NoPdb: Non-interactive Python Debugger
- Installation:
pip install nopdb - Docs: https://nopdb.readthedocs.io/
NoPdb is a programmatic (non-interactive) debugger for Python. This means it gives you access to debugger-like superpowers directly from your code. With NoPdb, you can:
- capture function calls, including arguments, local variables, return values and stack traces
- set "breakpoints" that trigger user-defined actions when hit, namely:
- evaluate expressions to retrieve their values later
- execute arbitrary code, including modifying local variables
- enter an interactive debugger like pdb
NoPdb is also a convenient tool for inspecting machine learning model internals. For example, this notebook shows how to use it to visualize Transformer attention in PyTorch.
NoPdb should run at least under CPython and PyPy. Most features should work under any implementation as long as it has sys.settrace().
Note: This project is in its early development stage. Contributions and improvement ideas are welcome.
Capturing function calls
The functions capture_call() and capture_calls() allow capturing useful information about calls to a given function. They are typically used as context managers, e.g.:
with nopdb.capture_calls(fn) as calls:
some_code_that_calls_fn()
print(calls) # see details about how fn() was called
The information we can retrieve includes the function's arguments, return value, local variables and stack trace. For example:
>>> with nopdb.capture_call(f) as call:
... g(1)
>>> call
CallCapture(name='f', args=OrderedDict(x=1, y=1), return_value=4)
>>> call.print_stack()
File "<stdin>", line 2, in <module>
File "<stdin>", line 2, in g
File "<stdin>", line 1, in f
>>> call.args['x']
1
>>> call.return_value
4
>>> call.locals
{'y': 1, 'x': 1, 'z': 2}
Setting breakpoints
Like conventional debuggers, NoPdb can set breakpoints. However, because NoPdb is a non-interactive debugger, its breakpoints do not actually stop the execution of the program. Instead, they allow executing actions scheduled in advance, such as evaluating expressions.
To set a breakpoint, call the breakpoint() function. A breakpoint object is returned, allowing to schedule actions using its methods such as eval() and exec(). For example:
# Break at line 3 of the file or notebook cell where f is defined
with nopdb.breakpoint(function=f, line=3) as bp:
x = bp.eval("x") # Schedule an expression
type_y = bp.eval("type(y)") # Another one
bp.exec("print(y)") # Schedule a print statement
some_code_that_calls_f()
print(x, type_y) # Retrieve the captured values
There are other ways to specify the breakpoint location. For example:
# Break at any line with the given source code in the given file
with nopdb.breakpoint(file="pathlib.py", line="return obj") as bp:
...
# Break as soon as any function with the given name is called
with nopdb.breakpoint(function="myfunc") as bp:
...
Not only can we capture values, we can also modify them!
>>> with nopdb.breakpoint(function=f, line=3) as bp:
... # Get the value of x, then increment it, then get the new value
... x_before = bp.eval('x')
... bp.exec('x += 1')
... x_after = bp.eval('x')
...
... some_code_that_calls_f()
>>> x_before
[2]
>>> x_after
[3]
Planned features
Functionalities that do not exist, but could be added in the future:
Breakpoint.callback()for calling a given callback function, passing information about the current frame as an argument.Breakpoint.jump()for jumping to a different line in the same function.- A way to disable breakpoints.
Limitations
- Like Pdb, NoPdb only works with pure-Python functions. Calls to built-ins and C extensions cannot be captured. This also applies to ML frameworks that compile models into static graphs; for NoPdb to work, this feature needs to be disabled, e.g. with
tf.config.run_functions_eagerly(True)in TensorFlow and with thejax.disable_jit()context manager in JAX. - Local variable assignment in
Breakpoint.exec()is only supported under CPython and PyPy.
1.5k Jan 1, 2023
21 Nov 27, 2022
1.1k Dec 26, 2022
1 Nov 10, 2021
2 Jan 2, 2022
21 Jun 17, 2022
687 Nov 20, 2022
332 Dec 7, 2022
3.6k Jan 6, 2023
2.8k Jan 08, 2023
156 Jan 01, 2023
2.6k Jan 01, 2023
42 Dec 12, 2022
2.7k Jan 08, 2023
3.7k Jan 01, 2023
32.9k Dec 31, 2022
5 Feb 08, 2022
637 Jan 02, 2023
156 Dec 28, 2022
101 Aug 26, 2022
1 Nov 16, 2021
0 Feb 09, 2022
5.9k Dec 30, 2022
1 Dec 30, 2021
3k Jan 01, 2023
3k Jan 07, 2023