pyliveupdate 0.3.1

A tool to manipulate python code at runtime for logging, profiling, debugging, etc.

PyLiveUpdate

PyLiveUpdate is tool to help you modify your running python code without stopping it. It is useful for modifying long-running server programs in production with zero downtime. Some modification scenario includes: inject code to profile the runtime of certain lines of code; inject code to print out a variable for debugging; apply a patch without restarting.

Install

pip install pyliveupdate

How to use

Put these two lines of code in your server program and run it

from pyliveupdatescripts import UpdateStub
UpdateStub().start()

Start a controller to modify it!

> pylu-controller -l 127.0.0.1:50050

Some predefined modification available in the controller

> FuncProfiler.profile('__main__.**') # inject the time profiling code into all functions in __main__
> LineProfiler.profile('__main__.bar', [11, 12]) # inject time profiling code into certain lines
> FuncDebugger.debug('__main__.bar') # inject code to print out function parameter and return value
> LineDebugger.debug('__main__.bar', [11, 12]) # inject code to print out variables in certain lines
> VarDebugger.debug('__main__.bar', 'b') # inject code to print out all values of a variable in different statements

You can also define your own customized modifications.

Customized modification

There are in general two kinds of modification: instrument and redefine:

Instrument code into existing functions

from pyliveupdate.update import Instrument, UpdateManager
def _line_after(a):
    print(a)
update = Instrument('__main__.bar', 
                    {('line_after', [12, 14]): _line_after})
UpdateManager.apply_update(update)

The code injects a print(a) in line 12 and 14 in function __main__.bar.

Redefine (patch) existing functions

from pyliveupdate.update import Instrument, UpdateManager
def new_bar(a):
    print('new_bar', a)
update = Redefine('__main__', None, {'__main__.bar':new_bar})
UpdateManager.apply_update(update)

The code redefines __main__.bar with new_bar.

Revert the modification

PyLiveUpdate also support to revert a modification on the fly:

> LU.ls() # list all modification
> LU.revert(1) # revert modifation with id 1