSFTFOUTBQSPHSBNTDPQF w *OGPSNBUJPOBCPVUFYFDVUJPOTUBUF w $PSSFTQPOEJOHDPEFPCKFDU w
-PDBMBOEHMPCBMWBSJBCMFT w 0UIFSEBUB !14

@lisa_shashkova Stack Frame !15 def foo(n): n = n -
1 return n def bar(k): res = foo(k) return res * 2 print(bar(1)) module bar() 1 2 3 4 5 6 7 8 9 10 11

@lisa_shashkova Stack Frame !16 module bar() foo() def foo(n): n
= n - 1 return n def bar(k): res = foo(k) return res * 2 print(bar(1)) 1 2 3 4 5 6 7 8 9 10 11 def foo(n): n = n - 1 return n def bar(k): res = foo(k) return res * 2 print(bar(1))

@lisa_shashkova Stack Frame !19 module bar() def foo(n): n =
n - 1 return n def bar(k): res = foo(k) return res * 2 print(bar(1)) 1 2 3 4 5 6 7 8 9 10 11 def foo(n): n = n - 1 return n def bar(k): res = foo(k) return res * 2 print(bar(1))

@lisa_shashkova Python Power w "WBJMBCMFPVUPGUIFCPY !20 module bar()

@lisa_shashkova Python Power w "WBJMBCMFPVUPGUIFCPY w 4UBDLGSBNFPCKFDUTBDDFTT !21 module bar()

@lisa_shashkova Python Stack Frame •sys._getframe([depth]) •depth OVNCFSPGDBMMTCFMPXUIFUPQ •DVSSFOUGSBNF !23

@lisa_shashkova Frame Object !24

@lisa_shashkova Frame Object: Variables !25 w -PDBMWBSJBCMFT • frame.f_locals

@lisa_shashkova Frame Object: Variables !26 w -PDBMWBSJBCMFT • frame.f_locals w
(MPCBMWBSJBCMFT • frame.f_globals

@lisa_shashkova Frame Object: Variables !27 w -PDBMWBSJBCMFT • frame.f_locals w
(MPCBMWBSJBCMFT • frame.f_globals • locals() & globals()

@lisa_shashkova Code Object !28 •frame.f_code -GSBNF`TBUUSJCVUF

@lisa_shashkova Code Object !29 w 3FQSFTFOUTBDIVOLPGFYFDVUBCMFDPEF

@lisa_shashkova Code Object !30 w 3FQSFTFOUTBDIVOLPGFYFDVUBCMFDPEF >>> c = compile('a
+ b', 'a.py', 'eval') <code object <module> at 0x104f8fc90, file "a.py", line 1>

@lisa_shashkova Code Object !31 w 3FQSFTFOUTBDIVOLPGFYFDVUBCMFDPEF >>> c = compile('a
+ b', 'a.py', 'eval') <code object <module> at 0x104f8fc90, file "a.py", line 1> >>> eval(c, {'a': 1, 'b': 2}) 3

@lisa_shashkova Code Object !32 •code.co_filename pMFOBNFXIFSFJUXBTDSFBUFE •code.co_nameOBNFPGGVODUJPOPSNPEVMF •code.co_varnames OBNFTPGWBSJBCMFT

@lisa_shashkova Code Object !33 •code.co_filename pMFOBNFXIFSFJUXBTDSFBUFE •code.co_nameOBNFPGGVODUJPOPSNPEVMF •code.co_varnames OBNFTPGWBSJBCMFT •code.co_code
DPNQJMFECZUFDPEF EJTBTTFNCMFXJUIdis.dis()

@lisa_shashkova Frame Object !34 •frame.f_lineno -DVSSFOUMJOFOVNCFS •frame.f_trace -USBDJOHGVODUJPO •frame.f_back -
QSFWJPVTGSBNF

@lisa_shashkova Previous Frame !35 module bar() foo()

@lisa_shashkova Previous Frame !36 Traceback (most recent call last): File
"file.py", line 12, in <module> print(bar(1)) File "file.py", line 8, in bar res = foo(k) File "file.py", line 2, in foo raise ValueError("Wrong value!") ValueError: Wrong value! module bar() foo()

@lisa_shashkova Frame Object !37 w inspectNPEVMF

@lisa_shashkova Frame Object !38 w inspectNPEVMF w )BOEMFGSBNFWBSJBCMFDBSFGVMMZ def handle_stackframe_without_leak():
frame = inspect.currentframe() try: # do something with the frame finally: del frame

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest !41

@lisa_shashkova Exception Object w tb = e.__traceback__USBDFCBDLPCKFDU w tb.tb_frameGSBNFPCKFDU !42

@lisa_shashkova AssertionError Variables !43 def vars_in_assert(e): tb = e.__traceback__ frame
= tb.tb_frame code = frame.f_code line = tb.tb_lineno - code.co_firstlineno + 1 source = inspect.getsource(code)

@lisa_shashkova AssertionError Variables !44 def get_vars_names(source, line): # get variables
names with `ast` module def vars_in_assert(e): tb = e.__traceback__ frame = tb.tb_frame code = frame.f_code line = tb.tb_lineno - code.co_firstlineno + 1 source = inspect.getsource(code) for name in get_vars_names(source, line): pass

@lisa_shashkova AssertionError Variables !45 def get_vars_names(source, line): # get variables
names with `ast` module def vars_in_assert(e): tb = e.__traceback__ frame = tb.tb_frame code = frame.f_code line = tb.tb_lineno - code.co_firstlineno + 1 source = inspect.getsource(code) for name in get_vars_names(source, line): if name in frame.f_locals: var = frame.f_locals[name] print(f"{name} = {var}")

@lisa_shashkova Usage !46 >>> try: assert a + b <
1 except AssertionError as e: vars_in_assert(e)

@lisa_shashkova Usage !47 >>> try: assert a + b <
1 except AssertionError as e: vars_in_assert(e) File “/file.py", line 10, in foo assert a + b < 1 Variables Values: a = 1 b = 2

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest !48

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest w %FCVHHFS !49

@lisa_shashkova Debugger !50

@lisa_shashkova Python Debugger w 5SBDJOHGVODUJPO w 'SBNFFWBMVBUJPOGVODUJPO !51

@lisa_shashkova Tracing Function w tracefunc(frame, event, arg) w sys.settrace(tracefunc) -
TFUUPDVSSFOUGSBNF w 4UPSFEJOBGSBNFframe.f_trace w %FCVHHFSBOBMZTFTFWFOUT !52

@lisa_shashkova Frame Evaluation w frame_eval(frame, exc) w %FCVHHFSJOTFSUTCSFBLQPJOU`TDPEFJOUPDPEFPCKFDU !53

@lisa_shashkova More About Debuggers w 1Z$PO64 w l%FCVHHJOHXJUI1ZUIPO#FUUFS 'BTUFS 4USPOHFSz
!54

@lisa_shashkova Access to Frame w tracefunc(frame, event, arg) w frame_eval(frame,
exc) !55

@lisa_shashkova Debugger: Location !56 w frame.f_code.co_filename BOE frame.f_lineno

@lisa_shashkova Debugger: Variables !57 w frame.f_locals

@lisa_shashkova Debugger: Frames !58 w frame.f_back

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest w %FCVHHFS !59

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest w %FCVHHFS w $PEFDPWFSBHF !60

@lisa_shashkova Code Coverage w 4IPXTXIJDIMJOFTXFSFFYFDVUFE !61

@lisa_shashkova coverage.py !62 w 5IFNPTUQPQVMBSDPEFDPWFSBHFMJCSBSZ

@lisa_shashkova coverage.py !63 • tracefunc(frame, event, arg) • frame.f_code.co_filename BOE
frame.f_lineno

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest w %FCVHHFS w $PEFDPWFSBHF !64

@lisa_shashkova Development Tools w "TTFSUJPO&SSPSJOpytest w %FCVHHFS w $PEFDPWFSBHF w
3VOUJNFUZQJOHUPPMT !65

@lisa_shashkova Typing Tools w 1Z"OOPUBUFCZ%SPQCPY w .POLFZ5ZQFCZ*OTUBHSBN w l$PMMFDU3VOUJNFJOGPSNBUJPOzJO  1Z$IBSN
!66

!67

!68

!69

!70

@lisa_shashkova Acces To Frame w 1Z"OOPUBUF .POLFZ5ZQF • sys.setprofile(profilefunc) •
profilefunc(frame, event, arg) !71

@lisa_shashkova Acces To Frame w l$PMMFDU3VOUJNFJOGPSNBUJPOzJO1Z$IBSN w *OUFHSBUFEXJUI%FCVHHFS w "DDFTTUPBGSBNFPCKFDU
!72

@lisa_shashkova Collecting Types !73 def arg_names(co): nargs = co.co_argcount names
= co.co_varnames return list(names[:nargs]) names = arg_names(frame.f_code)

@lisa_shashkova Collecting Types !74 def arg_names(co): nargs = co.co_argcount names
= co.co_varnames return list(names[:nargs]) names = arg_names(frame.f_code) locs = frame.f_locals objects = [locs[n] for n in names]

!75

3VOUJNFUZQJOHUPPMT w !76

@lisa_shashkova Concurrent Execution w 5ISFBET w "TZOD5BTLT !77

@lisa_shashkova Python Threads !78 import threading def fun(): print("Hello!") t
= threading.Thread(target=fun) t.start() t.join()

@lisa_shashkova Synchronisation w -PDLGVOEBNFOUBMTZODISPOJTBUJPOPCKFDU !79 lock = threading.Lock() lock.acquire() #
only one thread here lock.release() with lock: # equivalent

@lisa_shashkova Deadlock w 8BJUJOHGPSSFTPVSDFTXIJDIDBO`UCFSFMFBTFE !80

@lisa_shashkova Deadlock !81 def run1(): with lock1: with lock2: #
do sth def run2(): with lock2: with lock1: # do sth else Thread(target=run1).start() Thread(target=run2).start()

@lisa_shashkova Deadlock w 8BJUJOHGPSSFTPVSDFTXIJDIDBO`UCFSFMFBTFE w )BSEUPEFUFDUJOCJHQSPKFDUT !82

@lisa_shashkova Thread States •sys._getframe() - GSBNFPCKFDUGPSDVSSFOUUISFBE •sys._current_frames() - UPQNPTUTUBDLGSBNFGPSFBDIUISFBE !83

@lisa_shashkova Thread Handler w 1SJOUUSBDFCBDLTGPSUISFBETXJUIJOUFSWBM w )FMQUPpOEEFBEMPDLMPDBUJPO !84

@lisa_shashkova Fault Handler •faulthandler.dump_traceback(file) •%VNQTUIFUSBDFCBDLTPGBMMUISFBETJOGPpMF •*NQMFNFOUFEOBUJWFMZ !85

@lisa_shashkova Concurrent Execution w 5ISFBET w "TZOD5BTLT !86

@lisa_shashkova Async Locks !87 alock = asyncio.Lock() alock.acquire() # only
one task here alock.release() async with alock: # equivalent

@lisa_shashkova Async Fault Handler •asyncio.all_tasks(loop) - BMMUIFSVOOJOHUBTLT •Task.get_stack() - MJTUPGTUBDLGSBNFTGPSUIJT5BTL
!88

@lisa_shashkova Async Fault Handler w *OBTFQBSBUFUISFBE !89 def dump_traceback_later(timeout, loop):
while True: sleep(timeout) dump_traceback(loop, timeout)

@lisa_shashkova Async Fault Handler w *OBTFQBSBUFUISFBE !90 def dump_traceback(loop): for
task in asyncio.all_tasks(loop): task.print_stack() def dump_traceback_later(timeout, loop): while True: sleep(timeout) dump_traceback(loop, timeout)

3VOUJNFUZQJOHUPPMT w "TZOD 'BVMU)BOEMFS !91

@lisa_shashkova The Hidden Power of Runtime w 1ZUIPO3VOUJNFJTWFSZQPXFSGVM w &BTZBDDFTTUPTUBDLGSBNFBOEDPEFPCKFDUT
w %FWFMPQNFOU5PPMT w QZUFTU %FCVHHFS $PEF$PWFSBHF   5ZQJOH*OGPSNBUJPO 'BVMU  )BOEMFS !92

@lisa_shashkova Inspiration w 6TFFYJTUJOH3VOUJNF%FWFMPQNFOU5PPMT NPSFPGUFO w $SFBUFTPNFUIJOHOFX !93

@lisa_shashkova Links w IUUQTHJUIVCDPN&MJ[BWFUB1Z3VOUJNF5SJDLT w IUUQTEPDTQZUIPOPSH w FMJ[BWFUBTIBTILPWB!KFUCSBJOTDPN w !MJTB@TIBTILPWB
!94

The Hidden Power of the Python Runtime

The Hidden Power of the Python Runtime

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