sympy: Symbols and their expressions

symbols_expr.py

# using a symbol and associated expression in sympy
from sympy import *
init_printing()

i, L = symbols('i, L')
s_beta = symbols('beta')
e_beta = i * pi / L

Eq(s_beta, e_beta)

sympy_symbol_expression_problem.markdown

Sympy: symbols vs expressions

Consider this: β=iπ/L

If we want to model this in sympy, we need both the symbol β and the expression iπ/L.

If we also declare beta as a symbol, beta=symbols('beta'), we get a nice symbol, that prints as β. But when if we try to assign the expression to it, beta = i * pi * L, a disconnect between variable beta and the symbol beta (β) happens. Python variable beta is now overwritten with the expression, and doesn't point to symbol β anymore.

Solution: Define both symbol and the associated expression in a consistant manner.

s_beta = symbols('beta')    # symbol beta
e_beta = i * pi / L         # expression beta

This will give us power to use the symbol and the expression in any calculation.

Run the code in sympy live.