内部结构发生变化时打印sympy的整个表达式对象

Question

So as the question says i want to print an entire expression object when internal structure of its tree changes, but as the sympy objects are immutable i cannot to do this with the name the object is bound to

Here is an example of Code on how i am changing the Internal Structure

from sympy import *
from sympy.abc import x,y

input = 'x*(x+4)+3*x'
expr = sympify(input,evaluate=False)

def traverse(expr):
    if(expr.is_Number):
        return 1,True
    oldexpr = expr
    args = expr.args
    sargs = []
    hit = False
    for arg in args:
        arg,arghit = traverse(arg)
        hit |= arghit
        sargs.append(arg)

    if(hit):
        expr = expr.func(*sargs)
        return expr,True
    else:
        return oldexpr,False

print(srepr(expr))
expr,hit = traverse(expr)
print(expr)

here i am changing the number to 1 whenever i encounter a number in the expression tree. And i want to print the complete expression when i made the change like this: x*(x+1)+3*x and then x*(x+1)+x Can anyone suggest me on how to achieve this.

Answer 1

Just a slight mod to what you have might be what you are looking for:

def traverse(expr):
  if any(a.is_Number and abs(a) != 1 for a in expr.args):
    print(expr,'->',expr.func(*[(a if not a.is_Number else 1) for a in expr.args]))
  if expr.is_Number and abs(expr) != 1:
    return 1, True
  oldexpr = expr
  args = expr.args
  sargs = []
  hit = False
  for arg in args:
    arg,arghit = traverse(arg)
    hit |= arghit
    sargs.append(arg)

  if(hit):
    expr = expr.func(*sargs)
    return expr, True
  else:
    return oldexpr, False

This produces

>>> traverse(2*x+3)
(2*x + 3, '->', 2*x + 1)
(2*x, '->', x)

(x + 1, True)

/c