Thanks for such an amazingly fast and detailed reply!
On 15/04/2022 21:32, Aaron Meurer wrote:
Yes, you can have it separate. The location of a function in the code
has no bearing on its behavior.
That is good!
When you run 'import bailey' then 'bailey' will be the module (because
you called your file bailey.py). To get the function do
from bailey import bailey
I tried that too, but I got:
>>> bailey(a+3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\PythonSystem\lib\site-packages\sympy\core\cache.py", line
70, in wrapper
retval = cfunc(*args, **kwargs)
File "C:\PythonSystem\lib\site-packages\sympy\core\function.py", line
476, in __new__
result = super().__new__(cls, *args, **options)
File "C:\PythonSystem\lib\site-packages\sympy\core\cache.py", line
70, in wrapper
retval = cfunc(*args, **kwargs)
File "C:\PythonSystem\lib\site-packages\sympy\core\function.py", line
288, in __new__
evaluated = cls.eval(*args)
File "C:\SymPyProject\bailey.py", line 9, in eval
# Value at zero
TypeError: 'Add' object is not subscriptable
Alternatively I tried:
>>> (a+3).bailey(1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'Add' object has no attribute 'bailey'
You can't add new methods to existing SymPy objects. The first way you
tried is the correct way to access your bailey function.
I admit to being fairly confused at this level! What I would like to
know is:
1) Can I experiment in this way without actually adding files to
SymPy itself or modifying anything there already?
2) I would expect to get back a function call: bailey(a+3) or
perhaps the answer 1.
The function as you've written it will just return 1. If you want a
symbolic answer, eval() needs to return None (which is also the same
as not returning anything).
Since your eval() always returns something, the function will never be
symbolic. It is effectively no different from a normal Python function
def bailey(x):
if x == 0:
return 0
else:
return 1
To be absolutely clear, the actual content of the function is just junk
at this point - I am just trying to get the basic mechanism to work.
David
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