Restart debugging your program in the function that failed.
Project description
hot_restart
Restart debugging your program in the function that failed.
Installation:
pip install hot_restart
hot_restart
currently has no required dependencies outside the standard library.
If pydevd
is already imported, hot_restart
will use it to allow debugging
in VS Code (and other IDEs using pydevd
/ debugpy
).
Usage:
Wrap any function you expect to crash in @hot_restart.wrap
:
import hot_restart
@hot_restart.wrap
def my_func():
...
@hot_restart.wrap_class
class MyClass:
def forward(self, x):
super().forward(x * 2)
Alternatively, call hot_restart.wrap_module()
after your functions and
classes are defined.
When a wrapped function crashes, hot_restart will open a post mortem debugger in the wrapped function, with the rest of the stack still live above that function call.
Then you can modify the source code of your crashing function, and (c)ontinue from the debugger, and hot_restart will reload the source of that function (and only that function).
hot_restart
uses AST transformations to find new definitions, to avoid
causing "import-time" side effects, and to match line numbers with the real
source code while keeping each version of a function (except the initial load)
in its own source file.
Edge Cases
You can also trigger a full module reload with hot_restart.reload_module()
.
This may trigger "import-time" side effects and duplicate (i.e. conflicting)
class definitions. To avoid restarting your main function when reloading your
main module, check hot_restart.is_restarting_module()
.
hot_restart
uses source re-writing to handle the common cases, and does not
patch the byte-code of functions.
This limits hot_restart
from handling adding new variables to a closure or
adding methods to existing class instances, but simplifies the implementation.
super()
Calls
hot_restart rewrites super()
into super(type(self, self)
in reloaded source
(original source is loaded intact). This prevents methods from acquiring a
closure variable __class__
, which would break in many cases, but this
re-write can fail if self
is not defined where super()
is used. This
restriction may be removed in the future.
To work around this, you can use the two-argument form of super()
manually.
Closures and Nested Functions
hot_restart
will patch in old closure variables into newly defined functions,
as long as hot_restart.wrap
is the innermost decorator. However, functions
cannot add new closure variables without a full module reload. Functions can
still gain new arguments.
For nested functions, hot_restart.wrap_module()
cannot find the inner
function, so hot_restart.wrap()
must be used manually.
If hot_restart.wrap
is not the inner-most decorator, then closure variables
will be lost.
Alternative / Complementary Tools:
If you just want more complete hot reloading (for example, the ability to add
new methods to existing instances of classes), you should consider
jurigged. You should also be able to
use jurigged
with hot_restart
. If you want to use jurigged
's code
reloading with hot_restart
's function restarting, you can disable
hot_restart
's automatic code reloading by setting:
hot_restart.RELOAD_ON_CONTINUE = False
This module implements a workflow similar to "edit-and-continue". If you're looking for a more maximalist implementation of this workflow with IDE integration, you may be interested in Reloadium.
Although these useful alternatives exist, I created hot_restart
because
I found it difficult to debug failures in those systems.
hot_restart
intentionally implements a more minimal set of reloading routines
that I can easily wrap my head around.
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