如何将eval()函数与变量列表一起使用? [英] How to use eval() function with a list of variables?

问题描述

我有一个字符串函数列表:

I have a list of functions as strings:

["y + x + 3", "x**2 + y**2 - 17"]  # 2 functions in list

我有一个 Sympy Symbol 对象(基本上是变量)的列表，它们的 .name 属性与函数字符串中的变量名称相对应:

I have a list of Sympy Symbol objects (basically variables) whos .name attribute cooresponds to the variables names in the function strings:

[Symbol(x), Symbol(y)]
# list element 0's .name attribute is "x" 

我发现Python有一个名为 eval()的简洁函数，可以评估字符串，例如:

I found that Python have a neat function called eval() which can evaluate strings, for example:

x = 1
eval("x + 3") # Result should be 4

基本上，这就是我要对函数字符串进行的操作.但是，由于这是一个动态实现，因此我在程序中 eval()上方的一行中没有定义变量，因此它们位于列表中.例如，在上面的示例中x被定义为1，因此 eval()函数可以使用它.

Basically this is what I want to do with my functions strings. However, since this is a dynamic implementation I don't have variables defined on a line above eval() in my program, they are in a list instead. For example, in the example above x is defined as 1, so then the eval() function can use it.

但是我的变量在列表中，而不是在函数范围内定义为变量.如何使用 eval()函数并利用变量列表?

But I have my variables in a list, not defined as a variable in the scope of my function. How could I use the eval() function and utilize my list of variables?

推荐答案

eval 将局部变量作为第三个参数(

eval takes local variables as third argument(reference), so you can do this:

from sympy import Symbol
zs = [Symbol('x'), Symbol('y')]
eval('x+y', None, dict([z.name, z] for z in zs))

但是，也许您应该使用SymPy的一部分 parse_expr .

However, maybe you should use parse_expr which is part of SymPy.

from sympy import Symbol
from sympy.parsing.sympy_parser import parse_expr
zs = [Symbol('x'), Symbol('y')]
parse_expr('x+y', local_dict=dict([z.name, z] for z in zs))

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