parse_expr bug with splitting symbols and undefined function

[Duane Nykamp]

The following throws an error

In [27]: f=Function('f')

In [28]: parse_expr('af(t)', local_dict={'f': f }, transformations=(auto_symbol, auto_number, split_symbols, implicit_multiplication))
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

[snip]

TypeError: unbound method as_base_exp() must be called with f instance as first argument (got nothing instead)


The code it is trying to evaluate is

Symbol ('a' )*(f )*(Symbol ('t' ))

It seems the problem is the parentheses around f that were inserted in line 394:
                            result.extend([(OP, '('), (NAME, "%s" % char), (OP, ')'),
                                           (NAME, 'Symbol'), (OP, '(')])

Is there any reason to add those parenthesis?  Certainly, if char is a function, they should not be added.  I'm not sure if there are cases where one does need those parenthesis.

I can fix the problem by changing this line to
                                result.extend([(NAME, "%s" % char),
                                           (NAME, 'Symbol'), (OP, '(')])
but I'm not sure if I should test if local_dict[char] or global_dict[char] is callable (similar to _get_token_callable) and only remove the parenthesis if it is callable.

For this to work, I also have to modify the approach to remove the last 2 tokens (rather than 3) and then skip the following token so that the close parenthesis from the original Symbol is not included.

Does this fix seem reasonable?

Duane

[Aaron Meurer]

Go ahead and open a pull request with this change, and we can review
it, and see if it breaks any tests, and so on.

Aaron Meurer

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[Duane Nykamp]

OK. I added a pull request: https://github.com/sympy/sympy/pull/8307