watchpoints 0.0.1

watchpoints monitors read and write on variables

watchpoints

watchpoints is an easy-to-use, intuitive variable/object monitor tool for python that behaves similar to watchpoints in gdb.

Install

pip install watchpoints

Usage

watch

Simply watch the variables you need to monitor!

from watchpoints import watch

a = 0
watch(a)
a = 1

will generate

<module> (my_script.py:5):
a:
0
->
1

It works on both variable change and object change

from watchpoints import watch

a = []
watch(a)
a.append(1)
a = {}

<module> (my_script.py:5):
a:
[]
->
[1]

<module> (my_script.py:6):
a:
[1]
->
{}

Even better, it can track the changes of the object after the changes of the variable

from watchpoints import watch

a = []
watch(a)
a = {}
a["a"] = 2

<module> (my_script.py:5):
a:
[]
->
{}

<module> (my_script).py:6):
a:
{}
->
{'a': 2}

Without doubts, it works whenever the object is changed, even if it's not in the same scope

from watchpoints import watch

def func(var):
    var["a"] = 1

a = {}
watch(a)
change(a)

func (my_script.py:4):
a:
{}
->
{'a': 1}

As you can imagine, you can monitor attributes of an object, or a specific element of a list or a dict

from watchpoints import watch

class MyObj:
    def __init__(self):
        self.a = 0

obj = MyObj()
d = {"a": 0}
watch(obj.a, d["a"])  # Yes you can do this
obj.a = 1
d["a"] = 1

<module> (my_script.py:10):
obj.a:
0
->
1

<module> (my_script.py:11):
d["a"]:
0
->
1

watchpoints will try to guess what you want to monitor, and monitor it as you expect(well most of the time)

unwatch

When you are done with the variable, you can unwatch it.

from watchpoints import watch, unwatch

a = 0
watch(a)
a = 1
unwatch(a)
a = 2  # nothing will happen

Or you can unwatch everything by passing no argument to it

unwatch()  # unwatch everything

monitoring variables will introduce a significant overhead, and should be used for debugging only.

alias

You can give an alias to a monitored variable, so you can unwatch it anywhere. And the alias will be printed instead of the variable name

from watchpoints import watch, unwatch

watch(a, alias="james")
# Many other stuff, scope changes
unwatch("james")

customize callback

Of course sometimes you want to print in your own format, or even do something more than print. You can use your own callback for monitored variables

watch(a, callback=my_callback)

The callback function takes three arguments

def my_callback(frame, elem, exec_info)

• frame is the current frame when a change is detected.
• elem is a WatchElement object that I'm to lazy to describe for now.
• exec_info is a tuple of (funcname, filename, lineno) of the line that changed the variable

You can also set change the callback function globally by

watch.config(callback=my_callback)

Use restore() to restore the default callback

watch.restore()

Bugs/Requests

Please send bug reports and feature requests through github issue tracker.

License

Copyright Tian Gao, 2020.

Distributed under the terms of the Apache 2.0 license.