python - Parsing an expression containing N using SymPy -

i parsing expression using sympy , getting following trace:

>>> parse_expr("3n", transformations=transformations)` typeerror: unsupported operand type(s) *: 'integer' , 'function' 

from gather, happens because n seen function parser , not other string. code works fine few other symbols tested.

can explain briefly why happening? there list of keywords or characters cannot parsed using parse_expr?

quoting docs (pitfalls , gotchas):

lastly, recommended not use i, e, s, n, c, o, or q variable or symbol names, used ... numeric evaluation (n() equivalent evalf() )... or better yet, use lowercase letters symbol names. python not prevent overriding default sympy names or functions, careful.