如何修改sympy的打印顺序? [英] How to modify sympy's printing order?

问题描述

我正在使用 sympy 编写代数表达式并使用它们执行基本计算.Sympy 没有跟踪变量的顺序，这在打印表达式时可能是一个问题(这个问题已经被提出 此处 和此处，所以这不是重复的).例如

<预><代码>>>>从 sympy 导入 *>>>var("p,a")>>>l=p-1-a；>>>打印(l)；-a+p-1

然而，sympy 似乎按字母顺序打印变量.有没有办法改变 Python 所指的字母顺序，从而诱使 sympy 以所需的顺序打印变量?欢迎任何其他解决方案！

解决方案

感谢 smichr 的回答，我写了一个自定义打印机，它可以满足我的需求.我不是一个好的程序员，所以如果你对我的代码有任何建议，我很乐意实现它们.

from sympy import *导入数学导入副本进口藏品导入迭代工具init_printing(use_unicode=True)var("p,a,b,c,d,e,f");ddict=collections.OrderedDict([(p, 1),(a, 2), (b, 3), (c, 4),(d, 5),(e, 6),(f, 7),])from sympy import Basic, Function, Symbol从 sympy.printing.printer 导入打印机从 sympy.printing.latex 导入 print_latex从 sympy.core.basic 导入基本类 MyPrinter(打印机):打印方法 = '_myprinter'def _print_Add(self,expr):expr_args=expr.argsdef new_place(el):如果 el 在 ddict 中:返回 ddict[el]别的:返回 len(ddict)+1def get_place(el):如果 el.is_integer:返回 new_place(el)elif el.is_symbol:返回 new_place(el)elif len(el.args)>0:如果 el.args[len(el.args)-1].is_symbol:返回 new_place(el.args[len(el.args)-1])别的:返回 0别的:返回 0def write_coeff(el):如果 el.is_integer:如果el＞0:返回 "+%s" %el别的:返回 "%s" %elelif el.is_symbol:返回 "+%s" %elelif len(el.args)>0:如果 el.args[len(el.args)-1].is_symbol:如果 el.args[0].is_rational:如果 el.args[0]>0:返回 "+%s" %latex(el)别的:返回 "%s" %latex(el)别的:返回 "%s" %latex(el)别的:返回 "%s" %latex(el)别的:返回 "%s" %ellist_place=[get_place(a) for a in expr.args]expr_args=zip(*sorted(zip(list_place,expr_args)))[1]to_print=[write_coeff(a) for a in expr_args]to_print[0]=str(latex(expr_args[0]))return "".join(a for a in to_print)def my_printer(expr):返回 (MyPrinter().doprint(expr))de=-a+p+3+c-b打印(my_printer(de))

I am using sympy to write algebraic expressions and perform basic calculations with them. Sympy does not keep track of the order of the variables which can be a problem when it comes to printing expressions (the issue has already been raised here and here, so this is not a duplicate). e.g.

>>> from sympy import *
>>> var("p,a")
>>> l=p-1-a;
>>> print(l);
-a+p-1

However, sympy seems to print the variables in the alphabetical order. Is there a way to change the alphebetical order Python refers to and thus trick sympy into printing the variables in the desired order? Any other solution is welcome!

解决方案

Thanks to smichr's answer, I wrote a custom printer which does what I want. I am not a good programmer, so if you have any suggestions to make on my code, I would be happy to implement them.

from sympy import *
import math
import copy
import collections
import itertools
init_printing(use_unicode=True)
var("p,a,b,c,d,e,f");
ddict=collections.OrderedDict([(p, 1),(a, 2), (b, 3), (c, 4),(d, 5),(e, 6),(f, 7),])
from sympy import Basic, Function, Symbol
from sympy.printing.printer import Printer
from sympy.printing.latex import print_latex
from sympy.core.basic import Basic
class MyPrinter(Printer):
    printmethod = '_myprinter'
    def _print_Add(self,expr):
        expr_args=expr.args
        def new_place(el):
            if el in ddict:
                return ddict[el]
            else:
                return len(ddict)+1
        def get_place(el):
            if el.is_integer:
                return new_place(el)
            elif el.is_symbol:
                return new_place(el)
            elif len(el.args)>0:
                if el.args[len(el.args)-1].is_symbol:
                    return new_place(el.args[len(el.args)-1])
                else:
                    return 0
            else:
                return 0
        def write_coeff(el):
            if el.is_integer:
                if el>0:
                    return "+%s" %el
                else:
                    return "%s" %el
            elif el.is_symbol:
                return "+%s" %el
            elif len(el.args)>0:
                if el.args[len(el.args)-1].is_symbol:
                    if el.args[0].is_rational:
                        if el.args[0]>0:
                            return "+%s" %latex(el)
                        else:
                            return "%s" %latex(el)
                    else:
                        return "%s" %latex(el)
                else:
                    return "%s" %latex(el)
            else:
                return "%s" %el
        list_place=[get_place(a) for a in expr.args]
        expr_args=zip(*sorted(zip(list_place,expr_args)))[1]
        to_print=[write_coeff(a) for a in expr_args]
        to_print[0]=str(latex(expr_args[0]))
        return "".join(a for a in to_print)
def my_printer(expr):
    return (MyPrinter().doprint(expr))
de=-a+p+3+c-b
print(my_printer(de))

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