What is the best way to implement Python macros for invoking reusable code in-situ?

General Discussions
1

What is the best way to implement Python macros for invoking reusable code in-situ?

I want to create a macro-like functionality in Python that can replace repetitive code wherever needed. Specifically, I would like to invoke the following code wherever I refer to MY_MACRO in my script:

# MY_MACRO
frameinfo = getframeinfo(currentframe())
msg = 'We are on file ' + frameinfo.filename + ' and line ' + str(frameinfo.lineno)
# Assumes access to namespace and the variables in which `MY_MACRO` is called. current_state = locals().items()

For example, here’s how I would like to use MY_MACRO in my code:

def some_function():
MY_MACRO
def some_other_function():
some_function()
MY_MACRO
class some_class:
def some_method(self):
MY_MACRO

I want to achieve the following:

  1. Avoid repeating the same code for MY_MACRO at different places in my script. A short and reusable construct is necessary.
  2. Ensure that the macro has access to the entire namespace of the scope in which it is called. This includes using locals().items() to access variables dynamically.
  3. Maintain correct behavior for frameinfo.lineno, so that the line number reported matches the actual line where MY_MACRO is used. Is there a way to implement macro-like functionality in Python, or a workaround that closely mimics this behavior? 5

What would be the easiest way to achieve this for Python macros?

2

You can achieve the functionality you’re looking for using Python macros with the MacroPy project. MacroPy brings syntactic macros to Python, which allows you to define reusable blocks of code that can be inserted anywhere in your code, just like macros in languages such as C.

While the project is still young (just 3 weeks old), it already has a collection of demos that show its potential. With MacroPy, you can implement the behavior you’re aiming for, including injecting code that has access to the current frame and the local variables.

3

Another way to achieve macro-like functionality in Python is by using its built-in introspection features along with exec.

You can dynamically generate and execute code at runtime, allowing you to simulate macros by embedding code directly into the current scope:

import inspect
def my_macro():
frameinfo = inspect.getframeinfo(inspect.currentframe())
msg = f'We are on file {frameinfo.filename} and line {frameinfo.lineno}'
current_state = locals().items()
print(msg, current_state)
def some_function():
exec("my_macro()")
some_function()

This approach uses exec to dynamically execute the my_macro code at the point where you want it, maintaining access to the local scope. It’s not as clean as using true macros, but it does allow for similar functionality.

4

If you’re willing to work within Python’s function and class structure, you can use decorators to inject your macro-like behavior into functions and methods.

While this won’t be as direct as using macros in other languages, it still allows for reusable code with access to the calling function’s namespace:

import inspect
def macro_decorator(func):
def wrapper(*args, **kwargs):
frameinfo = inspect.getframeinfo(inspect.currentframe().f_back)
msg = f'We are on file {frameinfo.filename} and line {frameinfo.lineno}'
current_state = locals().items()
print(msg, current_state)
return func(*args, **kwargs)
return wrapper
@macro_decorator
def some_function():
pass
some_function()

In this solution, the decorator macro_decorator simulates a macro by running the macro code before executing the decorated function. It allows for similar functionality, though it is still somewhat restricted by Python’s function-based model.