Polynomial functions in python

Question

I am very new in writing Python code. I have to represent polynomial like this,

4x^230+7x^96+1

testP = [[4,512],[7,256],[1,0]]

def printPoly2(P):
    for i in range(len(P)):
        if P[i] != 0:
            print("%s x^%s + "%(P[i], i)),
            print

printPoly2(testP)

but my answer is not correct. I need help on this.

I'm not making the connection between your opening example polynomial, and your representation of it as a list of lists. Should testP not be: [[4,230],[7,96],[1,0]] ? — Thomas Kimber, Feb 02 '16 at 17:02
I guess it should. But P in your method is a list of lists. So P[i] returns a list and you compare it to != 0 which makes no sense. — Rainer, Feb 02 '16 at 17:05
Unpacking the list of lists as follows should yield the results I think the OP is looking for 2 changes, first the *if* clause could be: if len(P[i]) != 0 And secondly, the following print statement as print("%s x^%s + "%(P[i][0], P[i][1])), — Thomas Kimber, Feb 02 '16 at 17:08
Sorry, testP should be like this, testP = [[4,512],[7,256],[1,0]] — tani, Feb 02 '16 at 17:14

xgord · Answer 1 · 2016-02-02T17:25:12.447

Your problem is in the print statement. By writing:

print("%s x^%s + "%(P[i], i))

You are actually printing the entire tuple. For example, P[0] equals the entire list [4, 512]. So in directly printing P[i] you're just printing the entire sublist.

Instead, you want to print each element in the sublist.

print("%s x^%s" % (P[i][0], P[i][1]))

Additionally, your solution as-is will print each part of the answer on a separate line. To fix this you have a couple options, but here's one that doesn't depend on the python version you have. Basically, you create a string that represents your result, and keep building on it as you go through the loop. Then at the very end of the function, you print that string.

result = '' # initialize an empty string before your loop

Then inside your loop replace the print call with:

result = "%s + %s x^%s" % (result, P[i][0], P[i][1]

And at the very end of the function you can print the string.

print (result)

score 0 · Answer 2 · answered Feb 02 '16 at 17:13

0

I (hopefully) improved your code with some pythonic magic. Now it´s a list of tuples and uses automatic tuple-unwrapping.

testP = [(4, 230), (7, 96), (1, 0)]

def printPoly2(P):
    for i, e in P:
        if e != 0:
            print("{} x^{} + ".format(i, e))

printPoly2(testP)

Prints out

4 x^230 + 
7 x^96 +

answered Feb 02 '16 at 17:13

Rainer

761
5
20

1

You still need to print the constant term without `x^0`. – chepner Feb 02 '16 at 17:15
@chepner I think so too, but that was the original post^^ tani, you maybe should add an else case and just print out the "i" – Rainer Feb 02 '16 at 17:39

Rainer · Answer 3 · 2016-02-03T08:13:25.233

0

Just had 5 more minutes... here you go

testP = [(4, 230), (7, 96), (1, 0)]

def printPoly2(polynom):
    parts = []
    for i, e in polynom:
        parts.append(_format_polynome(i,e))

    print " + ".join(parts)

def _format_polynome(i, e):
    if e == 0:
        return "{}".format(i)
    else:
        return "{} x^{}".format(i, e)

printPoly2(testP)

edited Feb 03 '16 at 08:13

answered Feb 02 '16 at 17:46

Rainer

761
5
20

Lynch · Answer 4 · 2016-02-03T04:44:47.913

this is how I would write this code in something I think is a more pythonic way of writting it:

def poly2(P):
    result = []
    for item in P:
        n, e = item
        if e == 0:
            result.append("1")
        else:
            result.append("{}x^{}".format(n, e))
    return " + ".join(result)

# 4x^230 + 7x^96 + 1
testP = [(4,230), (7,96), (1,0)]
print poly2(testP)

note that its more flexible to return a string representation than to print it directly from the function.

Polynomial functions in python

4 Answers4