Pretty polynomial printing in python

Question

What format string would I use to print expressions like

2x^3 + 3x^2 - 6x + 1 (notice spaces on either side of signs)

30.1x^2 + 60.2x - 90.3

and (if straightforward)

x^2 + 2x + 1 (no coefficient on terms in x if coefficient is 1).

I've tried inserting padding between a forced sign like this:

"{0: =+}x^2 {1: =+}x {2: =+}".format(1, -2, 3)

but no padding appears.

What is source data structure for your expression? Is it string or function or list or what? — vittore, Dec 23 '13 at 18:56
I don't think this is an unreasonable question, but please demonstrate some effort by showing what you've got so far (and also explaining your data structures). — NPE, Dec 23 '13 at 18:59
Also, for kicks you could display things using `u"⁰¹²³⁴⁵⁶⁷⁸⁹"` — Eric, Dec 23 '13 at 20:39

score 3 · Answer 1 · answered Dec 23 '13 at 20:11

Since you didn't specify, I assume that your expressions are already in string form and you only need to make them look better. In that case, adding spaces on either side of signs can be done with a simple replace call.

def add_spaces_to_either_side_of_signs(s):
    return s.replace("+", " + ").replace("-", " - ")

expressions = [
    "2x^3+3x^2-6x+1",
    "30.1x^2+60.2x-90.3",
    "x^2+2x+1"
]

for expression in expressions:
    print "non-pretty version:", expression
    print "pretty version:    ", add_spaces_to_either_side_of_signs(expression)

Result:

non-pretty version: 2x^3+3x^2-6x+1
pretty version:     2x^3 + 3x^2 - 6x + 1
non-pretty version: 30.1x^2+60.2x-90.3
pretty version:     30.1x^2 + 60.2x - 90.3
non-pretty version: x^2+2x+1
pretty version:     x^2 + 2x + 1

Eric · Accepted Answer · 2013-12-23T20:50:30.123

Assuming you have [1, -6, 3, 2] representing "2x^3 + 3x^2 - 6x + 1":

class Polynomial(list): 
    def __repr__(self):
        # joiner[first, negative] = str
        joiner = {
            (True, True): '-',
            (True, False): '',
            (False, True): ' - ',
            (False, False): ' + '
        }

        result = []
        for power, coeff in reversed(list(enumerate(self))):
            j = joiner[not result, coeff < 0]
            coeff = abs(coeff)
            if coeff == 1 and power != 0:
                coeff = ''

            f = {0: '{}{}', 1: '{}{}x'}.get(power, '{}{}x^{}')

            result.append(f.format(j, coeff, power))

        return ''.join(result) or '0'

>>> Polynomial([1, -6, 3, 2])
2x^3 + 3x^2 - 6x + 1
>>> Polynomial([1, -6, 3, -2])
-2x^3 + 3x^2 - 6x + 1
>>> Polynomial([])
0

score 0 · Answer 3 · edited May 23 '17 at 11:44

If you really want your output to look great, like this is for a paper you want to publish or something, you can output LaTeX that typesets your equation.

http://oneau.wordpress.com/2011/12/25/latex-sympy/

Print latex-formula with python

Also, do you know about the Sage math tool? It combines Python with numerous math libraries. If you use Sage, you can work with symbolic equations and your "workbooks" will show the equations rendered by TeX. Sage uses a subset of TeX written in JavaScript to typeset your equations! Note: Sage made the choice to use the ^ operator for exponentiation, as you are doing in your example. In Sage you can type equations using ^ rather than **.

http://www.sagemath.org/doc/tutorial/tour_algebra.html

http://sagemath.org/

score 0 · Answer 4 · answered Dec 23 '13 at 20:25

0

import re

expressions = ["2x^3+3x^2-6x+1", "30.1x^2+60.2x-90.3", "x^2+2x+1"]

for i in expressions:
  print re.sub('.', lambda m: {'+':' + ', '-':' - '}.get(m.group(), m.group()), i)

answered Dec 23 '13 at 20:25

alvas

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Pretty polynomial printing in python

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