在sympy中运行表达式的AST

本文介绍了在sympy中运行表达式的AST的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在使用sympy计算复杂函数表达式的一些高阶导数。我想遍历表达式的AST，例如首先通过节点深度。我该怎么做？

I'm using sympy to compute some higher order derivatives of a complicated function expression. I'd like to traverse the AST of the expression, e.g. go through the nodes depth first. How do I do that ?

推荐答案

简单的深度优先旅行是这样的：

A simple depth-first travel would be like this:

from sympy import pi, sin from sympy.abc import a,x,y def depth_first_traverse(expr): for arg in expr.args: depth_first_traverse(arg, depth+1, new_marks+'+---', parent_ind=ind) if len(expr.args) == 0: # we reached a leaf of the tree pass # do something with leaf expr else: pass # do something with compound expr depth_first_traverse(sin(a*x*pi+1.5)/y)

带有附加参数，更多可以达到复杂的目标，例如以深度优先的顺序打印树，同时显示所有内容如何组合在一起：

With additional parameters, more complex goals can be reached, for example printing the tree in depth-first order while showing how everything fits together:

from sympy import srepr, pi, sin from sympy.abc import a,x,y def depth_first_traverse(expr, depth=0, marks='', parent_ind=None): for ind, arg in enumerate(expr.args): new_marks = marks.replace('+', '|').replace('-', ' ') if parent_ind == 0: new_marks = new_marks[:-4] + ' ' + new_marks[-3:] depth_first_traverse(arg, depth+1, new_marks+'+---', parent_ind=ind) if len(expr.args) == 0: print(marks, end="> ") print("symbol", srepr(expr)) else: print(marks, end="+ ") print("function", expr.func, "had", len(expr.args), "arguments") print(marks.replace('+', '|').replace('-', ' ')) depth_first_traverse(sin(a*x*pi+1.5)/y)

输出：

+---> symbol Symbol('y') | +---> symbol Integer(-1) | +---+ function <class 'sympy.core.power.Pow'> had 2 arguments | | +---> symbol Float('1.5', precision=53) | | | | +---> symbol pi | | | | | +---> symbol Symbol('a') | | | | | +---> symbol Symbol('x') | | | | +---+ function <class 'sympy.core.mul.Mul'> had 3 arguments | | | +---+ function <class 'sympy.core.add.Add'> had 2 arguments | | +---+ function sin had 1 arguments | + function <class 'sympy.core.mul.Mul'> had 2 arguments